9 the Land Resources of North East Nigeria A/Blume1 the Environment

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The Land Resources of North East Nigeria Volume 1 The Environment

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Photo: P E Glover Nomadic bulls grazing arable stubble. Savanna woodland in the background

11 Foreign and Commonwealth Office Overseas Development Administration

The Land Resources of North East Nigeria

Volume 1 The Environment (with an introduction to Volumes 1 - 5 by the Editor, P. Tuley)

P.J. Aitchison, M.G. Bawden, D.M. Carroll P.E. Glover, K. Klinkenberg, P.N. de Leeuw and P. Tuley

Land Resource Study No. 9

Land Resources Division, Tolworth Tower Surbiton, Surrey, England

1972 THE LAND RESOURCES DIVISION

The Land Resources Division of the Overseas Development Administration, Foreign and Commonwealth Office, assists developing countries in mapping, investigating and assessing land resources, and makes recommendations on the use of these resources for the development of agriculture, livestock husbandry and forestry; it also gives advice on related subjects to over seas governments and organisations, makes scientific personnel available for appointment abroad and provides lectures and training courses in the basic techniques of resource appraisal.

The Division works in close co-operation with government departments, research institutes, universities and international organisations concerned with land resources assessment and development planning.

The Division ceased to be a part of the Directorate of Overseas Surveys in April 1971.

iv CONTENTS

LIST OP PLATES vi

LIST OP TEXT MAPS vi

LIST OP DETACHED MAPS vii

LIST OP FIGURES vii

INTRODUCTION TO VOLUMES 1-5

LIST OP VOLUMES xi

PREFACE BY THE EDITOR History of the Study xiii Abstract xiii Resume xiii Method xiv Bibliographic Studies xiv Acknowledgements xiv List of Contributors to Volumes 1-5 XV

VOLUME 1 PART 1. INTRODUCTION

Acknowledgement s 3

Abstract 3

Resume 3 List of Descriptors 3

PART 2. THE ENVIRONMENT PHYSICAL ASPECTS

Location M G Bawden 5 Climate P Tuley 6

Physiography M G Bawden 43 Geology M G Bawden 46 Geomorphology M G Bawden 60 Hydrology M G Bawden 71

Soils D M Carroll and K Klinkenberg 85 Vegetation P N de Leeuw and P Tuley 121 Fauna P J Aitchison and P E Glover 156 HUMAN ASPECTS

History P Tuley 163 Population P Tuley 164 Communications P Tuley 166

PART 3. REFERENCES 175 LIST OF PLATES

Frontispiece. Nomadic bulls grazing on arable stubbles

1/1. Song. View from basalt hill across farmland with Adansonia digitata and Acacia albida 54 1/2. Biu Plateau. General view northward from Tilla Lake with cones and craters in the far distance 54

1/3. The Kadi Escarpment 55

1/4. Near Pindinga. Exposure of the Pindinga Shale in river bank in

predominently Gombe Sandstone 55

1/5. The road to Dikwa across the 'firki' (black cracking clay plains) 69

1/6. The Bama Ridge just west of Maiduguri 69

1/7. The Gongola Floodplain 70

1/8. The Matyoro Lakes 70

1/9. Near Gulumba. Termitaria on heavy soils in Land System Vil, the Yabiri Delta 120 1/10. Soil erosion at the western foot of the Biu Plateau resulting from intensive utilisation of Ferruginous Tropical Soils derived from rocks of the Basement Complex 1^ 1/11. Typical Anogeissus Woodland south of Damboa 127

1/12. Lannea humilis. A typical gregarious clump showing the low contorted habit 127

1/13. Acacia seyal Tree Savanna on vertic clay flat 141

1/14. Land System Vel, the Arege Plain. Cordia rothii/Acacia raddiana Tree and

Shrub Savanna with thickets of Salvadora persica 141

1/15. Hyphaene Palm Bush on the Yobe Floodplain 155

1/16. Riparian Woodland on the course of the river Yedseram, north of the Bama Ridge 155 LIST OF TEXT MAPS

1. Location 7

2. Major relief units 9

3. Mean annual rainfall 11

4a, 4b. Mean monthly rainfall 18,19

5a, 5b. Mean monthly temperature 26,27

6a,6b. Mean monthly maximum temperature 30, 31

7a, 7b. Monthly analysis of wind direction 33,35

8. Length, start and end of the wet season 41

9. Geology 47

vi ÏO- Hydrogeology 73

11- Catchment areas 75

HA. Areas covered t>y reconnaissance soil surveys 84 12- Population density 167 13- Ethnic groups 169 14- Administrative units 171

15- Communications 173

LIST OF DETACHED MAPS 1. Relief 2- Geomorphology 3- Soils 4- Vegetation

LIST OF FIGURES 1. Distribution of rainfall for selected stations 21 2. Rainfall dispersion diagrams for selected stations 23 3- Mean daily hours of bright sunshine and cloud cover 37 4. Mean saturation deficit at 0900 and at 1500 hours 38 5- Eco-climatic zones 39 6. Geological sect ions 52,53 "7. Generalised soil patterns 86 8. Soil patterns on Basement Complex 97 9. Soil patterns on Cretaceous Sandstones 100 10. Soil patterns on Transitional Formations 103 11. Clay content of three soils on Kerri Kerri Sandstone 105 12- Soil patterns on toasa.lt 108 13- Soil patterns on sanely facies of Chad Formation 114 14. Soil patterns in alluvial areas 115 15. Environment al relat ionships of the major woody plant communities 124 16- Alluvial complexes — woody vegetation. Schematic relationship of the 125 major plant «communit ies

vil INTRODUCTION TO VOLUMES 1- 5 LIST OF VOLUMES LAND RESOURCE STUDY NO. 9. THE LAND RESOURCES OF NORTH EAST NIGERIA. EDITED BY P TULEY

Volume 1 The Environment (with an Introduction to Volumes 1-5) (1972) Volume 2 Tsetse and Trypanosomiasis (1970) Volume 3 The Land Systems (1972) Volume 4 Present and Potential Land Use (1972) Volume 5 Appendixes and Tables (1972)

xi PREFACE TO VOLUMES 1 - 5

by the Editor, P. Tuley

HISTORY OF THE STUDY This study is published with the authority of the Nigerian Federal and North-Eastern State Governments. The data collected and collated, and the recommendations evolved during the course of the investigations associated with this study, formed the basis for discussion at a Land Resources Conference organised by the North-Eastern State Government in August 1969 (Land Resources Conference, Maiduguri, 1970). The final approved recommendations presented in this study are essentially those discussed and submitted to the Nigerian authorities at that meeting.

Political changes in Nigeria have resulted in the creation of 12 states. The area covered by this study (Text Map 1), the boundaries of which were negotiated by the former Northern Nigeria Government and predate the present structure, falls entirely within the present North-Eastern State. The intention was to investigate an area of Nigeria north of the Benue river and east of 10° longitude. As explained in the Location Section, Volume 1, the boundary has been adjusted slightly in the light of subsequent developments.

The origins of the study lie in two United Kingdom Technical Assistance Projects requested by the former Northern Nigeria Government. The first request was for an investigation commenc ing in 1965 by a team under the leadership of Dr P E Glover on the feasibility of eradicating tsetse from a substantial area in the northeast of Nigeria. Details of the project are given in Volume 2 and draft reports have been submitted to the Nigerian authorities (Glover and Aitchison, 1967; Lesslie, 1968). The second request was for an investigation of the land resources of the area to be carried out by the Land Resources Division. Work on this project commenced in 1966 and an interim report was subsequently submitted to the Nigerian authorities (Bawden etal., 1968).

During the period of these projects the Soil Survey Section, Institute for Agricultural Research, Ahmadu Bello University, Samaru, Zaria, agreed to a programme expanding its exist ing soil survey coverage in the area. Details of this programme are contained in the Soils Section of Volume 1.

With this programme of synchronised and interrelated projects it quickly became apparent that unnecessary duplication could easily occur. In consequence, it was agreed by all concerned that the Land Resources Division should prepare and publish a consolidated study.

ABSTRACT This study (Volumes 1-5) comprises the quantified reconnaissance assessment of the land resources of 176 000 km2 (68 000 mi2) in North East Nigeria. The fundamental environmental factors are described. A full volume is devoted to the problems and eradication of the tsetse fly while another classifies the area into 123 land systems with descriptions provided at the land facet level. The present land use of the area is described and recommendations are made for future land use.

(An abstract of Volume 1 will be found in Volume 1, Part 1.)

RESUME

Cette etude (Tomes 1/5) comprend une reconnaissance quantifiee des ressources terrestres de 176 000 km2 du nord-est du Nigeria. Les elements fondamentaux du milieu sont decrits. Un volume complet est consacre' aux problèmes et ä 1'extirpation de la mouche Tse'tse, tandis qu'un autre classe la re'gion dans 123 land systems (zones e'cologiques), avec des descriptions detaillees des unites constitutives de chaque zone ecologique. L'usage actuel de la terre dans la zone est de'crit, et des recommendations sont faites pour son usage ä 1'avenir.

Un re'sume de Tome 1 se trouve dans la première Partie de ce tome-ci. xiii METHOD This study has attempted to apply the Land System concept, broadly in the sense of Christian and Stewart (1964), to the environmental classification of a substantial area, 176 000 km2 (68 000 mi2). Description of the main parameters at the land facet level for 123 land systems has also been attempted and the whole employed as a framework within which land use data and recommendations are classified and presented. The study has been largely agroforestal in emphasis but it is hoped it will prove useful in such other fields as engineering and industrial planning.

The data and recommendations are presented in terms of "natural units' , but since State planning procedures are largely based on administrative units, a set of administrative over lays for the larger scale maps has been provided for the North-Eastern State authorities.

Attention should be drawn to the efforts in Volume 4 and in the appendices in Volume 5, to provide areal estimates of land facets and the vegetation/land use patterns upon them. Subsequently, quantified data, fundamental to land use and development planning, can be derived from the estimates.

BIBLIOGRAPHIC STUDIES Prom the large quantity of bibliographic material accumulated during the project only references strictly relevant to each volume have been retained. It is however being arranged for a subject land resource bibliography to be issued in conjunction with this study (Posnett et al., 1972).

ACKNOWLEDGEMENTS To thank everyone associated with this study would be a monumental task as there must be few relevant organisations and arms of government in Nigeria that have not assisted willingly and generously in the implementation of the various projects. To complicate matters further, following administrative changes, some of the organisations deeply involved at the inception of the projects no longer exist. Special mention must however be made of the efforts and support, often in times of difficulty and even national emergency, of :

The Ministry of Animal and Forestry Resources and Ministry of Agriculture of the former Northern Nigerian Government (whose work with regard to this project later devolved upon the North-Eastern State Ministry of Natural Resources); the Federal Tsetse Control Unit, including elements of the former Ministry of Health's Sleep ing Sickness Service; and the Interim Common Services Agency.

The Institute for Agricultural Research, Ahmadu Bello University, Samaru, primarily through the agency of the Soil Survey Section and the Shika Research Station.

The British High Commission and Trade Commission, Kaduna.

A study of this nature must use the accumulated knowledge of organisations and individuals conversant with the project area. Every attempt has been made to acknowledge sources of data and individuals in the text of the report and the assistance of all concerned is most gratefully acknowledged. The organisations primarily concerned are :

Federal Ministry of Agriculture and Natural Resources North-Eastern State, Ministry of Natural Resources North-Eastern State, Ministry of Works North-Eastern State, Ministry of Health Federal Surveyor General Surveyor General, ICSA (Interim Common Services Agency) Surveyor General, North-Eastern State Nigerian Geological Survey Federal Tsetse Control Unit Nigerian Institute for Trypanosomiasis Research Institute for Agricultural Research, Ahmadu Bello University, Samaru Savanna Forestry Research Station, Samaru Nigerian Meteorological Services

xiv United States Agency for International Development UNESCO/PAO Chad Basin Commission Commonwealth Development Corporation

Outside Nigeria the assistance of the following contributed greatly to the study :

ORSTOM (Office de Recherche Scientifique et Technique Outre-Mer, Prance) M M Bocquier and M M Gavaud

The Department of Geography, Liverpool University, United Kingdom Mr R A Pullan

The Atlas Computer Laboratory, Chilton, United Kingdom Mr J E Hailstone and Mrs J Lay

The Royal Botanic Gardens, Kew, United Kingdom Mr P N Hepper and Dr W D Clayton

In conclusion, thanks must-go to all local administrators, officials and citizens whose courtesy, kindness and willingness to assist contributed so much to the effectiveness of the field work.

LIST OF CONTRIBUTORS TO VOLUMES 1-5 P J AITCHISON Started his tropical service in Swaziland and has been actively engaged in tsetse survey and control in Kenya and Nigeria for 13 years prior to joining the present project. Now farming in the United Kingdom.

M G BAWDEN Joined the Forestry and Land Use Section of the Directorate of Overseas Surveys (the forerunner of the Land Resources Division) in 1959 as geomorphologist. Has worked primarily in West and Southern Africa.

D M CARROLL A member of the United Kingdom Overseas Pool of Soil Scientists from 1962 until its absorption by the Land Resources Division in 1965. Worked mainly on soil survey in the West Indies, Southern and West Africa. In 1968 joined the Soil Survey of England and Wales.

P E GLOVER Formerly Chief Zoologist to the Kenya Veterinary Department. In 1965 appointed as a Land Use Adviser to the United Kingdom Ministry of Overseas Development to take charge of the tsetse investigations described in this study. Presently working on the Tsavo National Park Project in Kenya.

K KLINKENBERG Joined the Soil Survey Section of the Institute for Agricultural Research, Samaru, in 1957. Has been largely concerned with Soil Survey in the Northeast of Nigeria and has been Head of the Section since 1967.

P N de LEEUW Joined the Ministry of Agriculture, Northern Nigeria, in 1960 as ecologist/ soil surveyor. In 1963 became a research fellow of the Institute for Agricultural Research primarily concerned with rangeland problems at the Shika Research Station, where he is now Officer-in-Charge.

A LESSLIE Formerly with the Ghana and Kenya Departments of Agriculture, from 1946 until retiring as Director of Agriculture, Eastern Region, Kenya, in 1964. Joined the Land Resources Division in 1967 on completion of the United Kingdom Technical Assistance project associated with this study.

P TULEY Formerly Regional Botanist then Head of the Agricultural Research and Train ing Station, Umudike, Nigeria. Joined the Land Resources Division in 1965 and now Project Leader for operations in the north of Nigeria. Acted as coordinating editor for this report.

xv r

VOLUME 1 PARTS 1- 3 PART 1. INTRODUCTION

ACKNOWLEDGEMENTS Sources of data are quoted in the text and full acknowledgements are given in the Introduction to Volumes 1-5 at the beginning of this study.

ABSTRACT The volume is devoted to the description of the physical and human environment of the project area. Present land use is however omitted and is described in Volume 4. An account is given of the geology, geomorphology, hydrology and climate. The soils and soil patterns are des cribed and the system of soil classification employed is explained. The vegetation of the area is classified into 20 phytosociological units, and the species composition of each displayed in tabular form. In addition to text maps there are maps of Relief, Geomorphology, Soils and Vegetation at a scale of 1:1 000 000.

RESUME On decrit le milieu physique et humain de la zone du projet. On ne discute pas 1'utilisation actuelle de la terre, qui sera decrite dans le Volume 4. Un recit est donne de la geologie, la geomorphologie, 1'hydrologie et du climat. Les sols et leurs groupements sont de'crits et le Systeme de classer les sols est explique. La ve'getation de la zone est classee dans 20 unites phytosociologiques, et la composition par espèces de chacune est presentee en forme de tableau. Le relief, la ge'omorphologie, les sols et la ve'ge'tation sont indiques sur des cartes ä 1*echelle de 1:1 000 000.

DESCRIPTORS FOR COORDINATE INDEXING Climate, geology, geomorphology, soil survey, cartography, hydrology, land resource, fauna, plant ecology, vegetation survey, communications, demography, North, East, Nigeria.

3 PART 2. THE ENVIRONMENT

LOCATION by M G Bawden

The area covered by this land resource project is shown in Text Map 1. It is bounded in the south by the Benue river and in the east and north by the frontier with the Cameroon and Niger Republics. The western boundary is generalised on the small scale location map as a straight line following 10° longitude; in detail it is more complex: from Matsena in the north through Hadejia to Azare it follows the 10° line of longitude; from Azare it runs east to Misau and then southwards separating the Bauchi Plains from the Kerri Kerri Plateau (see Text Map 2). Prom the south of the Kerri Kerri Plateau the boundary follows an irregular line southeast to the Benue, downstream from the confluence with the river Pai.

The reason for the irregular boundary is that, at the time of the fieldwork, a further land resource reconnaissance was known to be planned to cover the area immediately to the west of this project. To the north of Misau a similar landscape extends westwards from Gashua to Kano and 10° longitude was used as a convenient dividing line. South of Misau the landscape changes markedly between the Kerri Kerri Plateau and the Bauchi Plains to the west and the boundary follows this natural division. South of the Kerri Kerri Plateau the character of the Benue Valley west of the Pai river is more akin to the landscape further west and it will be covered by the new project.

In the south the North East project joins the area covered by the reconnaissance of the land resources of Southern Sardauna and Southern Adamawa (Bawden and Tuley, 1966) the northern limit of which was the Benue river extending eastwards from the 10° line of longitude to the Cameroon frontier.

5 CLIMATE by P Tuley

GENERAL CIRCULATION

The gross characteristics of the West African climate are largely determined by the properties and movement of the so-called Inter-Tropical Convergence Zone (ITCZ). The north ward progression of the sun during the summer season in the northern hemisphere brings rain- bearing southwesterly winds to the project area. Water for plant growth becomes available under conditions of increasing day length, and there is a close correlation between rainfall pattern and latitude. Conversely, with the southward movement of the sun in winter, northerly and northeasterly dry winds blow from the Sahara. Accounts of this phenomenon of relevance to the project area are available in Clackson (1957), Cochemé and Franquin (1967) and Hamilton and Archbold (1945). In the project area there is a marked southerly displacement, particularly in the extreme northeast of some of the climatic parameters. Cochemé and Franquin (1967) suggest that this is probably due to a 'preferred position' of a high pres sure cell lying to the northwest of Chad.

The southern sector of the project area also exhibits climatic anomalies due to orographic effects, while the low-lying Benue Valley appears to have a separate climatic regime for at least part of the year.

AVAILABILITY OF RECORDS

The prime source of data for this report has been the Monthly Summary issued by the Nigerian Meteorological Service (NMS). There is a reasonable distribution of stations within the project area recording rainfall, but there are key areas for which data are not available, are incomplete or are of short duration. In addition, there is a small group of stations, usually associated with airfields, where a wider range of measurements are taken: Maiduguri, Yola, Potiskum and Nguru. Limited data have been collected from reports giving records not shown in the Summaries and these sources are acknowledged in the text. There are also a few stations falling just outside the area, in Nigeria and adjacent countries, which provide use ful records. In Volume 5 a map showing the location of the recording stations is given, the sources of publications are listed and suggestions made for the siting of new stations in the project area.

To improve presentation, tables of selected data have also been placed in Volume 5 and only summarised data are given here. In association with other projects in Nigeria it is intended to present a separate and more detailed analysis of the available data at a later date.

PRECIPITATION Mean Annual Rainfall (1949-1961) The highest recorded mean annual rainfall (m.a.r.) in the project area is from Bazza, in the foothills of the Mandara range, with 1 125 mm (44.3 in) and the lowest from Abadan, in the extreme northeast of the area, with 290 m (11.5 in). The mean annual isohyets are shown in Text Map 3. To the north of the 890 m (35 in) isohyet the typical latitudinal trend is as expected, allowing for the dipping of the isohyets to the eastward described under General Circulation, and for some local southward displacement in the east behind the Biu Plateau and the northern tip of the Mandara range. To the south of this line a more complex situation arises. The 1 015 mm (40 in) isohyet enters the project area from the west just north of ll°ti. Near Misau it makes a sharp bend turning back on itself and progressing southwestward to the area of the confluence of the Wase and Donga rivers with the Benue. Here it turns again sharply eastward and, just south of the Benue, it follows a more typical east-west alignment passing into the Cameroon Republic just south of the Benue-Paro confluence (Genieux, 1960). In effect there is a spectacular broadening of the belt between the 6 LOCATION MAP 8° 16° 12°

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IAR Soil Surveys within Project Area

Roads Railways I I I I I I I I I I ^CALABA'R International Boundaries +- + - + —+- + N'kongsamba Kumbai State Boundaries ^. Scale 1:5.000.000 Miles 50 0 50 100 I L_J I I 1_ io|2y l I -r-l f DOUALA 50 100 150 4° I s»; East of Greenwich D.O.S.(L.R.)3072 Drawn and photographed by Directorate of Overseas Surveys, 1969. Copyright reserved Printed by Ordnance Survey. MAJOR RELIEF UNITS TEXT MAP 2 12*

SCALE 1:3,000,000 25 50 75

MANGA PLAINS ' OMatsena ^ *^ / CHAD; (LACUSTRINE

—^ -7^ GUDUMBALI y PLAINS DUNEFIELD Mon*°nu

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12° — ^^. ^v J^T^o^ COMPLEX r7 ~~l^_^ DAMATURU PLAINS^—^ ^'J -^ / / Potiikum \- " ~~~Z^"^ «^- BAMA DELTAIC f Damaturu POTISKUM , COMPLEX ) PLAIN \ /—?_ J ,* GONGOLA f yALLEY

BAUCHI /I NafadaO r \ LAJN^^ \ / BIU ^PLATEAU UBA KERRI KERRI PLAINS .?/ / PLATEAU / W'NDARA / I^JUNTAINS

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MAJOR RELIEF UNITS

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Escarpment

Bama Ridge _^_^_ Main Road

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+ + + + + +++ International Boundary

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9 MEAN ANNUAL RAINFALL TEXT MAP 3 10' 14"

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10° 12° East of Greenwich 14° D.O.S.(L.R.)3064G Based on data provided by the Nigerian Meteorological Service. Drawn and photographed by Directorate of Overseas Surveys, 1969. Copyright reserved Printed by Ordnance Survey, 1 015 mm (40 in) and 890 mm (35 in) isohyets, roughly enclosed in a rectangle bounded by 10°- 13° longitude and 9°- ll° N. Within this rectangle lies a distinct isolated belt of 1 015 mm (40 in) m.a.r. about 30-50 km (20-30 mi) wide running from the Hawal - Gongola con fluence to the Mandara range. In addition, smaller areas with a m.a.r. above 1 015 mm (40 in) and below 890 (35 in) also occur within the rectangle, associated with localised orographic effects. Where the presence of large atypical areas is suspected, but not fully substantiated, they are indicated by broken blue lines in Text Map 1. This feature is dis cussed further under eco-climatic zones.

Mean Monthly Rainfall The extent and distribution of mean monthly rainfall is shown on Maps 4a and 4b. The monthly means range from 450 mm (18 in) to zero. The period November - February is virtually rainless over the greater part of the project area and the rains commence in March -April sweeping up from the southwest and west to reach their peak in August. From September onwards the rains retreat southwestwards and the annual northwest/southwest oscillation is clearly observable on the maps. (See pp. 18-42 for climatic maps and diagrams.)

Distribution of Rainfall Figure 1 shows the distribution of the occurrence of annual rainfall for a restricted number of stations by (25 mm) 1 in integers and grouped 5 in (125 mm) units. Over the period examined it can be seen that low annual rains are atypical of the stations with a m.a.r. of more than 1 015 mm (40 in). Yola occupies an intermediate position with a wider scatter of records about the mean. In the northern group low rains occurred at Maiduguri in 6 years out of 40 and at Potiskum in 2 years out of 26. The lowest record occurred in the same year of drought, 1940, for both stations. The deviation from normal distributions indicated by the grouped histograms in Figure 1 should be noted and Figure 2 shows a range of typical rainfall patterns for selected stations.

Twin-Peak Distributions The annual distribution of rainfall in twin peaks is well known in southern Nigeria and involves what is commonly termed the 'little dry season' in the month of August between twin peaks of rainfall in July and September (Ireland, 1962). This is associated with the double passage northward and southward of the ICTZ at the time when it usually reaches its most northerly position. There are indications that the feature occurs in the south and south west of the project area, where the secondary minimum is July and not August (Kwojeffa is a marked exception). It appears to be confined to the rectangle between the 890- 1 015 mm (35-40 in) isohyets described under Mean Annual Rainfall, where, irrespective of total rain fall, there is a tendency for the predominance of August rainfall to be diminished with an additional tendency towards twin-peak distributions.

TEMPERATURE

Temperature records are available in the NMS Monthly Summary for four stations within our area, Maiduguri, Potiskum, Yola and Nguru. Fortunately there are some peripheral stations also recording temperature and Klinkenberg et al. (1963) give some figures for Gombe. From the restricted data available the broad trends of the temperature regime are shown on Text Maps 5a, 5b, 6a and 6b. Temperatures tend to be higher to the northeast and lower towards the southwest, with the marked exception of the Benue Valley which, particularly in the period December - March, experiences a higher temperature than the country immediately to the north. Excepting this, the area in general experiences the coolest temperatures in December - January, with monthly means falling to 20.0-22.5°C (68.0° - 72. 5°F). Night tem peratures of the order of 8°C(46°F) are recorded during this period and, at high altitude, lower temperatures may be experienced. In the Benue Valley,minimum temperatures rarely fall below 13°C (55°F). Temperatures reach their maximum at the onset of the rains in April -May. In April itself mean maximum temperatures over most of the area are in excess of 39°C (102°F) while mean temperatures are of the order of 31°C (88°F). Maximum day temperatures of around 43°C (110°F) are not uncommon in the north and northeast. During the rains an intermediate regime with "lower and more uniform temperatures occurs. Throughout the area temperatures above the norm for the time of year are experienced in low-lying areas and enclosed valleys.

13 WIND Strong winds often associated with squalls and storms do occur (Dorrell, 1947) but destruc tive winds are not common. Direction and persistence of the wind (Text Maps 7a and 7b) are however of paramount importance. It can be seen that, with the southerly movement of the ITCZ from October to April the wind blows consistently from the north or, more often, the northeast. During this period the area is exposed to very dry winds blowing from the Sahara, the harmattan, often carrying a thick haze of wind-borne, conspicuously diamataceous, dust (Bigelstone, 1958; McKeown. 1958). Prom May, throughout the summer rains until September, the direction is reversed and the wind blows mainly across the area from the southwest. Again the Benue Valley is somewhat exceptional. The dry season wind tends to blow more directly from the north while the wet season wind is more westerly and even north westerly orientated and commences earlier in March and finishes later in October, than the main part of the area.

Once this wind pattern is appreciated, the rationale of the rainfall/temperature pattern falls into place. Local anticyclonic effects modify the generalised southwest direction of wet season wind . in West Africa particularly in the south of the project area. The generalised wind movements explain the near-diagonal oscillation of rain and temperature in the northern sector. In the southern sector, the more westerly/northwesterly wind creates a pattern in the wet season of up-wind exposure and down-wind rain shadow effects, fluctuating around the critical 900-1 000 mm (35 - 40 in) isohyets. The high temperatures in the dry season in the Benue Valley are probably due to low altitude and the effects of the land to the north blocking the northerly orientated wind.

RADIATION Available data of relevance to the project area in the form of 'hours of bright sunlight' observations are restricted to Maiduguri, Bauchi, Ibi, Yola and Potiskum. Cochemé and Franquin (1967) also give useful data for the surrounding territories.

Figure 3 shows the monthly variation in incoming radiation. The general picture is of radia tion rising to a maximum in November - February and falling to a minimum in August. An interesting feature is the marked fall and recovery of the graph in the period February - April. In the far north this occurs in March and is probably associated with overcast con ditions due to the meeting of the 'dust front' with the ITCZ (Hamilton and Archbold, 1945). In the southern stations it is a month later and probably associated with increased rain cloud and storm conditions as the ITCZ retreats southward. It should be noted that Maiduguri, which occupies an intermediate position, merely shows a flattening of the graph during this period.

Included in Figure 3 are graphs for mean cloud cover which show a clear inverse relationship with the incoming radiation.

HUMIDITY Humidity follows a simple relationship with the change of the seasons. Figure 4 shows the monthly change in saturation deficit reaching a peak in the pre-rains hot period in March - April and falling to a minimum in August in the mid-rainy season. It also follows a simple inverse daily relationship with temperature reaching minimum values at night and maximum ones at the height of the day.

WATER BUDGET Unlike areas in the south of the country, radiation is not likely to be a limiting factor in plant growth and it is the availability of water that is of prime agricultural importance throughout the project area. Two approaches to the problem are possible; to consider the balance between precipitation gain and various forms of water loss largely calculated from climatic parameters, or to consider a level of precipitation based on past experience after which the 'rainy season' can be said to have 'safely' started or to have finished.

14 Potential Evapotranspiration

Discussion of the reason for using this parameter (PE) and the methodology employed in its calculation is beyond the scope of this report. Contributions of relevance to the survey area can be found in Cochemé and Pranquin (1967), Gamier (1960) and Ojo (1969). Despite cautionary canment from such authors as Sibbons (1962) and Stanhill (1965), calculations based on the method of Penman (1956) have been employed in deriving the generalised trends of PE shown in Figure 5.

As stated, radiation data are sparse in the project area, as are also adequate measurements for the aerodynamic factor of the Penman equation. Cochemé and Franquin (1967) were able to employ some transformations of aviation wind measurements and Bawden and Tuley (1966) produced a set of figures for Yola using a conversion of Beaufort Scale recordings. Neither of these methods appears fully satisfactory, particularly as there is evidence (Hudson, 1965) that the importance of the aerodynamic factor is greatly increased under conditions similar to those found during winter in a large part of the project area. The calculated PE for the project area follows an expected pattern, rising to a maximum in March - April and falling to a minimum in August - September. Figure 5 shows how the graph flattens under more northerly, drier, conditions.

Effective Rainfall The concept of 'effective rainfall' attempts to estimate the amount of rainfall available for plant growth, namely:

Precipitation - (Evaporation + Runoff + Deep percolation).

As shown in Figure 5, by combining PE and rainfall recordings a series of agriculturally use ful parameters can be derived for those situations where run-off and deep percolation do not assume serious proportions.

1. Humid Period: Rainfall > Evaporation 2. Intermediate Period: Rainfall > 0.5 x Evaporation 3. Moist period: 1+2

Once these periods are defined in terms of duration, with starting and terminating dates, what is commonly termed the 'growing season' or 'rainy season' can also be defined, the terms being largely synonymous with 'moist period' (Cochemé and Franquin, 1967).

The Wet Season Walter (1967) employs a more pragmatic approach in deriving this useful parameter. From his experience in West Africa he stipulates that the wet season in any calendar year is defined as falling between:

1. the date after 50 mm (2 in) of accumulated rainfall has fallen; 2. the date after which no more than 50 mm (2 in) remains to fall.

His classification for the area in these terms, for the project area, is shown on Text Map 8. It is interesting to note the close relationship between his calculations and those of Cochemé and Franquin (1967) based on the calculation of PE.

ECO -CLIMATIC TERMINOLOGY

Following the above review of the major climatic parameters, the validity of the generalised climatic terms commonly used in West Africa and applicable to the project area requires examination. Three major zones and one intermediate zone are involved (cf Koppen, 1931): 1. the Sahel Zone (approximating to a Koppen BSh climate); 2. The Sudan Zone (intermediate between a Koppen BSh-Aw climate); 3. The Sub-Sudan Zone; 4. The Northern Guinea Zone (approximating to a Koppen Aw climate)

15 Use of these terms has fallen into some disrepute, generally due to the looseness with which they have been applied (see comments under 'Vegetation') and to the view that they had proved so useful as a "blanket term' that investigations of the fundamental parameters involved had long been ignored. As originally conceived (Chevalier, 1900; Keay, 1953), the zones were established on the basis of an interrelated interpretation of rainfall records and vegetation/ land use observations. In the project area the Sahel, Sudan and Guinea Zones correspond res pectively with the m.a.r. areas shown on Text Map 3: < 508 mm (20 in), 508-1 016 mm (20- 40 in), and > 1 016 (40 in). Figure 5 attempts to characterise the zones in terms of some of the major parameters involved. It can be seen that the characteristics of the zones are so dominated by the rainfall pattern that a classification based on this alone has con siderable validity. The terms as defined in Figure 5 will therefore be used as climatic des criptions throughout the report.

The Sub-Sudan Zone This term (Clayton, 1957) has been the cause of much discussion. It occupies an approximate rectangle bounded on the west by the Mandara range, on the east by 10° longitude, by the Benue Valley on the south and by the 890 mm (35 in) isohyet on the north- In this area the marked displacement of the 1 015 mm (40 in) isohyet is attributable to the westerly and northwesterly orientation of the rain-carrying winds resulting in a large rain shadow behind the Jos highlands and giving rise to an atypical broadening of the inter-isohyet belt between 1 015 m and 890 mm (40 and 35 in). The major significance lies in the fact that the rainfall change between these isohyets is highly sensitive in its effect on other environ mental factors, a tension belt' in the sense of Fairbairn (1945). There is therefore an extremely marked orographic reaction to the westerly winds; open areas tend to be truly transitional, westerly faces tend to Northern Guinea conditions and easterly faces towards Sudan conditions. A good example is the belt of 1 015 mm (40 in) rainfall between the Biu Plateau and the sandstone hills to the south where the wind is forced upwards by the Mandara and Zummo Mountains. This effect dies out on the watershed, which forms the frontier with the Cameroon Republic.

MEAN MONTHLY RAINFALL TEXT MAl

Omm Oin

l-25mm (O-l-lin)

25-50mm (l-2in)

50-IO0mm (2-4in)

I00-I50mm (4-6in)

l50-200mm (6-8in) = = = 200-250mtn (8-1Oin)

250-30Omm (I0-I2in)

300-350mm (I2-I4in)

350-400mm (I4-I6in)

400-450mm (l6-1Sin)

D.O.S.(L.R.)3064H Based on data provided by the Nigerian Meteorological Ï Drawn and photographed by Directorate of Overseas Survey Copyright reserved Printed by Ordnance Ï MEAN MONTHLY RAINFALL TEXT MAP 4b

Omm Oin

l-25mm (0 1-lin)

25-50mm (l-2in)

50-100mm (2-4in)

100-ISOmm (4-6in)

l50-200mm (6-8in)

200-250mm (8-IOin)

250-300mm (I0-I2in)

300-350mm (I2-I4in)

350-400mm (I4-I6in)

400-450mm (l6-18in)

D.O.S.(L.R.)3064J. Based on data provided by the Nigerian Meteorological Service. Copyright reserved Drawn and photographed by Directorate of Overseas Surveys, 1969. Printed by Ordnance Survey, Distribution of rainfall for selected stations Figure I

BAUCHI 1947-1964 Mean annual rainfall 1100mm (43 in)

IIJ II I I ! I I I I I I I II I ! I I 1M I I I I mill»» i i 10 15 20 25 30 35 40 45 50 53in 5 H—i—i—10 15 20 25r 3-i0 35 40 L45 50 55i n BIU 1940-1962 (Missing data for 3 years) Mean annual rainfall 1000mm (40 in) 15-

I I I I I I I I I I I I I I I I I I ! I I 1I I I I I I MUIIWI I I I U -|—i—i—r iJL YOLA 1916-1963 (Missing data for 6 years) Mean annual rainfall 965mm (38 in) P 5-1 15-

O 2-

• 11111111111 I Hüll I mi POTISKUM 1936-1963 (Missing data for I year) Mean annual rainfall 810mm (30 in)

i i i11 ii1 i1 1P ii Ii i1 1i i i irr i lAJiWlir 11 in m n i n i ln Jrnl i i i 11 i M i i 1—r MAIDUGURI 1915-1963 (Missing data for 8 years) Mean annual rainfall 660mm (26 in)

10 15 20 25 30 35' 40 45 50 53in 5 10 15 20 25 30 35 40 45 50 55 in 500 750 1000 1250 mm Annual rainfall

D.O.S. 3099 A

21 Rainfall dispersion diagrams - selected stations Figure 2

Group'I < 500mm (20 in) mm ABADAN GEIDAM YUSUFARI MONGONU * r 500 290mm (I IS in) 310mm (125in) 430mm (17 in) 455mm (18 in) 480mm (19 in) 4 yrs 5 yrs 10 yrs 15 yrs 7 yrs

- 125

" TTTT~r~r—-^"r™""""T I ViT »'MI' I' » VOVD' I f n J n I ) » s o M o |lftlH||tS0N0 | I N I 11 | | » S 0 K D |IH»n||IS0H0 Group 2 500-900mm (20-35 in) POTISKUM BASH AR* r 500 810mm 890mm (35 in) 5 yrs

Group 3 900-l000mm (35-40 in) DUMBOA KWOJEFFA KALTUNGO' BIU 940mm fl 965mm (38 in) 965mm (38 in) 1000mm (40 in) (37 in) 9 yrs 5 yrs 22 yrs 9 yrs 375

Group 4 > 1000mm (40 in) DARAZO * SHANI* MUBI BAUCHI BAZZA * 1000mm (40 in) 1040mm (41 in) 1040mm (41 in) 1070mm 1120mm (44 in) (43 in 6 yrs 7 yrs II yrs 6 yrs 12 yrs 375

IH1HJ|»SI)N0 | t H I H | | » S 0 K D |FB»H||»S0N0 |i n » H | | F fi » n | | i s 0 N D

^ Highest recorded maximum B Mean O Lowest recorded minimum Distribution of mean monthly rainfall only

DOS. 3099 B 23

MEAN MONTHLY TEMPERATURE ("**+"•") TEXT M,

20 l°-22-5°C (68 l°-72-5°F)

22-6°-250°C (72-6°-770°F)

25l°-27-5°C (77 l°-8l 5°F)

27 6°-30 0°C (81 6°-860°F)

30 l°-32 5°C (86 l°-90-5°F)

D.O.S.(L.R.)3064K Based on data provided by the Nigerian Meteorological Drawn and photographed by Directorate of Overseas Survc Copyright reserved Printed by Ordnance MEAN MONTHLY TEMPERATURE (MAX+"IN) TEXT MAP 5b

D.O.S.(L.R.)3064L Based on data provided by the Nigerian Meteorological Service. Copyright reserved Drawn and photographed by Directorate of Overseas Surveys, 1969. Printed by Ordnance Survey, MEAN MONTHLY MAXIMUM TEMPERATURE TEXT MAP 6a

D.O.S.(L.R.)3064M Based on data provided by the Nigerian Meteorological Service. Copyright reserved Drawn and photographed by Directorate of Overseas Surveys, 1969. Printed by Ordnance Survey. MEAN MONTHLY MAXIMUM TEMPERATURE TEXT MAP 6b

25I°-27S°C (77 l°-8l-5°F)

27 6°-300°C (8l-6°-86 0°F)

30l°-32-5°C (86 l°-90-5°F)

32-6°-350°C (90-6°-950°F)

35l°-37-5°C (95I°-99 5°F)

376°-400°C (99-6°-l04 0°F)

40l°-42-5°C (I04I°-I08 5°F)

D.O.S.(L.R.)3064N Based on data provided by the Nigerian Meteorological Service. Copyright reserved Drawn and photographed by Directorate of Overseas Surveys, 1969. Printed by Ordnance Survey. MONTHLY ANALYSIS OF WIND DIRECTION TEXT MAP 7a

,/|\ APRIL

The figures represent the number of occasions on which the wind direction was recorded, observations being taken thrice daily.

D.O.S.(L.R.)3064O Based on data provided by the Nigerian Meteorological Service. Copyright reserved Drawn and photographed by Directorate of Overseas Surveys, 1969. Printed by Ordnance Survey. MONTHLY ANALYSIS OF WIND DIRECTION TEXT MAP 7b

D.O.S.(L.R.)3064P Based on data provided by the Nigerian Meteorological Service. Copyright reserved Drawn and photographed by Directorate of Overseas Surveys, 1969. Printed by Ordnance Survey. Mean daily hours of bright sunshine and mean daily cloud cover in Oktas Figure 3

Oktas „»,.,.... Hours ,„, Oktas BAUCHI 10 IBI

- 9

«—*\ ' ^x ' x-^f \ >—x< / - 7 \_ - S \

- 6 - ^

- 5 - 0

Approx annual total-3000 hrs Approx annual total-2750 hrs

-| 1 1 1 1 1 1 1 1 1 1 1— 1 1 1 1 1 1 1 1 1 1 1 r— JFMAMJJASOND JFMAMJ JASOND

YOLA 10 -, MAIDUGURI ,.

- 9 -

8 - X 7 - - 5

\ ' x. \ \_ - 6 - N,

0- S - - 0

Approx annual total-3000 hrs Approx annual total-3200 hrs

"i—i—i—i—i—i—i—i—i—i—r "i—i—i—i—i—i—i—i—i—i—i—r

MAINE SOROA 10 - NGUIGMI % A

9 - V 8 -

7 - - 5 V 6 -

5 -

Approx annual total-3150 hrs Approx annual total-3300 hrs 4 "I 1 1 1 1 1 1 1 1 1 1 r- ~ i i i i i i i i i i r J FMAMJ JASOND J FMAMJ JASOND * Based on limited data - see Volume S Cloud x x x Sunshine •---•--•

D.O.S. 3099 C

37 Mean saturation deficit (mb) at 0900 and at 1500 hours G.M.T. Figure 4 Millibars 60-1 BAUCHI

50-

40- 1500 hours

30-

0900 hours

20-

10-

~l 1 1 1 \ 1 1 1 1 1 1 1 JFMAMJJASOND Months Millibars 60 YOLA

50-

1500 hours 40-

30-

0900 hours

20-

10-

~l 1 I 1 I 1 1 1 1 1 1 1 J FMAMJJASOND Months Millibars 60 MAIDUGURI

50-

40- 1500 hours

30-

20 0900 hours

10-

"1 I 1 I I I I I 1 1 1 1 J FMAM J JASOND Months

D.O.S. 3099 D 38 Eco-climatic zones in the project area Formalised modal climatic parameters Figure 5 mm in 300 12 -l Moist Period * Humid Period* ' 1 1 - NORTHERN /^ GUINEA / \ 250 10- Annual rainfall > 1000mm ( 40in ) 9 - **« / \ * Length of rainy season 150-170 days. C °F * / \ End of April-Mid October 200 8 • T-40 * * / \ 100 * * / \ Annual potential evapotranspiration 7 - * * / \ * * / \ I600-I800mm (63-71 in) * % / \ Toul annual hours of bright sunlight 2700-3000 150 6 - *>+"' ° ° ° h V 5 - /".," o o-V o / •••+•••- \

100 4 -

3 -

50 2 -

o o M A M |

300 12 Moist Period* I I SUDAN

250 10 Annual rainfall 500-1000mm (20-40in) 9 * Length of rainy season 90-150 days. May-September 200 8 *- -* Annual potential evapotranspiration 7 I800-2000mm (71-80 in)

150 6 Total annual hours of bright sunlight 3000-3300

70 100 4 --20

3 60

50 2 --10 50

M A M J A S O N D

SAHEL

250 10 Moist Period* Annual rainfall < 500mm (20 in) 9 • Length of rainy season 60-90 days. 200 8 June- Mid September Annual potential evapotranspiration 7 I800-2000mm (71-80 in)

150 6 Total annual hours of bright sunlight 3000-3300

80 5

100 4 20 7°

3 60

50 2 --10 50

M j | + + + + + Potential evapotranspiration " sensu Walter (1967) Rainfall o o Temperature ' sensu Cocheme and Franquin (1967)

D.O.S. 3099 E

39 LENGTH, START & END OF THE WET SEASON TEXT MAP 8 10° 12° 14° 14° i i

SCALE 1:3,000,000

MILES 0 25 50 75 100 MILES

1st JULY T + + + + + + +- + + *•+ + + + + + + + +• S---.+ - - ,« OMacsena ., *"^. *N» * **X^V_Ü V _.••

N^W^ Giffhua (|,.!V>. ^T.,J,„>

^^w>^y^S^p ~ / Mongonu • / Hadejia „

V/ / \«r. • * blkwa°J^ / . 140 Y 12° • 12° ^^ / *3JJ*^ MAIDUGURlX ^* \ 14*0 Potiskumt Damaturun»»-k^ K ^^N^^" ^^ •** "**.^s •^Iv^ ^vJ """ ~tH20

O Damboa '120

'140

— #- 10th OCT

_Hawa\,

"iGombe j y / .1». , V 10° f / ••*' >£ 10° /..••• •. X ^T s j Song — ^ .> 'S* tltungc >o" 4 f /K 160 ,.•• / • ••' / 1st MAY

180

20th OCT

1st MAY Date of start of the wet season

'60 Length of wet season in days

——-— Main Road _ _ __ 20th OCT Date of end of the wet season '200 H 1 1- Railway

*+++++++ International Boundary

10° 12° East of Greenwich 14° D.O.S.(L.R.)3064R Based on Walter (1967). Drawn and photographed by Directorate of Overseas Surveys, 1969. Copyright reserved Printed by Ordnance Survey, PHYSIOGRAPHY by M G Bawden

The range of relief in the North East project area is shown on Map 1. This altitude information has been obtained from various sources. The Directorate of Overseas Surveys has published 1:50 000 scale maps (DOS series 430) with a contour interval of 15.24 m (50 ft) of the area east of Numan and south of Buni and Bama. West of Numan similar maps are being prepared by the Directorate and here, altitude data have been derived mainly from spot heights and road and rail survey traverses. These data have been related to the land system classification of the landscape, which is partly based on an interpretation of the relief from aerial photography. Parts of the area north of a line roughly from Bama west to Azare have been contoured during hydrological investigations; there is little variation in gross relief in this area.

There has been no comprehensive account of the physiography of the area covered by the North East project since Falconer (1911) described the geology and geography of northern Nigeria. Grove (1957) described the main physiographic regions in Nigeria within the Benue catchment and Klinkenberg et al. (1963) have described the physiographic units within the Gongola Valley. Grove (1958), Grove and Pullan (1963) and Grove and Warren (1968) have described the major landforms in Nigeria within the Chad Basin and Pullan (1964) has described the landforms southwest of Lake Chad in more detail. Brief descriptions of other areas within the North East project area are contained in various Soil Survey Bulletins from the Institute for Agricultural Research, Samaru.

The major relief units which occur in the North East project area are shown on Text Map 2. Because of the interrelation between the relief, the landform and the underlying rocks, most of the major relief units coincide with the land regions defined in Volume 3. Some major relief units contain more than one land region where the landforms within the major relief unit are formed on contrasting rock types, or are the product of more than one geomorphological process, or are the product of more than one cycle of erosion, or where one unit is sensibly contained by another at the smaller scale of the major relief unit map.

The project area can be considered in two parts, north and south, separated by the boundary between Quaternary rocks of the Chad Formation and the older formations which lie to the south (see Text Map 9). Apart from the Basement plains which lie north of Mubi, and the Mandara Mountains on the extreme eastern border of the area, this twofold geological division roughly coincides with the divide between the northeasterly flowing rivers which drain to Lake Chad and the south and southwesterly flowing tributaries of the Benue (see Text Map 11).

The northern part of the survey area consists almost entirely of extensive flat or very gently undulating plains descending gradually from 450 m (1 500 ft) in the south and west to 275 m (900 ft) on the shores of Lake Chad. The very gentle relief of these plains, the vertical difference between the highest and lowest levels seldom exceeding 15 m (50 ft), con tinues as far south as Mubi in the upper reaches of the Yedseram river and is only broken along the frontier with the Cameroon Republic where the Mandara Mountains rise to over 1 000 m (3 300 ft). The southern part is more varied. The centre of the area is dominated by the Gongola Valley which descends from 450 m (1 500 ft) to 150 m (500 ft) at the con fluence with the Benue. The Valley is bounded on the west by the high ground of the Kerri Kerri Plateau and on the east by the Biu Plateau and the Gaanda Hills. Northwest of these Hills the gentle relief of the Uba Plains extends eastwards to the Mandara Mountains where the highest peaks reach over 1 200 m (4 000 ft).

The Manga Plains, which lie in the northwest of the area, are composed of alluvial and aeolian sands overlying the Basement Complex and Younger Granite pediment to the hill range further north in the Niger Republic. The southern limit of these plains is marked by the Yobe River Complex which extends from Kano (west from the survey area) to Lake Chad in the northeast. This river complex comprises extensive ancient river courses, deltas and alluvial plains, many of which have been resorted by wind action and are now largely drift-covered. It also contains flooded remnants of longitudinal dunes of the Lantewa Dunefield as well as the present floodplain of the Yobe river and its tributaries. South of the Yobe River Complex a further series of aeolian sand plains extend southwards to the Benue watershed. These plains also contain largely drift-filled relics of a more extensive drainage system.

43 The west and central portions of these plains contain extensive northeast-orientated longi tudinal dunes are are part of the 'Ancient Erg of Hausaland' (Grove, 1958). The Lantewa Dunefield merges southwards into the Damaturu Plains which are a series of sand plains with very little relief. The cover of aeolian sand is thinner south of Damaturu and, along the southern border of these plains, clays and sandstones of the Chad Formation are exposed beneath the drift. Between Buni and Damboa the plains are underlain by rocks of the Basement Complex and by Cretaceous sediments. Between Potiskum and Azare aeolian drift sands similar to those of the Damaturu Plains overlie sandstones of the Kerri Kerri Formation and form the extensive Potiskum Plain. Apart from occasional flat-topped ironstone-capped hills this plain has very little variation in relief.

In the northeast the longitudinal dunes of the Lantewa Dunefield are replaced by transverse northwest-orientated dunes of the Gudumbali Dunefield. These dunes rise as much as 15 m (50 ft) above the interdune areas. North of Mongonu some of the interdune areas contain extensive clay flats. The Lantewa and Gudumbali Dunefields are separated by a complex sand ridge called the Bama Ridge. This Ridge stands as much as 12 m (40 ft) above the surrounding plains and runs from east of Geidam, through Maiduguri and Bama, to the Cameroon frontier. It has also been mapped in the Niger and Chad Republics and marks an old shoreline of Lake Chad. A sand plain lying between the beach ridge and the dunes further east is interpreted as a former beach when Lake Chad was considerably larger than it is at the present time.

East of the sand plains and dunefields the area is dominated by the Yedseram and El Beid rivers which flow north from the Mandara Mountains to Lake Chad. The upper reaches of the El Beid are in Cameroon Republic. In its upper reaches the Yedseram flows over the gently undulating Uba Plains, which descend gradually from over 600 to 300 m (2 000 - 1 000 ft) east of Damboa and are more typical of the Basement plains of the southern part of the project area. North of the boundary between the Basement rocks and the overlying Chad Formation the Bama Deltaic Complex extends as far north as Dikwa. This Complex consists of extensive clay and sandy plains with very little relief. South of Bama it contains both the present and older, more extensive, floodplains of the Yedseram river. North of Bama neither the Yedseram nor its major tributary, the Ngadda, reach Lake Chad. They disperse between the Bama Ridge and the present shoreline of the Lake over virtually flat plains. In the Bama Deltaic Complex these plains consist of a very complex association of deltaic deposits formed when Lake Chad extended to the Bama Ridge. East of Bama and north of Maiduguri, on the edge of the Gudumbali Dunefield, these deltaic deposits have partially buried relics of the longi tudinal dunes. North and east of Dikwa this complex of deltaic plains gives way to extensive flat clay plains - known locally as 'firki'. These are the plains of the Chad Lagoonal Complex and they owe their form to clays deposited during lagoonal conditions of a more extensive Lake Chad. The present border of Lake Chad is marked by a series of undulating sand plains grouped as the Chad Lacustrine Plains. In the north these plains consist of a series of low sand ridges parallel to the present shoreline; further south small clay depressions occur within the sand plain and its border with the Chad Lagoonal Complex is marked by a small but distinct beach ridge.

The Gongola and its tributaries form the major river system in the southern part of the project area. The Gongola rises on the Jos Plateau from where it flows northeast across the Bauchi Plains, west of the survey area, and through the Kerri Kerri Plateau as far as Nafada; it then swings abruptly south and flows through the main Gongola Valley to join the Benue opposite Numan. The Gongola Valley is cut mainly in Cretaceous sediments, although Basement rocks are exposed at Kaltungo and to the east of the Gongola between it and the Biu Plateau. The Valley con tains flat and undulating plains descending gradually from 430 m (1 400 ft) southwest of Damaturu to 180 m (600 ft) north of Numan where they merge with the plains of the Benue Valley. The various plains are separated by hill ranges which in some places rise abruptly to over 300 m (1 000 ft) above the surrounding plains. These ranges are formed on both sandstones and Basement Complex rocks and there are many prominent single hills formed by volcanic plugs or cones. In the southern half of the Valley, where the Gongola cuts through folded Bima Sandstone, these hills form some of the most spectacular scenery in Nigeria.

West of the Gongola Valley the Kerri Kerri Plateau forms extensive rolling upland plains between 300-600 m (1 000 - 2 000 ft), with occasional upstanding flat-topped ironstone-capped relic hills. North of the Gongola the Plateau drains to the Gongola itself; to the south most of the Plateau is drained south by the river Pai to the Benue. The Pai and its major tributaries have flat-floored incised valleys bounded in most places by steep sides rising to

44 the more gentle Plateau slopes. In several places the escarpment, which bounds most of the Plateau, is dissected into a series of steep flat-topped ridges and flat-floored valleys. A similar dissected escarpment borders the Potiskum Plain southeast of Potiskum.

North of the Hawal river the eastern border of the Gongola Valley is marked by steep hills and an escarpment rising between 150-300 m (500 - 1 000 ft) to the Biu Plateau. The Plateau consists of a series of gently sloping basaltic plains between 600 and 850 m (2 000 - 2 800 ft) above sea level.

North of Biu itself groups of steep conical hills, formed from extinct volcanoes, rise between 60 and 150 m (200-500 ft) above these plains. The escarpment continues south and east of Biu. South of Buni however it is less marked and only a low scarp marks the boundary with the Biu Plains. The Biu Plains consist of a series of flat or gently sloping plains descending gradually from 600 m (2 000 ft) adjacent to the Biu Plateau to 450 m (1 500 ft) on the border with the Uba Plains.

The Uba Plains are drained by both the Hawal and the Yedseram river systems and in the south some areas are drained by the Kilunga which flows through the Gaanda Hills to the Benue. They consist of a series of gently undulating partially dissected plains between 600-300 m (2 000 - 1 000 ft) above sea level. The plains are underlain by rocks of the Basement Complex; their general uniformity is broken in several places by groups of spectacular inselbergs rising abruptly 150-300 m (500-1 000 ft) above the surrounding country. At Hong (between Gombi and Mubi) the highest peaks reach 1 300 m (4 300 ft). Most of these inselbergs are associated with Older Granites.

South of the Hawal river the border between the Uba Plains and the Gongola Valley is marked by the Gaanda Hills which form a strongly dissected escarpment zone extending south from the Biu Plateau. Further east this hill range separates the Uba Plains from the lower-lying plains of the Benue Valley. The hills extend into the Cameroon Republic and, northeast of Song (at Zummo), they contain mountains with summits over 1 000 m (3 300 ft) which are similar to those in the Mandara range.

The eastern part of the project area between Bama and Mubi is occupied by the Mandara Mountains. In the north this mountain range extends eastwards more than 50 km (30 mi) into the Cameroon Republic and outliers of these mountains form hills west of Maroua (see Text Map 1). Further south the mountains are confined to a narrower band. The frontier between Nigeria and the Cameroon Republic runs through the Mandara mountain range: only those hills and mountains in Nigeria are considered here. The highest summits rise steeply from the footslopes to over 1 200 m (4 000 ft). The footslopes themselves rise steadily from 450 m (1 500 ft) in the north adjacent to the Bama Deltaic Complex to 600 m (2 000 ft) at Mubi adjacent to the Uba Plains. They extend eastwards into the mountains where they occur in narrow valleys and are in some areas deeply eroded. The mountains themselves contain several areas of more gentle relief between the altitude of the footslopes and the summits.

The south of the survey area lies in the Benue Valley and consists of a series of gently undulating plains rising from between 90-155 m (300-500 ft) along the Benue river itself to 150-240 m (500-800 ft) adjacent to the Kerri Kerri Plateau, the Longuda Plateau and the Gaanda Hills. These plains are flanked by steep-sided sandstone hill ranges which follow the general east-west trend of the Valley and in places rise as much as 450 m (1 500 ft) above the plains. The Longuda Plateau lies between the Gongola Valley and the Benue Valley 700 m (2 300 ft) above sea level. It consists of undulating Basalt plains, similar to the Biu Plateau, bounded on all sides by an escarpment. It is however more dissected than the Biu Plateau. East of Yola sandstone hills have confined the width of the floodplain of the Benue to less than 500 m (550 yd). West of Yola, away from the hills the floodplain is very much wider and varies on the north bank alone between 3 and 12 km (2-7.5 mi).

45 GEOLOGY by M G Bawden

There are six major groups of rocks in the survey area each of which contains several different rock types. The distribution of these rock types is summarised on Text Map 9 and is shown in more detail, in association with the landform distribution, on Map 2. The geological succession is summarised in Table 1.

TABLE 1 GEOLOGICAL SUCCESSION

Group Rock type Formation Age VI 18 Recent alluvium Recent

17 Ancient alluvium

16 Lacustrine sands

15 Lagoonal clays Chad Quaternary V 14 Deltaic sands and clays

13 Beach sands and gravels

12 Aeolian sands

11 Consolidated sands and clays

10 Pyroclastic rocks IV Tertiary - Recent 9 Basalt

8 Continental sandstones with III Kerri Kerri Tertiary grits and clays

7 Sandstone (continental facies) Gombe and Gulani

6 Clays and shales with thin Fika, Pindinga, limestones (marine facies) Numanha, Sekule, Jessu and Dukul Cretaceous II 5 Sandstones and shales with thin limestones (transitional facies) Yolde and Gongila

4 Coarse feldspathic sandstones (continental facies) Bima and Yola

3 Granites Younger Granites Jurassic

I 2 Granites Older Granites Basement Lower Palaeozoic 'Complex - Pre-Cambrian 1 Metasediments, gneiss and migmatite 46 GEOLOGY TEXT MAP 9

SCALE 1:3,000,000

25 50 75 100 MILES

10°

^rr: Group Rock Type Formation Age VI J I,1 Mil! 18 Recent alluvium Recent Outside 17 Ancient alluvium project area /,/ 16 Lacustrine sands 1MM1 15 Lagoonal clays V 14 Deltaic sands and clays Chad Quaternary

1 3 Beach sands and gravels

12 Aeolian sands 111! 1 1 Consolidated sands and clays 10 Pyroclastic rocks IV Tertiary-Recent Structural Trend 9 Basalt tök o Continental sandstones with III Kerri Kerri Tertiary Geological Boundary grits and clays .mi,«.:"1!!' 7 Sandstone (continental facies) Gombe and Gulani Q Clays and shales with thin Fika. Pindinga and Numanha, limestones (marine facies) II Sekufe. Jessu and Dukul Cretaceous Main Road e Sandstones and shales with thin ","»',". limestones (transitional facies) Yolde and Gongila 4 Coarse felspathic sandstones Railway (continental facies) Bima and Yola 3 Granites Younger Granite Jurassic International Boundary. +• +• t- + + + 1 •Hi 2 Granites Older Granite -, BaS(.menc Lower Palaeozoic - 1 Metasediments, gneiss and J Complex pre Cambrian migmatite

10° 12° East of Greenwich 14° Specialist information compiled by M. G. Bawden D.O.S. (LR) 3064U Drawn and photographed by Directorate of Overseas Surveys 1971 Copyright reserved Printed by the Ordnance Survey 7/7//J325/OS The information shown on these maps and in Table 1 has been obtained from several sources. The earliest overall description of the geology of northern Nigeria was made by Falconer (1911). Within the project area detailed mapping by the Geological Survey has been confined to the Gongola Valley and its immediate surroundings (Carter et al 1963). Du Preez (1949) described the geology of the Biu Division and Jones (1959a, b, and c; 1960) described the sediments in the area of the Benue Valley south of the Gaanda Hills, but published no maps. More recently Dousse (1969) has mapped the sandstones underlying the Potiskum Plain and the Kerri Kerri Plateau and Dessauvagie (1969) has described the geology of the extreme southwest of the project area between Bashar and the Benue river. Most of the geological investigations of the Chad Formation have been related to the hydrogeology of the Chad Basin and borehole records provide a considerable amount of information on the stratigraphy of the Nigerian portion of the Chad Basin and the sequence of pre-Quaternary rocks which underlie the Chad strata. The 1:2 000 000 scale geological map of Nigeria (1964) covers all the North East project area and there are maps and reports for Cameroon and Niger covering their common frontiers with Nigeria. This information, together with airphoto interpretation and ground observations made during the present investigation and observations recorded during several soil investigations, has been combined to provide a regional picture of the geology of the project area.

ROCK TYPES

Group I. Igneous and Metamorphic Rocks, Mainly of the Basement Complex The Basement Complex includes the oldest known rocks in Nigeria. It consists of scattered remnants of highly metamorphosed sedimentary rocks (type 1) and diverse, predominantly granitic, plutonic masses collectively known as the Older Granites (type 2). In the project area the Basement Complex is composed mainly of gneisses, migmatites and granites. These Basement rocks have been described and mapped in the Gongola Valley and south of the Benue river by Carter et al. (1963) and in the Jos Plateau area adjacent to the Bauchi Plains (west of the project area) by MacLeod et al. (1966). The occurrences over the remainder of the North East project area are only sparsely documented, but the Basement throughout northern Nigeria shows considerable uniformity in its gross characteristics and the descrip tions for areas which have been studied systematically can, in general terms, be extended to cover the whole area with reasonable confidence. Type 1. Metasediments, gneiss and migmatite The metasediments of the Basement Com plex are a group of highly metamorphosed sedimentary rocks consisting mainly of gneisses and migmatites. Areas of schist and quartzite also occur and small occurrences of amphibolite, gabbro and pegmatite are widely distributed. These metasediments have only a scattered dis tribution in the Gongola Valley; airphoto evidence suggests that they are more extensively developed in the Uba Plains, but there has been no systematic mapping in this area.

Type 2. Granites (Older Granites) The oldest rocks of the Basement Complex have been subjected to at least two major orogenic cycles (Oyawoye, 1964). Rocks of the Older Granites suite were formed during the second cycle, which extended from late Pre-Cambrian to lower Palaeozoic (Jacobson et ai.,1963). The Older Granites show all stages of granitisa- tion and magmatic activity. They have a considerable range in structure, texture and miner alogy and their contact relationships with the metasediments are very variable. In the Gongola Valley, where the Older Granites have been studied in detail by Carter et al. (1963), the most extensive rocks are equigranular and coarse porphyritic granites. They are characteristically rich in potash and range in composition from granite to granodiorite. Similar rocks have been described from the Mandara Mountains in Cameroon (Gazel et al., (1956; Koch, 1959) and the Mandara Mountains in Nigeria are believed to consist largely of Older Granites (Nigeria Geol. Surv., 1964). The distribution of Older Granites between the Gongola Valley and the Mandara Mountains, where they form the more massive inselbergs in the Gaanda Hills and on the Uba Plains, is based mainly on airphoto interpretation done during the present investigations.

Type 3. Granites (Younger Granites) West of the project area granitic massifs are developed over a wide area in the Jos Plateau region (Jacobson et al., 1958). These massifs are composed of a wide variety of medium to coarse-grained granites together with syenite, gabbro and rhyolite. They are discordantly intruded into the Basement Complex with sharply defined contacts which cut across these older rocks. They are of mid-Jurassic age (Jacobson et al., 1963) and are collectively termed Younger Granites. Granites which can definitely be included in this group outcrop only in the extreme northwest of the project area near Matsena. In the Gongola Valley Carter et al. (1963) describe a group of granites, porphyries and lavas which intrude the Older Granites west of the confluence of the Hawal 49 and the Gongola. They do not however contain the suite of rocks or the structures characteristic of the Younger Granites elsewhere. They are grouped with the Younger Granites simply because they are granitic and are demonstrably younger than the Older Granites.

Group II. Cretaceous Sedimentary Rocks Cretaceous sedimentary rocks lie unconformably on the Basement Complex in both the Benue and Gongola Valleys. They are believed to have been deposited in a rift valley which approxi mately followed the present alignment of the two valleys (Wright, 1968). Similar sediments overlie the Basement Complex northeast of the Biu Plateau, and have been recorded in bore holes as far north as Maiduguri under the Chad Formation. The details of the succession are understood better in some areas than in others. The Gongola Valley and parts of the Benue Valley have been mapped and described in detail (Carter et al., 1963). The western part of the Benue Valley has been mapped photogeologically by Dessauvagie (1969) and Jones (1959 a, b, and c; 1960) has described the sediments in the Benue Valley east of the Gongola river. No detailed mapping has been done in the area northeast of the Biu Plateau and the informa tion presented here is derived largely from soil investigations by Carroll and Klinkenberg (personal communications). The oldest Cretaceous sediments are continental in character and consist of coarse-grained false-bedded feldspathic sandstones (type 4), of which the Bima Sandstone is the most impor tant and the most extensive member. The younger sediments are more complex in character; in general the rocks consist of sandstones and shales (type 5), which are transitional in character between the continental conditions and the subsequent marine conditions, overlain by marine clays, shales and limestones (type 6). These marine strata are overlain by a further series of continental deposits (type 7) consisting of estuarine and deltaic sand stones and silt stones of which the Gombe Sandstone is the most extensive.

The Cretaceous sediments were laid down in the Benue and Chad Basins. These were separated by a ridge of Basement Complex rocks on which the sediments are less thick than elsewhere. This ridge - known as the Zambuk Ridge - now lies on a line roughly from the Biu Plateau through Gombe to Kaltungo along which inliers of Basement rocks are exposed (see Text Map 9 and Figure 6a). Because of this division into two separate areas of deposition and the changes from initial continental conditions to marine conditions and back to continental conditions, the sequence of Cretaceous strata is different in different parts of the survey area and rocks of very different composition may be the same age. Type 4. "Coarse feldspathic sandstones.icontinental faciesj(Bima and Yola),The Bima Sandstone is the oldest and most extensive of the Cretaceous sediments. It consists of massive coarse false-bedded sandstones resting unconformably on rocks of the Basement Complex. It was derived largely from the erosion of these rocks. The lower beds are invariably felds pathic but the higher beds generally contain less feldspar. The false bedding and diverse lithology of the Bima Sandstone indicate that it accumulated under widely varying continental conditions. Evidence of fluviatile and deltaic conditions is given by many cross-bedding structures, and the massive white and purple clays which are included within the sandstones are probably of lacustrine origin. The Bima Sandstone is thickest in the Lamurde anticline, in the Benue Valley. The bottom of the succession is not exposed but its total thickness is probably more than 3 000 m (9 800 ft). East of the Song-Yola road sandstones which are indistinguishable from the Bima Sandstone occur throughout the sequence and show that in this area continental conditions of deposition continued throughout the Cretaceous. Jones (1959 (c)) defined these Bima-type sandstones, which are comparable in age with the transitional and marine sediments, as Yola Sandstone.

Type 5. Sandstones and shales with thin limestones, transitional facies (Yolde and Gongila) Over most of the area in the Benue Valley, apart from the extreme east beyond the Song-Yola road, and in the Gongola Valley, the continental conditions of the Bima Sandstone were followed by marine conditions. The sediments which mark the change consist of a very variable sequence of sandstones and shales with thin limestones defined as the Yolde Forma tion. North of the Zambuk Ridge a similar transitional phase is marked by 450 m (1 480 ft) of limestones and shales with some sandstones defined as the Gongila Formation. Small areas of similar transitional sediments occur in the Damaturu Plain east of Damboa and further south in the Uba Plains but they have not been investigated in any detail.

50 Type 6. Clays and sandstones with thin limestones, marine facies (Pika, Pindinga, Numanha, Sekule Jessu and Dukul) A conformable sequence of about l ooo m (3 300 ft.) of marine strata overlies the transitional Yolde Formation south of the Zambuk Ridge. These marine strata are assigned to four Formations (Carter et al., 1963):

4. Numanha Shales - shales with occasional bands of sandstone, nodular mudstone and limestone;

3. Sekule Formation - shales with thin bands of limestone;

2. Jessu Formation - alternating sequence of shales and sandy mudstones with thin sandstone horizons;

1. Dukul Formation - shales and thin limestones.

Further north in the Gongola Valley, in the area of the Zambuk Ridge, the marine strata overlying the Yolde Formation consists of 200 m i(650 ft)1 of shales with thin limestones at the base, which have been defined as the Pindinga Formation. East of Nafada the change from the transitional conditions of the Gongila Formation to the marine conditions represented by the Pindinga Formation was gradual and irregular and the two Formations cannot be clearly differentiated. North of Nafada the marine deposits are blue-black shales, occasionally gypsiferous and containing one or two impersistent limestones. These are defined as the Fika Shales; their total thickness is not known but a borehole at Damagum proved a minimum of 430 m (1 400 ft).

Type 7. Sandstone, continental facies (Gombe and Gulani) North of the line of the Zambuk Ridge the marine strata of rock type 6 are overlain by 300 m (1 000 ft.) of estuarine and deltaic sandstones, siltstones, shales and ironstones. These were probably deposited in a basin which lay north of the Zambuk Ridge in the late Cretaceous. These strata are defined as the Gombe Sandstone (Carter et al., 1963) and are largely composed of siltstones or flaggy sandstones. They are soft and light grey when fresh, but on exposure give rise to dark red, flaggy debris which characteristically mantles the Gombe Hills. In the east of the Gongola Valley the marine Pindinga shales are overlain by at least 60 m (200 ft), of cross-bedded massive fine- and medium-grained sandstones which also represent a change to estuarine conditions. These rocks are probably the same age as the Gombe Sandstone but there is no evidence to suggest that they were deposited in the same basin. The fourfold sequence of marine strata in the south of the Gongola Valley and in the Benue Valley is followed by the Lamja Sandstone. This Formation outcrops over only a small area below the basalt on the eastern margin of the Longuda Plateau. It consists of fine-grained sandstones with thin, in some places carbonaceous shales; thin coal seams are exposed at two localities. Although exposed over a very small area the Sandstone represents a change to similar continental con ditions i._ at least part of the 3enue Basin as that which occurred further north in the region of the Zambuk Ridge and in the Chad Basin.

Group III. Tertiary Continental Sandstones Type 8. Continental sandstones with grits and clays (Kerri Kerri) The Tertiary sedimentary rocks within the project area consist of a sequence of flat-lying continental grits, sandstones and clays known as the Kerri Kerri Formation. They underlie the Kerri Kerri Plateau and the Potiskum Plain', to the north. A small outlier occurs in the Korode Escarpment northeast of the Biu Plains.

The Kerri Kerri Formation was deposited on an irregular post-Cretaceous land surface under a wide range of continental conditions. West of the Kerri Kerri Plateau it lies unconformably on the Basement Complex. In the east and south it lies unconformably on Cretaceous sediments; the westerly extension of these sediments underneath the Kerri Kerri Formation is not known. Lacustrine and deltaic sediments are the most frequently occurring strata in the Kerri Kerri Formation. There are similarities in lithology and sedimentary structures between the Kerri Kerri Sandstone and the Bima Sandstone, though the latter is characterised by the feldspathic content of its sediments and a very much coarser grade.

Information from drilling indicates that the total thickness of the Kerri Kerri Formation is not more than 300 m (1 000 ft) and that it does not extend far to the east and north below the Chad Formation (Dousse, 1969).

51 Geological Section Figure 6a

N 70' E

Gongoli River Bima Hill

4000' -,

2000'

Sea level

en to

N IIO'W N 110° E N 70^ w

Hawal River Askira Tedseram River

+ + + + + - 2000' Older + + + + + ++ + + + + + + ++ + ++ r : + Granite + T^>-< +> + v + + +v +"

Section from the Kerri Kerri Plateau east to the Mandara Mountains

DOS. 3099 F Geological Sections Figure 6b

N45°E N 135°w

Buratai Hawal River Halduguri Lake Chad

Basalt 2000' + + + + + + + + + + + Basement Complex + + + + + S«a l«v«l . + + + + + + + ++ + + + ++ + + + + + + + ++ + + + + +++++ +

1 Upper zone of aquifers 2 Middle 3 Lower •> •• >• en Section north-east from the Biu Plateau (Buratai) to Lake Chad

North South

Hawal River - Garkida Song Loko River Benue River

4000'

2000' ^Basalt B«..i. _-i^\ NAA v u •> ^^^^^ Basalt "+"""+i + r^- S \ Yolde f* ^ ^> j. '4. + +T + + + + ' + +" + [V ___-—<—-__formation / + + +V + + + Basement Complex* V+J+^anlt'e+tl+^r^^ + + + + + + + + + + + + +++ + ! + + + + +| + + +++ + +>^_ Sandstone

Section south from the Biu Plateau (Ngulde) to the Benue River (Yola)

D.O.5. 3099 G spm,^

PLATE 1/1 Song. View from basalt hill across farmland with Adansonia digitata and Acacia albida. Typical inselbergs in the background.

PLATE 1/2 Biu Plateau. General view northwards from Tilla Lake with cones and craters in the far distance. 54 PLATE 1/3 The Kadi Escarpment.

PLATE 1/4 Near Pindinga. Exposure of Pindinga shale in river bank in predominantly Gombe Sandstone, Land System IIb7, the Gombe Plains. 55 Group IV. Tertiary to Recent Volcanic Rocks

Volcanic rocks are widely distributed in the southern part of the survey area. They occur as volcanic plugs in the Benue Valley and in the southern part of the Gongola Valley, and as basaltic lavas forming the Biu and Longuda Plateaux and other smaller complex lava flows of which the Song Volcanic Complex is the largest. The age of this volcanic epoch has not been precisely determined but it seems likely that it extended from the mid-Tertiary to Recent (Carter et al., 1963).

The distribution of the volcanic plugs is irregular and they do not appear to be associated with any tectonic lines. They cut all formations of the Cretaceous succession but have not been seen to intrude the Kerri Kerri Formation or later rocks.

Type 9. Basalt The Biu Plateau and the Biu Plains are underlain by extensive flows of olivine basalt. These basalt flows were extruded spasmodically over a considerable period of time and the total thickness is made up of several flows. On the west of the Biu Plateau the total thickness is less than 30 m (100 ft ) (Carter et al., 1963), but further east du Preez (1949) estimated a total thickness 'in the order of 300 m (1 000 ft)' . The basalts are fine-grained, dense, olivine-bearing rocks. The various flows show little variation in appearance or composition. There is no satisfactory evidence to show their mode of erup tion; no parent vents have been identified and there is no indication that they were extruded from fissures. The lavas were very fluid and thin flows extend over wide areas.

The Longuda Plateau is more dissected than the Biu Plateau and is much smaller, but it is capped with similar dominantly fine-grained olivine basalts. They are flat-lying and attain their maximum development in the eastern part of the plateau where they are 300 m (1 000 ft ) thick (Carter et al., 1963). In many localities around the escarpment edge to the plateau individual flows can be readily identified; the variation in thickness of these flows seems to be controlled largely by the pre-basalt topography. Like the Biu basalts, there is no evidence of either the mode of eruption or the precise age of the Longuda lavas. No parent vents or fissures have been located and there is no evidence to suggest that the Biu and Longuda basalts were derived from a common source.

Similar but smaller areas of volcanic rocks, consisting mainly of olivine basalt flows, with small quantities of pyroclastic rocks, occur immediately to the south of the Biu Plateau at Garkida and further south in the vicinity of Song and Kuma. They have also been recorded (Nigeria Geol. Surv., 1964) in small areas within the Mandara Mountains, but their distribu tion has not been mapped in detail and they are omitted from the maps accompanying this account.

Pine-grained olivine basalts also form the majority of the volcanic plugs which are wide spread in the south of the Gongola Valley and in the Benue Valley. More than 300 have been mapped (Carter et al., 1963) varying in size from small mounds a few meters high to towering conical hills rising more than 300 m (1 000 ft ) above their surroundings. They are most numerous south and west of Kaltungo where one of the best known peaks formed by a volcanic plug is Tangale peak, the summit of which reaches 1 300 m (4 260 ft ), some 600 m (2 000 ft ) above the surrounding Bima Sandstone.

Type 10. Pyroclastic rocks There are several well preserved volcanic vents and craters on the Biu Plateau which are composed of a variety of pyroclastic rocks (du Preez, 1949). The cones to the west of the Biu-Damaturu road are composed of decomposed scoriae, fragments of ropy lava, bombs, tuffs and agglomerates which contain boulders of granite- gneiss. Agglomeratie tuffs form aprons around the cones west of Meringa and agglomerates consisting chiefly of lava bombs form many cliffs and crags. Ultra-basic nodules are an important component of the agglomerates in some areas. Small basalt lava flows and mud flows occur with these pyroclastic rocks in several places on the Plateau.

Similar but much less extensive areas of pyroclastic rocks occur in the Song Volcanic Complex but have not been mapped.

Group V. Quaternary Sediments of the Chad Formation Quaternary rocks within the project area are mapped by the Nigeria Geological Survey (1964) as one formation - the Chad Formation. As mapped, the Formation includes a wide range of consolidated lacustrine and fluviatile sands and clays overlain by unconsolidated largely wind-blown sands and a wide range of alluvial, deltaic and lagoonal sediments. The consoli dated sediments have been described by Barber (1965). Higgins et al. (1960) and Pullan (1964) have described the unconsolidated superficial deposits. These superficial deposits

56 are closely related to the present landforms and to the recent evolution of the Chad Basin; as they are therefore discussed in more detail below under 'Geomorphology' , their lithological characteristics are only briefly described here.

Type 11. Consolidated sands and clays (Chad) Consolidated sediments of the Chad Formation are exposed beneath thin superficial deposits southwest of Maiduguri and south and west of Damaturu. In the latter area they overlap Cretaceous rocks in the Gongola Valley and outliers of the oldest Chad strata have been recorded by Carter et al. (1963) as far south as Nafada. North of the Potiskum Plain Chad strata overlap the Kerri Kerri Sandstone and further west they overlap the Basement rocks underlying the Bauchi Plains. The boundary with these older rocks has been mapped by Schroeder (Nigeria Geological Survey, unpublished map 1969).

Elsewhere in northeast Nigeria the consolidated sediments of the Chad Formation are covered by more recent unconsolidated deposits; there are no exposures of the consolidated sediments and their distribution and lithology is known only from the evidence of boreholes.

These Chad strata consist of a complex series of lacustrine and fluviatile clays and sands. They show considerable lateral variation both in thickness and in composition, but a general threefold .sequence of a thick clay series overlain and underlain by somewhat clayey arenaceous series has been recognised over a wide area (Barber, 1965). These strata have very gentle regional dip northeast below Lake Chad, but in any one locality they are more or less horizontal. In the Gongola Valley the Chad sediments vary in thickness from a few meters to 120 m (400 ft ). Near Maiduguri they are 550 m (1 800 ft ) thick; further east they increase to about 600 m (2 000 ft ).

Type 12. Aeolian sands (Chad) North of a line from Azare through Maiduguri to Mongonu the near-horizontal strata of the Chad Formation are overlain by unconsolidated pre dominantly aeolian (wind-blown) sands. The sands form extensive hummocky plains in which are developed two main groups of sand dunes. These sand plains and dunefields are part of the ancient erg of Hausaland (Grove, 1958) and are related to the former extent of desert condi tions. North and east of Maiduguri the sands are partially buried by more recent deltaic and lagoonal deposits (rock types 14 and 15). The origin of these sands is not clearly under stood. Pullan (1964) has suggested a fluvial origin with subsequent wind action at two separate stages forming the two main groups of dunes.

Type 13. Beach sands and gravels (Chad) There are two groups of sands and gravels which form distinct complex ridges and are interpreted as former beach ridges of Lake Chad (Grove and Pullan, 1963). The larger and older is the Bama Ridge which extends from east of Geidam, through Maiduguri and Bama to the Cameroon frontier. Du Preez (1949) and Barber and Jones (1960) record a range in composition from coarse sand and gravel through grit and fine sands to silts. Pullan (1969) showed that fine to medium sands predominate and suggested that the coarse gravels are confined to the core of the ridge. A smaller more recent ridge, composed mainly of rounded sands and known as the Ngelewa Ridge, runs from west of the El Beid river through Gambaru to Mongonu.

Type 14. Deltaic sands and clays (Chad) East of Maiduguri aeolian sands of type 12 are overlain by an extensive very variable succession of sands and clays. These were laid down in a series of successive deltas formed by rivers flowing north from the Mandara Mountains. The deposits occur in both ancient, now largely abandoned, deltas associated with previous courses of the river system which flowed into Lake Chad when it extended to the Bama Ridge, and in smaller more recent deltas formed by the present rivers which flow through the Bama Ridge but do not reach the Lake.

Type 15. Lagoonal clays (Chad) North and east of Dikwa the deltaic deposits of type 14 pass laterally into greyish brown and black clays, known locally as 'firki' . In some places the clays are laminated and have the characteristics of a shale. Calcium carbonate concretions are abundant in the brown clays; the darker clays have a strong polygonal macro- structure and are believed to contain a high percentage of montmorillonite (Pullan, 1964). These clays were deposited under lagoonal conditions associated with the previous greater extent of Lake Chad. In some areas deposition seems to be continuing at the present time, mainly due to river flooding (Klinkenberg, personal communication).

Type 16. Lacustrine sands (Chad) The present shore of Lake Chad is bounded by uni form medium to fine sands. In the north they form a complex series of parallel beach dunes; further south the predominantly fine aeolian sands are associated with alluvial silts, loams and clays. 57 Type 17. Ancient alluvium (Chad) In the north of the project area both the sand plains and the dunefields are overlain by alluvial sands and clays related to former courses of the Yobe river and its tributaries. In several areas these sands and clays have been partially re-sorted by wind action and are now associated with, or overlain by, aeolian sands from the adjacent sand plains and dunefields. South of the Bama Ridge alluvial sands and clays from the Yedseram form extensive spill plains and terraces over rocks of the Chad Formation and the Basement Complex. East of Bama, on the Cameroon frontier, alluvial clays form spill plains associated with previous more extensive phases of the El Beid river system.

Some areas underlain by these ancient alluvial deposits are subject to occasional flooding at the present time and therefore also contain recent alluvium.

Ancient alluvial deposits are far less extensive in the southern part of the project area. Small areas of alluvial sands border the present floodplain of tributaries of the Gangola south of Shellan, and there are areas of older alluvial deposits bordering the present floodplains of the Loko river south of Song. In the Benue Valley Carter et al. (1963) mapped an extensive series of piedmont deposits consisting of ancient alluvial sands and clays which they grouped together as Benue Valley Alluvium. Klinkenberg (1967) showed that some of these sands and clays were developed in situ from Cretaceous sediments and that older alluvial deposits associated with the Benue are more limited in extent (see Map 2).

Group VI. Recent Alluvium Type 18. Recent alluvium This alluvium occurs along most of the water courses in the project area. It ranges in extent from thin discontinuous sands occurring in the smallest streams to thick broad alluvial sands and backswamp. clays of the Gongola, Benue, Yedseram and Yobe rivers.

Structure The Older Granites and associated granite gneisses of the Basement Complex have a well developed and generally widely spaced pattern of rectangular jointing. In general joints are better developed in these granitic rocks and in the quartzites than in the other metasediments. As a group the metasediments present a remarkably uniform series of strongly foliated rocks; in detail the structures are very complex and there is evidence that they have been folded more than once.

The major structural trends in northeast Nigeria have been determined by earth movements immediately preceding and following the deposition of the Cretaceous sediments. The struc tural pattern within the Cretaceous rocks is dominated by a series of long, narrow and relatively simple folds (see Text Map 9). The Tertiary and younger strata are virtually flat-lying and, although downwarped towards the northeast, are unaffected by folding or faulting. The main structures in the Gongola Valley are summarised in Figure 6a, which also shows the relations of the other rock types on either side of the Valley. Figure 6b sum marises the relation of the various rock types northeast and south of the Biu Plateau.

Various workers (e.g. Pugh and King, 1952) have suggested that the Cretaceous sediments in the Gongola and Benue Valleys were deposited in troughs resulting from rift faulting of the Basement rocks. This early Cretaceous rift faulting was associated with the separation of South America from Africa during the breakup of Gondwanaland (King, 1950). Rift faulting was supported by Cratchley and Jones (1965) who suggested that the main faults are buried by the Cretaceous sediments.

The main late Cretaceous folds in the Gongola Valley are the Kaltungo and Bima anticlinoriums and the Gulani synclines. The Kaltungo anticlinorium is the largest structural unit and embraces complicated folds between the Kaltungo Basement inlier and the Basement south of the Biu Plateau. At Kaltungo the strata form a broad northeast trending anticlinal structure with the Basement inlier at its core. East of the inlier this structure divides northeast wards and passes into a series of separate anticlines and synclines. These folds are characteristically asymmetrical, showing steeper dips along their northern limbs. The main component of the Bima anticlinorium, the Bima anticline, plunges west near Zambuk. The inlier near Gombe represents part of this fold repeated by faulting (Figure 6a). Later sub sidiary folds with a north-south trend are superimposed on the Bima anticline. North of the Bima anticlinorium the fold pattern is predominantly north-south and consists of a series of comparatively small basin-shaped folds which owe their prominence to the resistance of the Gulani Sandstone. North and east of Nafada the folds have a southeast trend.

58 The Cretaceous rocks south of Damboa are not well exposed and their structures have not been investigated. However, airphoto evidence suggests that the general east-west strike is con tinued. No major fold areas have been identified and, compared with the scale of folding in the Gongola Valley, the strata seem to be only gently folded.

The Benue Valley is characterised by long asymetrical folds of which the Lamurde anticline is the most important and extends for nearly 95 km (60 mi) southwest from the Longuda Plateau. It is flanked on the north by the Dadiya syncline and on the south by the Benue syncline which is largely masked by alluvial deposits from the Benue. The general northeast trend of the Lamurde anticline is continued by similar but shorter folds south of Bashar (Dessauvagie, 1969) and east of the Gongola between Yola and Song.

There is evidence that the earth movements responsible for folding the Cretaceous sediments to some extent preceded the deposition of the youngest strata. The gentle folding of the Gombe Sandstone contrasts with the strong folds imposed on the older rocks and, although no unconformity has been detected between the Gombe Sandstone and the underlying formations, the Gombe Sandstone seems to post-date the main period of folding in the region.

Faulting, which mainly took place after the folding, has affected all the Cretaceous rocks in the Gongola Valley. Two classes of faults have been recognised (Carter et al., 1963): strike faults, which are best developed in the vicinity of the Zambuk Ridge, and tension faults which occur at the margins with the Basement. At least two periods of faulting have been recognised; early faults with easterly trends are truncated or offset by later northerly trending fractures. Faults are less common in the Benue Valley and the major folds are largely undisturbed by faulting.

The structural pattern in the Cretaceous rocks shows that the major compressional stresses operated from the north and south whilst subsidiary stresses took place at right angles to this. Wright (1968) suggested that the folds were a result of compression which followed the tensional rift faulting. "When Africa and South America finally separated, the southern half of Africa tended to swing back, so that the hitherto stretched Benue trough region was transformed into a minor compressional belt, folding the sediments with it' .

59 GEOMORPHOLOGY by M G Bawden

Over most of northeast Nigeria there is a close relation between the landforms and the under lying rocks observable both at the regional scale of the major relief units (Text Map 2) and at the more detailed larger scale. Indeed, it is this close relation between the shape of the land, the rock types and the soils derived from those rocks which makes possible the extensive use of aerial photographs in mapping the land resources. As has already been men tioned this close correlation between relief, rock type and the soils derived from them is also the basis for the land system classification which is described in Volume 3 of this study.

The landform of the major relief units has been briefly described under Physiography and the rock types have been described under Geology. The purpose of this Geomorphology section is twofold; first to describe the landforms and their association with the main rock types and second to suggest the probable sequence of development of the present landscape.

The distribution of the landforms and the rock types with which they are associated is shown on Map 2. Because associations of landforms are closely related to the 6 major groups of rock types, the landforms are described under the same group headings as those used in the Geology chapter. The soils are described under similar headings for the same reason.

Landforms Developed on Rocks of Group I: Igneous and Metamorphic Rocks, mainly of the Basement Complex The general pattern of landforms developed on Basement Complex rocks is simple. The pattern is more complex in the hilly areas than in the plains, but in both the number of different landforms is small. In detail the wide variety in lithology of the Basement rocks results in a considerable variation in their resistance to erosion, and there are many minor changes in landscape throughout the Basement plains which can be directly related to this variation in lithology.

The migmatites and gneisses (rock type 1) generally underlie more or less dissected undulat ing or gently undulating to flat plains. The relief is fairly uniform with only occasional hills rising above the level of the gently sloping interfluves. Upstanding areas which do occur in these plains are generally isolated rocky hills (inselbergs) or low elongated ranges often with a serrated outline. The orientation of these low ranges usually follows quartzite ridges, dykes or fault lines.

North and northwest of Mubi the Basement plains are underlain by extensive areas of ironpan. In many places the ironpan is exposed in the break of slope to the streamlines and the interfluve is bounded by a distinct scarp. Apart from the relatively gentle relief of the plains where ironpan is developed, the Basement plains are generally more dissected with straight gentle slopes descending from narrow interfluves to streamlines with only narrow' and impersistent floodplains. In many areas the interfluves are capped by ironpan and ironpan also forms rocky scarps in the valley-side slopes.

The Older Granites and other predominantly granitic rocks of type 2 are more commonly associated with hilly and highland areas. They form groups of inselbergs, massive steep- sided hills and mountain ranges. The Older Granites generally have a widely spaced, strongly developed pattern of rectangular jointing which controls the well developed rectangular drainage pattern. The highest summits in the generally rugged Mandara Mountains rise to over 1 200 m (4 000 ft) from the pediment slopes, which in turn rise steadily southwards from 450 m at Gwoza to 600 m south of Mubi (1 500-2 000 ft). Within the mountain range, between the pediment and the summits, there are areas of more gentle relief. These intermediate levels have not been fully investigated, but aerial photographs show that their general appearance is remarkably consistent throughout the range and contour maps (DOS series 430)

60 show that they occur at two levels: about 760 m (2 500 ft) and 900 m (3 000 ft). These levels are not controlled by lithological changes and they are therefore presumed to represent relics of successive planation surfaces, higher than the surface represented by the Uba Plains. Similar higher surfaces occur in the Zummo Mountains south of the Mandara range.

Summit levels in the Gaanda Hills are not as high as those in the Mandara Mountains. The Hills consist of groups of inselbergs between which are relics of more gentle terrain at the same altitude as parts of the Uba Plains, but higher planation surfaces have been recognised. The Hills contain large areas of bare rock and shallow stony soils and in general the regolith is thin and discontinuous. These Hills, extending from east of the Zummo Mountains near the Nigerian frontier to the escarpment bordering the Hawal river on the east of the Gongola Valley,represent a wide-stripped zone separating the planation surface of the Uba Plains from the more recent erosion cycles in the Gongola and Benue Valleys.

The granites and other igneous rocks grouped under rock type 3 also give rise to hills. The Younger Granites in the extreme northwest form isolated inselbergs which rise from beneath the surrounding sand plain. The granites, porphyries and lavas in the Gongola Valley form steep hills associated with the adjacent hill masses formed on Older Granites.

Landforms Developed on Rocks of Group II: Cretaceous Sediments The form of the plains underlain by Cretaceous sediments is closely related to the different resistance to erosion of the various rock types and the topography closely reflects the varying lithology and the geological structure. In general the clays, shales and limestones of the transitional and marine facies (rock types 5 and 6) are less resistant and therefore form lower-lying flatter areas. Many of the small hills, ridges and depressions within these areas are directly controlled by detailed variations in lithology. Plains are formed on sandstones of the continental and transitional facies (rock types 4 and 5) where they are only gently folded, but these plains generally show a greater range of relief and are more undulating than the clay plains.

The more strongly folded continental sandstones generally form steep-sided hill ranges, ridges or isolated more rounded hills. In the Benue Valley and the southern half of the Gongola Valley the hill ranges are composed largely of folded Bima Sandstone and sandstones of the Yolde Formation. The general east-west alignment of these ranges closely follows the structural trends of the main fold belts. Several of the hill ranges are asymmetrical with the steeper slopes coinciding with the steeper limbs of the folds. Further north in the Gongola Valley there are fewer hills and they stand less high above the adjacent plains. They are again closely related to the sandstone members of the folded Cretaceous strata. The smaller number and reduced size of the hills generally reflects the less intense folding which has affected the area. The form of the Gulani hills closely follows the north-south fold axes in the Gulani Sandstone. Further north the Bima Sandstone forms both hills and undulating plains and again the distinction seems to depend on the intensity of the folding. Folded Gombe Sandstone forms hills along the western border of the Gongola Valley adjacent to the Kerri Kerri Plateau. In some areas on the southern margin of the Plateau, hills are related to structural trends in the Gombe Sandstone which can be clearly distinguished on the aerial photographs beneath a thin cover of Kerri Kerri Sandstone.

Landforms Developed on Rocks of Group III: Kerri Kerri Sandstone Kerri Kerri Sandstone underlies both the Kerri Kerri Plateau and the Potiskum Plain to the north of it. The Plateau consists of undulating to gently rolling plains 300 -600m (1 000 to 2 000 ft) above sea level. The drainage pattern is widely spaced with streamlines as much as 1.6km (1 mi) apart. In the north tributary streams flow in narrow V-shaped valleys to the floodplain of the Gongola. Further south the Pai and its major tributaries have flat-floored valleys bounded in most places by steep sides rising to the more gentle Plateau slopes. Throughout the Plateau the gentle upper slopes are straight or smoothly convex with only occasional small low hills and mesas standing above the otherwise uniform interfluve level. In the northern half of the plateau a linear pattern of north-south orientated low undulations can be distinguished on aerial photographs. These undulations have not been investigated in detail on the ground, but they are most likely to be relic dunes.

61 In some areas the Plateau is bounded by a high escarpment dissected into a series of steep flat-topped ridges and flat-floored valleys. This escarpment form is due to the easy erodi- bility of the sandstone. Elsewhere the Plateau is bounded by a more gradual descent, marked by a break of slope but without a distinct escarpment. This more gentle descent is complicated in the east by sandstone hills on the edge of the plateau.

The Potiskum Plain is flat to very gently undulating and descends gradually northeastwards from 395-330 m (1 300- 1 100 ft). Drainage lines are widely spaced in broad, partially drift-filled shallow valleys. The Plain is formed over virtually flat-lying Kerri Kerri Sandstone on which ironpan has been extensively developed. Southeast of Potiskum, near Kadi, it stands above the Kerri Kerri Plateau and is separated from it by a strongly dissected escarpment. Some parts of the escarpment face show as much as 10 m (33 ft) of ironpan over the unaltered sandstone. Ironpan cappings form small mesas east of Potiskum. Over the remainder of the Plain, ironpan and ferruginised sandstone form only scattered low scarps and there are only occasional hills. Similar mesas capped by ironpan occur between Damboa and Buni in the Korode Escarpment.

Landforms Developed on Rocks of Group IV: Volcanic Rocks Volcanic rocks occur as isolated plugs and extensive lava flows (rock type 9) and as pyro clastic rocks (rock type 10). Basalt plugs and cones occur mainly in the southern half of the Gongola Valley and in the Benue Valley. They are more resistant than the Cretaceous sediments into which they are intruded and therefore tend to form hill features. These vary from small dome-shaped hills a few meters high to towering conical hills rising more than 300 m (1 000 ft) above their surroundings. They are most numerous between Filyia and Kaltungo where they dominate the hills formed on Bima Sandstone.

The Biu Plateau and Biu Plains are formed over the most extensive series of lava flows. The Plateau consists of undulating plains between 600 -300 m (2 000 - 2 600 ft) above sea level formed over a series of overlapping horizontal lava flows. Within the Plains there are many low scarps and occasional larger escarpments which mark the end of individual flows. Boulder screes and mud flows are also associated with some flows. In the west, south and southeast the Plateau is bounded by a strongly dissected major escarpment rising through 150 - 300 m (500 -1 000 ft). The boundary in the northeast is less pronounced, and in many places is marked only by a low scarp 3-6 ra (10 - 20 ft) high. The Biu Plains, which extend northeast wards from this low scarp, consist of gently sloping basalt plains with a range of relief which seldom exceeds 3-6 m (10-20 ft). Rock outcrops are rare except where low scarps and boulders are associated with the limit of individual lava flows. Some minor variations in relief are associated with mud flows in between lava flows. The drainage lines are widely spaced and lie in broad shallow depressions.

The Longuda Plateau is also formed on a sequence of horizontal lava flows. The upland plains which make up the Plateau are far less extensive than on the 3iu Plateau and they are more dissected. Scarps and boulder screes are common and the Plateau is bounded by an escarpment on all sides. Less extensive lava flows occur at Garkida and Song. At Garkida lavas form a flat to gently sloping plain surrounding steep-sided volcanic cones, several of which contain well preserved central craters. The lavas blocked the Hawal river and are responsible for the abrupt change of form at this point. At Song the lavas flowed from similar steep-sided cones with well preserved craters. They followed existing valleys which were partially infilled by basalt, but have been subsequently exhumed, so that now basalt flows border many •of the streamlines and the underlying Basement rocks form the interfluves. The hills on the Biu Plateau between Meringa and Buratai are formed of pyroclastic rocks with locally developed lava flows. They are steep-sided volcanic cones and vents with summits as much as 180 m (600 ft) above the Plateau. Many show well developed craters and breached rims. One of the best known is Tilla where the crater contains a spectacular perennial lake.

Landforms Developed on Rocks of Group V: Chad Formation Consolidated sediments of the Chad Formation (rock type 11) are exposed, or lie near the sur face, south and west of Damaturu and southwest of Maiduguri. Elsewhere they are covered by unconsolidated superficial deposits (rock types 12-17) and it is with these more recent deposits that the landforms are closely associated.

South and west of Damaturu the northern boundary of the Gongola Valley is marked by a series of dissected plains rising to a marked break of slope with the Damaturu Plain. In some places this break forms a low escarpment. Below the escarpment the plains are undulating.

62 with finely eroded gentle slopes cut mainly in Chad sandstones descending to flat-bottomed valleys most of which are underlain by Cretaceous Pika Shales. Mesas formed from sandstones capped by ironpan stand above the plains. This dissected zone is the northward continuation of the stripped zone formed by the Gaanda Hills and the escarpment to the Biu Plateau. It marks the limit of erosion cycles now active in the Gongola Valley. Southwest of Damaturu the Anumma river changes abruptly from flowing northwest to flowing southwest. It seems probable that a previous tributary of the Damaturu river has been captured by headward erosion of the Anumma and that this change in direction marks the elbow of capture. The elbow of capture is associated with a nick point in the river profile and the upstream part of this valley probably owes its form more to erosion on the southern edge of the Chad Basin prior to the capture than to erosion governed by the Gongola base level.

Southwest of Maiduguri the southern part of the Damaturu Plain consists of very gently undulating plains with broad low interfluves and wide flat depressions. This topography is cut in Chad sediments partially overlain by drift, and many of the depressions are floored by Chad clays. Near Damaturu some of the interfluves are low mesas formed of sandstone capped by ironstone which is in turn overlain by drift (Klinkenberg, personal communication).

The plains which lie to the north of these gently undulating plains are relatively feature less and consist of hummocky plains with only minor undulations. The maximum height differ ence between crest and hollow does not exceed 1. 5 m (5 ft). There are no dunes although some of the depressions have a northeasterly linear orientation parallel to that of the dunes in the Lantewa Dunefield to the north. In some areas the hummocks have a similar orientation. Some parts of the Damaturu Plain show a ripple pattern of very gentle undula tions with low crests 200-300 m (660- 1 000 ft) apart. In general these undulations run north and south, but the pattern is distorted in the largely drift-filled valleys where the ridges tend to run down the valley slopes across the contours. The pattern of these undula tions is emphasised by lines of woody vegetation concentrated in the depressions and it is easier to recognise this linear vegetation pattern on aerial photographs than to recognise the undulations on the ground where the maximum range in relief is of the order of lm(3 ft). Grove (1958) attributes these undulations to relic dunes. A similar interpretation has been given to comparable patterns in Sokoto by Clayton (1966) and PAO (1969). They relate the vegetation differences to a contrast in the soil moisture status between the ripple and the interripple areas.

Dunes are the most prominent and widespread landforms associated with the aeolian sands of rock type 12. In the central and western parts of the area the dunes are of the sief type and form a regular pattern of long parallel sand ridges. These longitudinal dunes predomi nate in the Lantewa Dunefield and extend northwards into the Yobe River Complex. They are constantly orientated east-north-east. Over most of the Dunefield the dunes form a regular pattern of parallel ridges between 0.75 km Ok. mi) and 1.25 km (% mi) apart. Some are as much as 16 - 24 km (10 - 15 mi) long although they are more commonly broken by small discontinuities. The dune crests are generally between 3 and 9 m (10-30 ft) above the interdune depressions. The dunes are best developed in the north of the Dunefield where in some places they are as high as 11 m (36 ft). Along the southern border they are less frequent, shorter and generally not more than 3m (10 ft) high. In the Yobe River Complex the interdune areas are part of the alluvial plain; the dunes rise abruptly 6-9 m (20-30 ft) above the plain. Further north less well developed dunes of the same sief type and orientation occur in the Manga Plains-

There are similar northeast-orientated longitudinal dunes east of Bama. The interdune areas are covered by later lagoonal and deltaic deposits. Similarly orientated but less well developed dunes occur on the southeastern edge of the sand plains between Maiduguri and Mongonu. These dunes are also separated by later alluvial deposits. Northeast of these longitudinal dunes aeolian sands form islands which stand as much as 7 m (23 ft) above the surrounding flat clay plains. Pullan (1964; 1969) has shown that the lagoonal clays (rock type 15) were deposited over an undulating sand surface; in the south the highest remnants of this partially buried surface are the longitudinal dunes; further north the orientation of the dunes is lost and the sand plain emerges as the scattered sand islands. Together these dunes and islands represent the most easterly extension of the Lantewa Dunefield.

Aeolian and fluviatile sands of rock type 12 also predominate north of the Maiduguri to Mongonu road and dunes are again the dominant landform in an otherwise featureless sand plain. The area has been described by Pullan (1964). The most extensive group of dunes is orien tated north-north-west to south-south-east, that is transverse to the orientation of the longitudinal dunes. They form ridges up to 2.4 km (1& mi) long and roughly 3. 2 km (2 mi)

63 apart. They have an asymmetrical cross section and are steeper on the east-facing slope. The dunes are highest north and east of Gudumbali where they reach a maximum elevation of 15 m (50 ft). Further west they are much lower but the alignment can still be seen. In the northeast the dunes are separated by clay flats; elsewhere the interdune areas consist mainly of hummocky windblown sands.

The Lantewa Dunefield and the Damaturu Plain are separated from the Gudumbali Dunefield and the Bama Deltaic Complex by a complex ridge of beach sands (rock type 13), which can be traced from the Niger frontier east of Geidam, southeast through Maiduguri and Bama, to the Cameroon frontier. The continuation of this sand ridge into the Niger Republic has been mapped by Bocquier and Gavaud (1964) and into Cameroon by Pias and Guichard (1957). Its full extent has been summarised by Gavaud (1969). In Nigeria the ridge - known as the Bama Ridge - attains its maximum development between Maiduguri and Bama where it stands 12 m (40 ft) above the surrounding plains. It has been interpreted (Grove and Pullan, 1963) as an ancient barrier beach, or in some sections as a near-parallel series of such beaches or offshore bars formed when Lake Chad stood 53 m (174 ft) above its present level. The full extent of this larger lake has been summarised by Grove and Warren (1968). The largely dune-free sand plain which lies immediately to the east of the Bama Ridge and descends gradually from it is the beach of the former lake.

Grove and Pullan (1963) and Pullan (1964) recognise a similar but smaller beach ridge running west from Gambaru on the Cameroon frontier towards Mongonu. North of Mongonu the belt of lacustrine sands bordering Lake Chad (rock type 16) forms a series of parallel beach ridges which continue as far north as Arege. This second, more recent, series of beach ridges has been mapped in Niger by Bocquier and Gavaud (1964).

The deltaic deposits of rock type 14 which underlie the Bama Deltaic Complex form extensive sand and clay plains with little variation in relief. The pattern of landforms within these plains is very complex and is better appreciated from aerial photographs than on the ground. It consists of levees, meander channels and spill plains associated with several previous courses of the rivers together with similar landforms which are developing at the present time. Recent fans are developed at Maiduguri and Bama where streams break through the Bama Ridge. The central part of the Complex, between Maiduguriand Bama, consist largely of older deltaic landforms which have been considerably degraded by wind action and are partially masked by windblown sand. Near the Maiduguri to Mongonu road the transverse and longitudinal dunes of the Gudumbali Dunefield pass gradually into the deltaic sand and clay plains. The area consists of large interlocked clay plains with scattered sand islands. Many of the clay plains and the sand islands have the same northeast alignment as the longitudinal dunes. The complex pattern of deltaic landforms is further complicated by locally developed barchan dunes and by the longitudinal dunes and sand islands which emerge from beneath the cover of deltaic deposits and have become partially combined with them by subsequent wind action (Pullan, 19R4).

The lagoonal clays of rock type 15 are known locally as 'firki'. They form extensive flat clay plains above which the sand islands stand as high as 7 m (23 ft). In detail the plains consist of clays deposited in a series of shallow basins which have coalesced and have con necting or centripetal drainage. The basins are flooded annually, both by rain water and by water from the major rivers, and in some places clay is being deposited at the present time by these flood waters.

The sand plains and dunefields have been traversed in the past by several river systems, some of which do not now carry water, or carry far less water than they did in the past. The valleys containing these rivers have subsequently been partially filled by windblown sand and they are now to a large extent fossil.

The most extensive of these fossil river systems flows south from Niger, across the Manga Plains to join the Yobe River Complex near Gashua. Further east the complex pattern of largely drift-filled river courses and poorly developed dunes is further complicated by a series of steep-sided closed depressions; some are connected by the fossil drainage system, others are isolated. They are as much as 15 m (50 ft) deep; the larger ones lie below the level of the fossil river system and contain standing water. They occur over a wider area in Niger; only a small portion of their total extent lies within Nigeria. The Lantewa Dunefield and the Damaturu Plains are crossed by several river courses which have previously had wider valleys and a greater extent; the valleys are now partially drift-filled and largely fossil.

64 Ancient alluvial deposits of rock type 17 are most extensive in the Yobe River Complex and south of Bama in the Bama Deltaic Complex. The landforms associated with these deposits include ancient levees and point bars, spill plains, backswamps and meanders. Many of these landforms have subsequently been degraded by wind action and are now partially masked by windblown sand. Several stages of river deposition are contained in the Yobe River Complex, ranging from the present floodplain (see Group VI below) to the oldest alluvial deposits which covered the interdune areas of the longitudinal dunefield and are probably associated with the Hadejia river when it flowed into the more extensive Lake Chad near Gashua (Grove and Pullan, 1963). Some of these older deposits probably have a deltaic origin, but no dis tinction between deltaic and riverine landforms has been made. South of Bama ancient allu vial deposits form extensive terraces which border the present floodplain. Similar landforms border parts of the present floodplain of the El Beid river on the Cameroon frontier.

Ancient alluvium and its associated landforms are far less widespread in the Benue and Gongola river systems. Old meanders, levees and point bars mark previous courses of the Tiel river on the Cameroon frontier and bound the present floodplain of the Loko further west. Near Snellen terraces, old spill plains and levees border the present floodplains of tributaries to the Gongola; clay plains formed over ancient backswamps of the Benue occur near Karim Lamido.

Landforms Developed on Rock Types of Group VI: Recent Alluvium Recent river alluvium occurs along most of the water courses in northeast Nigeria. It varies in extent from thin discontinuous sands in the smallest streams to thick broad sands and clays on the major rivers. The sands form levees and point bars. Levees predominate in the smaller, generally fast-flowing streams; the broader, slowly flowing rivers have a complex pattern of both levees and point bars. Within this pattern clays are associated with back swamps and abandoned meanders.

Pediments and Colluvial Fans Pediments are formed over both the Basement Complex and Cretaceous sandstones in northeast Nigeria and it is convenient to describe them separately in association with the colluvial deposits which mantle them.

The two most extensive pediments are those bordering the Mandara Mountains and the Gaanda Hills, the latter pediment continuing north, west of the escarpment to the Biu Plateau. The western border of the Mandara Mountains is marked by a pediment which descends gradually westward to the Uba Plains from the sharp break of slope with the mountain mass. In the north the pediment continues round the main mass of the mountains east of Gwoza into the Cameroon Republic. The Pediment on this eastern side of the mountains is covered by up to 10 m (33 ft) of gravels and the underlying solid rock is not exposed (Pullan, 1969). The gravels have been deposited by streams from the mountains and by distributaries of the Ngoshi river, which has occupied various courses during its development. These gravel deposits have been strongly eroded and are now cut by many deep gullies. North and west of the Mandaras the pediment descends gradually towards the Bama Deltaic Complex. On its upper slopes it is overlain by gravel fans formed from outwash fans of both past and present streams draining the mountains; further downslope the gravels give way to finer deposits and clays characterise the lower slopes. The gravels of the upper slopes are eroded by many gullies; in some places the mid-slopes show gravel over the finer deposits which suggests that the upper pediment deposits have been eroded and redeposited (Pullan, 1969). South of Magadali the pediments between the Manadara Mountains and the Uba Plains are generally narrow and occur in deep valleys within the main mountain mass. Many of the pediment slopes have been covered by gravel fans which now form deep pedisediments and are in places strongly eroded into a fine network of gullies.

The southern edge of the Gaanda Hills is marked by a sharp concave break of slope with the pediment which descends gradually to gently undulating plains. The break of slope coincides with the boundary between Basement Complex rocks of Group I and Cretaceous rocks of Group II. This pediment is primarily an area of sediment removal and is largely free from colluvial deposits. It is floored by a thin cover of Bima Sandstone over the Basement, and as erosion continues the original surface on which the Sandstone was deposited is being exhumed. Further north in the Gongola and Hawal valleys the same pediment bevels Basement rocks as far as Garkida; it continues north of the Hawal, but occupies only a small area within the lower slopes of the Biu escarpment. Again most of this area is one of sediment removal and collu vial deposits are rare.

65 Pediments are formed on Basement Complex rocks around most of the inselbergs. Where the inselbergs are scattered the pediment forms only a small peripheral apron with only locally developed fans. At Hong and other places where the inselbergs occur in groups, the indivi dual pediments coalesce to form extensive plains sloping away from the inselbergs and the streams draining them form extensive fan deposits. The other main pediment in the project area is developed over Bima Sandstone on either side of the Lamurde hills bordering the Benue Valley. Colluvial deposits derived from the hills are widespread over the pediment and gravel fans are common.

Colluvial fans are a common feature of the eastern border of the Kerri Kerri Plateau, where the easily eroded Kerri Kerri Sandstone has been washed down and over the lower slopes formed on older Cretaceous rocks. The fans are not, however, deposited over a rock pediment formed on these rocks..

Geomorphological History Falconer (1911) attempted to elucidate the major crustal movements and drainage changes which have affected Nigeria. Many of his ideas have been followed by later workers, although this seems not always to have been acknowledged. Pugh and King (1952) outlined the geomorphological history of Nigeria, as a whole, but in the last 20 years most geomorpho logical investigations have tended to concentrate on certain problem areas: the high sur faces of the Mandara Mountains and the Jos Plateau, the plains adjacent to the Plateau, the evolution of the Benue Valley, or on the Pleistocene evolution of the Chad Basin. This land resources investigation of North East Nigeria has required a certain amount of geomorpholo gical correlation between these different areas. It has considered some areas not previously investigated, but in many respects this has served only to demonstrate that, with the present state of knowledge, only a very generalised geomorphological history of the North East project area can be attempted here.

Most workers regard the present landscape of Northern Nigeria as an arrangement of planation surfaces at different levels separated by escarpments or broad dissected zones. There is considerable range of opinion however about the nature, origin and evolution of these sur faces. The main sequence of events since the Jurassic was suggested by Pugh and King (1952). Their framework has been generally adopted, even if there is not general agreement that pediplanation is the process involved in the formation of the planation surfaces which they identified. Pugh and King (1952) consider that the whole of Nigeria was reduced to a vast pediplain at the end of the Jurassic, and that this plain formed part of the continent of Gondwanaland. Pugh (1954) interpreted the remnant higher erosion levels in the Mandara Mountains as relics of this Gondwana surface. Later Pugh (1955) and King (1962) suggested that, although the highest level could be remnants of the Gondwana surface, the more exten sive intermediate levels in this area were remnants of a later erosion cycle.

It is generally accepted that the continent of Gondwanaland began to break from the south and affected West Africa in the late Jurassic and early Cretaceous (Smith and Hallam, 1970). During the break-up the areas now represented by the Niger and Benue Valleys in Nigeria were the focus of major fracture lines separating South America from Africa. The Benue/Gongola trough was formed at this time as a northeast-trending tensional graben (Wright, 1968). North of the Benue the stable Basement areas which bordered this trough now form the Bauchi Plains (extending beneath the Kerri Kerri Plateau) and the Gaanda Hills (extending beneath the Biu basalts). The floor of the trough subsided intermittently during the Upper Cretaceous and well over 3 000 m (10 000 ft) of sediments were deposited in it. It seems probable that the stable masses on either side of the graben were subjected to intermittent region uplift to compensate for this subsidence. The sediments buried the main rift faults and overlapped onto the downwarped margins of the trough (Cratchley and Jones, 1965). The sedimentary material was derived from erosion of the uplifted Gondwana Basement surface, with the consequent creation of a second extensive planation surface on the Basement rocks. This surface probably continued across the Cretaceous sediments in the Benue/Gongola trough as a depositional surface.

At the end of the Cretaceous the sediments in the Benue/Gongola trough were subjected to compressional folding, as a result of the release of the tensional stresses which formed the graben structure (Wright, 1968). These earth movements were probably accompanied by uplift along an axis extending from Katsina, through Jos southeast towards Mambilla (Grove, 1957). The net effect of this deformation and uplift of the post-Gondwana surface was to create a

66 major upland watershed area along this axis and downwarped areas to the northeast. By the Miocene the post-Gondwana surface had been considerably eroded, the resulting African surface was developed on both Basement and Cretaceous rocks and the continental Kerri Kerri Sandstone had been deposited in basins within the downwarped area. Pew fossils have been found in the Kerri Kerri Sandstone and its age is uncertain. Carter et al. (1963) and Reyment (1965) suggest Palaeocene, although they allow that it may be younger. Haughton (1963) tentatively assigns it to the Eocene. Sandstone accumulation had therefore probably ceased in these basins by the latter part of the Eocene and rivers started to flow northeast across the newly formed depositional and denudational African surface. It seems most likely that the Jamaare, Komadugu Gana and Yedseram, and the present-day upper reaches of the Gongola and the Hawal were initiated at this time. Over the same period in the southwest the lower reaches of the Benue (the proto-Benue) had cut headwards in the less resistant Cretaceous sediments providing a much lower base level for planation (Grove, 1957).

King (1962) suggests that further uplift occurred in the Pliocene and initiated another cycle of erosion. This post-African cycle is represented by the Uba Plains and by the Bauchi Plains to the west of the project area. Further north this post-African planation surface is downwarped below the Chad Formation.

During the Pliocene extensive sheets of ironpan (laterite) developed over the post-African planation surface (du Preez, 1956). These are preserved on the Basement plains north and west of Mubi, under a thin cover of drift on Kerri Kerri Sandstone of the Potiskum Plain and in the Kadi Escarpment (Dowling, 1963) and on the Gombe Sandstone at Fika; elsewhere in the more dissected areas only remnants of primary ironpan are preserved. Pullan (1968) has des cribed the types of primary ironpan which occur and the range of secondary ironpan deposits which have been subsequently derived from them. More than one phase of ironpan formation has been recognised, but the age relations are not fully understood. South of Damaturu, Klinkenberg (personal communication) has mapped ironpan overlain by Chad sediments; further west, Hope (personal communication) has mapped mesas of Chad sandstones preserved by a capping of ironpan.

Probable movement of the West African monocline (King, 1962) at the end of the Pliocene involved more uplift and warping. Further cycles of erosion, related to changes in oceanic base level, progressed up the Benue trough and resulted in a considerable enlargement of its catchment (Grove, 1956). During this enlargement tributaries extended northwards to capture the Gongola and the Hawal. The boundary between the planation surfaces related to the post- African erosion cycle with an inland base level, and surfaces related to later cycles con trolled by the present oceanic base level of the Gongola and Benue,is marked by a stripped zone which extends from the southern edge of the Mandara Mountains, through the Gaanda Hills and the western escarpment of the Biu Plateau and west to the Kadi Escarpment and the western edge of the Kerri Kerri Plateau. This stripped zone continues further west, beyond the North East project area, between the Kerri Kerri Plateau and the Bauchi Plains.

In the Benue Valley, west and south of the North East project area, Grove (1956) has recog nised a planation surface between 450 -580 m (1 500 - 1 900 ft) related to oceanic base level. It seems likely that the plains in the Gongola Valley around Kaltungo and to the west of the Biu Plateau were formed by the same erosion cycle. Grove has shown that the subsequent cycle had several phases and has recognised lower surfaces at 180 and 100 m (600 and 330 ft). Both of these lie west of the North East project area and, although erosion has continued in the Gongola Valley throughout this cycle to the present day, no surfaces related to these two phases have been recognised.

The region now occupied by the Chad Basin has been a depositional region almost continuously since the continental sandstones of the Kerri Kerri Formation were deposited in downwarped basin areas of the post-Gondwana surface. After deposition of these sandstones and the establishment of the northeast-orientated drainage across the post-African planation surface, downwarping continued and the sediments of the Chad Formation were deposited. The total amount of downwarping is indicated by the depth to pre-Chad rocks; at Goniri (south of Damaturu) the base of the Chad Formation is 89 m (290 ft) below ground level, at Maiduguri 580 m (1 900 ft) and on the shore of Lake Chad north of Mongonu 760 m (2 500 ft).

There has been considerable climatic fluctuation since the Pleistocene. These climatic fluctuations are reflected in the sequence of superficial deposits overlying the rocks of the Chad Formation, and the landforms associated with them. Pullan (1964) has suggested a tenta tive chronology for these fluctuations in Nigeria, and the following paragraphs are largely a summary of his observations.

67 The characteristics of the sands forming the extensive plains west of the Bama Ridge suggest that they were of fluvial origin - derived mainly from Basement rocks to the south and west. Their aeolian character and the longitudinal dunefields were formed subsequently during an arid phase when desert conditions extended as far south as 11° 30' N. The Bama Ridge trun cates these longitudinal dunes and is younger than them. The shoreline of Lake Chad at this stage was 333 m (1 095 ft) above sea level and extended west from Magumeri as far as Gashua (Grove and Pullan, 1963). The extensive clay flats which now lie within the Yobe River Complex in the vicinity of Geidam were probably deposited in lagoons behind the beach ridge. At this period the Yobe river system included many south-flowing tributaries from the Niger Republic and northeast-flowing tributaries from the Potiskum and Damaturu Plains. These are now largely fossil and do not reach the main river system. The change in direction of the Yobe river at Damasak, from an easterly to a northeasterly direction, and the presence of a large quantity of sand to the south suggests that the Yobe built a large delta of coarse sand into Lake Chad east of the beach ridge. The large lake with which the beach ridge and this delta were associated flooded parts of the longitudinal dunefield. Deltas were also formed by the Yedseram and the Alo rivers until they reached the beach ridge. The way in which both these rivers have been deflected from their course by the beach ridge suggests that it existed before the river deltas reached it and that the rivers finally broke through gaps in the ridge.

Por the delta sands deposited in the area now occupied by the Gudumbali Dunefield to have been formed into dunes, a regression of the lake from the line of the Bama Ridge must have followed. Pullan suggests that the dunes in this dunefield were formed along an open shoreline as the lake gradually retreated to its present position. Further south the dunes were confined by clay flats formed by the extended deltas of the Yedseram and the Alo. The extent of the regression of the lake at this period is not known but it was probably of short duration. A further transgression, rather than a period of stillstand, is suggested by the clays and silty clays in the interdune areas in the eastern half of the Gudumbali Dunefield. During this transgression the lake also flooded part of the longitudinal dunes east of Bama.

This postulated increase in the lake size is associated with a further series of river deltas. The course of the Yobe was blocked by the transverse dunes and formed a delta further north, largely to the north of its present course. The large fossil delta to the north of the present Yedseram delta was probably built during this transgression. There is also some evidence that the Alo may have been a tributary of the Yedseram at this stage, because south west of the Bama Ridge they are separated by only a few miles of low-lying ground and there is no old delta of the Alo comparable in size to that of the Yedseram. Further east the El Beid was part of the Chari river delta. This delta extended far into the lake and from it the Ngelewa sand ridge formed as a spit or an offshore bar. The lagoonal deposits of the Yedseram and the El Beid deltas, which now form the 'firki' clay flats, were confined northwards by this Ngelewa ridge.

A gradual reduction in the area of the lake followed this last transgression and was accom panied by the building of small deltas by the Alo and Yedseram. These rivers are now extend ing their deltas into seasonal shallow lakes impounded by the Ngelewa ridge and the lacus trine sands bordering the present lake. Records of the lake level and river discharges are not adequate to tell whether the lake is retreating further from its present shoreline.

68 PLATE 1/5 The road to Dikwa across the 'firki' (black cracking clay plains). A 'sand island' lies along the skyline.

PLATE 1/6 The Bama Ridge just west of Maiduguri. Looking eastward along the southern face with the de flected Ngadda river flowing towards the camera.

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70 HYDROLOGY

M G Bawden

SURFACE WATER The North East project area includes parts of two major drainage basins: the internal basin of Lake Chad and the Benue river basin which flows to the Niger and then to the Atlantic Ocean. Text Map 11 shows the main catchment areas in the project area. The area of each of these catchments within the detailed boundary of the project is shown in Table 2. Table 3 shows the mean monthly and mean annual discharge for each of the rivers for which sufficient data are available.

TABLE 2 Area of river system catchments inside project boundary

Area River system km2 mi2

Lake Chad Basin total area (2 335 000) (900 000)

*Yobe river system 21 200 8 200 Damaturu river system 4 200 1 600 Kyauwo river system 3 500 1 300 Yedseram river system 14 600 5 700 *E1 Beid river system 4 400 1 700 areas with only local surface flows 58 400 22 500

Total 106 300 41 000

Benue River Basin total area (337 000) (130 000)

»Gongola river and undifferentiated tributaries 24 300 9 400 Hawal river system 11 900 4 600 Anumma river system 5 100 2 000 •Benue river and undifferentiated tributaries 7 700 3 000 *Tiel river system 1 300 500 Kilunga river system 5 700 2 200 *Pai river system 13 700 5 300

Total 69 700 27 000

* River systems which extend beyond the detailed boundary of the North East Project TABLE 3 Mean monthly and mean annual discharge of selected rivers

Mean monthly discharge in m3/s for eight stations Mean monthly stage cm

River Benue Gongola Yobe Ngadda Yedseram El Beid

Station Yola Numan Lau Bare Damasak Gashagar Yau Maiduguri Bama Gambaru

Period of 1955-1958 1955-1957 1959-1964 record 1955-1957 1963-1965 1955-1960 1957-1962

January 100 NA 190 NA 28 25 23 0 0 323

February 30 NA 110 NA 6 7 11 0 0 169

March 23 NA 67 NA < 1 2 2 0 0 59

April 16 NA 45 > 1 0 0.4 5 0 0 16

May 45 56 121 52 0 0 > 1 0 0 4

June 327 395 415 127 > 1 0 0 0 0 4

July 879 953 1 188 239 9 6 4 1 0.92 20

August 2 150 2 400 2 915 683 30 22 17 22 64 153

September 3 583 4 500 4 678 972 42 34 23 47 140 145

October 3 033 3 200 3 615 565 47 35 25 36 76 164

November 597 637 685 NA 55 37 27 14 22 280

December 220 150 402 NA 58 40 29 4 0 395

Mean annual discharge 730 NA 1 081 NA 25 17 14 10 12 m3/s 72 m3/s

TABLE 3A Mean monthly and mean annual discharge of selected rivers

Mean monthly discharge in ft3/s(cusecs) for eight stations Mean monthly stage ft

River Benue Gongola Yobe Ngadda Yedseram El Beid Station Yola Numan Lau Bare Damasak (jrashaga r Yau Maiduguri Bama Gambaru 1955-1958 Period of 1955-1957 1955-1957 1959-1964 1955-1960 1957-1962 record 1963-1965

January 3 530 NA 6 707 NA 985 884 820 0 0 10.61

February 1 059 NA 3 883 NA 222 239 382 0 0 5.54

March 812 NA 2 365 NA 42 53 72 0 0 1.95

April 565 NA 1 589 10 0 14 166 0 0 0.52

May 159 1 977 4 271 1 818 0 0 3 0 0 0.12

June 11 543 13 944 14 650 4 483 0.8 0 0 0 0 0.13

July 31 029 33 641 41 936 8 437 328 206 124 45 0.03 0.67

August 75 895 84 720 102 900 2 411 1 070 789 612 766 2.10 5.03

September 126 480 158 850 165 133 34 312 1 493 1 184 808 1 646 4.58 4.75

October 107 065 112 960 127 610 19 945 1 660 1 223 893 1 274 2.50 5.39

November 21 074 22 486 24 181 NA 1 938 1 313 960 485 0.72 9.18

December 7 766 5 295 14 191 NA 2 057 1 398 1 032 152 0 12.95

Mean annual 417 2544 discharge 25 800 NA 38 200 NA 815 601 497 363 cusecs cusecs 72 GROUNDWATER AREAS TEXT MAP 10 10° 12° 14° 14° 1 l \ \ + 1 V\ '"* ^— + C\/^ \ + ) SCALE 1:3 ,000,000 *7A * / MILES 0 25 50 75 loo MILES ,'/::::) \ I 1 • i */••"•'( * ^ \ * + *if^''''v\ « T V fc * ^l/N^SC-. •••-••• VA » -ƒ- VV\A! VSO" «V^Ï::xVxxxxxJ& \ <° V ^xx:xx::x:X'|x£\ *« O *- + + + + + + + + + + + •*- + * ==^^?Äi ? Xxxxx^s :•:•:•:•:•: | '>r *•». is ! :-:-:-:-:V % -7 „"ÏOM/tsena ^M:;:;x;;;x;:;;:x;x;:;bï;x;i;:; 5 -=5^^:x:::::;:x:x:::x:x::ï::x%::;X;Xo j^»^ ; v_x A™fcx-x-X'X'X/ïi«ï'X%rvX'««^-;5!K-'"-i i * Nguru Gashua { 5 ^ = 5?«Hiiii^^^Ä \ w/7^ JS^ j/Js /// wllflllllfe • f~^ y%y /u ^xfiadejia ** ^/^ C ill ^^'W^^m^y^^^^^^^^y^^^^ 6

•xv?V*- Siï 4$ Xîiiii lllllllK 2° 12° ;-i/J+ ~^t}( $< \ ^ Iplltl \ °pi|;::I™ ÎI^SCUGURIÎ»^ ^^^^liiiiiÉii^Pil^la^î^ 5 /(«MWSShl.-...-. • JÄL--J-I:»:S # ^ -~^Sl5:SSSfi?*'-j"•-V* " nMfskurA _^0^VijSL*1 Dimaturu •- 1 ..^LAzare _^S/~^^ / 1 11 'É^ffl^jwfe^li \PH \ 3 \\ ^._—?%p« wmmfoA /(Xy^ 1 „•* 2b i/^^DjWn 1 xrecharge \^\ • II1 O //*. \( X». / " I.A. **s -6 ^-rr^ / N, ODambyoa ( A \S^/ \J\¥ ** • WaTapa^ x >^ fc_—/*\ /• "*• — -J ƒ \ \\ f * \ /^~\^^ \ J F \1 /^ ** l//*\.l */^v f "* S 4 X x^ J] v/1 ƒ + y/\w 3 \ ^"/ -Ny \ y * 2Jty '^^^"•^ / éït\^ * ^^St. /Il x. * way\ /(vvx^ • 1 Gambe T Cza\ ] ^^/ MuPS' / 2a yf* \ / '"inmbm ^"^^ * A/ / -10 10° 2b, V Ai + ^^PSOAE t ^** /\ j V -f- Kayunoéo|V Wt 2 b- 2a) .,..*'* A fi§\/ 2a 4/ OMIT

Yo ^x^^^ C3^2b Groundwater Areas ' 5 Chad sediments Availability of water from middle zone 1 Igneous and metamorphic rocks aquifer:- /PJ 2a Cretaceous sandstones •'.''.• High-yield artesian aquifer . . Moderate-yield artesian (bl) 2b Cretaceous shales g, sub-artesian aquifer (b2)

3 Kerri Kerri sandstone Low-yield artesian aquifer

\J Main Road A Basaltic rocks Low-yield sub-artesian aquifer / Railway _ . . H 1 1- * 5 Chad sediments ^^ «=» Hydrochemical front International Boundary +++++++ 6 Recent alluvium ,>* ^^ Direction of flow

1 Q° 1 1 R 10° 12° East of Greenwich Derived from information in Barber (1956) and Miller et al (1968) D.O.S. (LR) 3064 V Drawn and photographed by Directorate of Overseas Surveys 1971 Printed by Ordnance Survey Copyright reserved 7/ 7(/5326/OS CATCHMENT AREAS TEXT MAP II 10° 12' l4'IT-

SCALE 1:3,000,000 MILES 0 25 50 75 i—L_

12°

fa/ •—•>

LEGEND HowaV.

Gombe LAKE CHAD DRAINAGE BASIN A Yobe river system B Damaturu river system 10° / '1 C Kyauwo river system K D Yedseram river system >Song E El Beid river system ngolj). \ 'W BENUE RIVER DRAINAGE BASIN F Gongola and undifferentiated ,\ tributaries ONu Mv Hawal river system / Anumma river system Benue and undifferentiated tributaries Tiel river system Kilunga river system Pai river system M Wase river system

Lake Chad - Benue Divide

_ . _• . — . —. Gongola watershed Main Road Other watersheds Railway V\\\\\\^ Areas with only local surface flow

*• + + + + + + _ International Boundary <*- » Flood liable to flow in either direction J_ 10° 12° East of Greenwich D.O.S.(L.R.)3064T Drawn and photographed by Directorate of Overseas Surveys, 1969. Copyright reserved Printed by Ordnance Survey. LAKE CHAD DRAINAGE BASIN The Lake Chad drainage basin is an internal drainage basin with a total area of 2 335 000 km2 (900 000 mi2) (Gischler, 1967). It extends from the Hoggar and Tibesti mountains on the northern frontier of the Niger Republic to the Chad/Sudan frontier in the east and the high lands of the Chad/Congo divide in the south. In Nigeria the watershed of the Chad Basin runs from the Niger frontier north of Kano, south to the Jos Plateau (see Text Map 1) and then northeast to Potiskum and Damaturu before swinging southeast to Mubi and the Cameroon frontier. 1 660 000 km2 (64 000 mi2) of the Chad Basin lie within Nigeria, of which 106 300 km2 (41 000 mi2) are covered by the North East project.

Ninety-five per cent of the water which flows into Lake Chad comes from the Chari and Logone river systems, which rise in the highlands in southern Chad and the Central African Republic and flow into Lake Chad from the southeast. The El Beid and Yedseram river systems rise in the Mandara Mountains and together supply about 4 per cent of the water to Lake Chad. The Yobe river system, whose upper reaches drain the Jos Plateau and the plains to the north of it, supplies less than 1 per cent of the total. Thus less than 5 per cent of the total inflow to Lake Chad originates in Nigeria.

The major tributaries of the Yobe river system are the Jamaare which rises on the Jos Plateau and the Kano (subsequently the Hadejia) which rises in the highlands to the north of the Plateau and flows northwest as far as Kano before swinging northeast towards Lake Chad. The third tributary, the Komadugu Gana, rises further east on the Bauchi Plains. Records have been made at several stations on the Yobe river system (N. Nigeria Govt., 1963 and 1965) and its behaviour has been summarised in a report on the Lake Chad Basin within Nigeria prepared by the United States Department of the Interior (USAID, 1968). Virtually all the water is derived from seasonal rainfall on the Jos Plateau and the Basement plains west of the North East project area. In the project area itself there is very little surface flow, rainfall is largely balanced by evaporation and the Yobe river system as a whole is a losing one. The estimated total average annual runoff from the headwater tributaries is 6 167 x108m3 (5 000 000 acre ft) and probably not more than 1 850 x lOema (1 500 000 acre ft) flows past Gashua. The additional inflow to the Yobe from the Komadugu Gana is about 986.8 x 10em3 (800 000 acre ft per annum). At Damasak, 10 km (6 mi) below the confluence, the combined average annual yield is only about 986.8 x lOems (800 000 acre ft) and of this only about 444 x 10em3 (360 000 acre ft) reach Lake Chad. Most of the loss is due to evapora tion, although there is some recharge of aquifers in the Chad Formation (see section on hydrogeology).

The pattern of flow in the Yobe river system is closely related to the rainfall pattern in the highlands. The peak river stages in the Jos Plateau and on the Basement plains are in late August. As the streams flow northeastwards they flood the extensive old stream channels and depressions in the Yobe River Complex (see Text Map 2). Large areas are inundated west of Gashua, at the confluence of the Hadejia and the Jamaare, and in the vicinity of Geidam at the confluence with the Komadugu Gana. This widespread flooding retards the travel of the peak flow downstream. The peak flood reaches Hadejia in September, Gashua by mid-October, Geidam by November and Damasak by December. It does not reach Lake Chad until January. The average peak flow at Hadejia is about 1 981 mas (70 000 cusecs). This decreases to about 283 mas (10 000 cusecs) at Gashua, to 65 m3s (2 300 cusecs) at Damasak and 40 m3s (1 400 cusecs) at Yau (Yo) 20 km (12 mi) from the shores of Lake Chad.

The flow decreases rapidly after the flood peak passes. Usually the flow is zero in the lower reaches of the river from April through to June. In years of high runoff a small flow of 0.28 -0.57 m3s (10 - 20 cusecs) may occur east of Gashua throughout the dry season.. Swamps and pools remain even in years of low runoff. The limited local runoff into the main river system does not materially affect the flooding as it is dissipated before the arrival of the flood peaks from the highlands further west.

The main components of the Yedseram river system are the Yedseram itself, which rises in the Mandara Mountains east of Mubi, and the Ngadda which rises further west on the upland south east of Damboa. North of Mubi many smaller tributaries of the Yedseram drain the western slopes of the Mandara range. The El Beid also rises in the Mandara range, but further east in the Cameroon Republic, and only a small part of its catchments lies in the project area. The Yedseram and El Beid river systems have a similar regime to the Yobe river system in that they depend on seasonal rainfall in the mountains and the upper reaches and that their lower reaches are regions of extensive flooding, high evaporation and net loss.

77 The Yedseram and the Ngadda flow north from the Mandara range and the upland west of the Yedseram plains. They are in separate channels as far as Bama and Maiduguri where they breach the Bama Ridge. Thereafter they have no continuous channel and their flow is diffused in the extensive swamps and depressions of the Bama Deltaic Complex. Only the Yedseram crosses the Chad Lagoonal Complex and reaches Lake Chad with a distinct but far smaller channel (the Mabuli). The Ngadda has no outlet to the Lake. The total average annual runoff in the headwaters of the Yedseram system is about 1 233.5 x l08m3 (1 000 000 acre ft) of which only about 123.4 x 10em3 (100 000 acre ft) reach Lake Chad (Raza, 1969).

The streams which originate in the Mandara Mountains have their peak flows in August; but the rivers do not usually start flowing in the Maiduguri/Bama region until early August. The Yedseram at Bama has an estimated annual yield of 308.4 x 106m3 (250 000 acre ft) between August and November, with a peak flow of 85 m3s (3 000 cusecs) in the middle of September. The river is usually dry by the end of November. The estimated annual yield of the Ngadda at Maiduguri is 246.7 x 10em3 (200 000 acre ft) with a peak flow of 57 m3s (2 000 cusecs). Its flow is also confined to August - mid November with no dry season flow. The flow of the Ngadda at Maiduguri is however more uniform than the Yedseram at Bama. This is because Lake Alo, south of the Bama Ridge, stores the early runoff from the upper reaches. The average annual inflow to Lake Alo is about 431.7 x 10em3 (350 000 acre ft) - 50 per cent more than the yield at Maiduguri.

Between the Komadugu Gana and the Yobe in the north and the Yedseram river system in the south there is very little runoff. Several areas are flooded following heavy rain but vir tually all the water is lost, mostly by evaporation. Water flows in the upper reaches of the Damaturu and the Kyauwo river systems immediately following the rains, but it does not flow beyond the line of the Bama Ridge and does not significantly affect the flow of the Ngadda at Maiduguri.

The hydrological regime of the El Beid river system is very complex, partly because flood- waters from the Logone and Chari rivers flow into it. The main tributary of the El Beid river system in Nigeria is the Nasawa (or Goma) which drains the northern flanks of the Mandara range and breaches the Bama Ridge east of Bama. The El Beid flows between mid-July and April with a mean annual yield of 1788.6 x10em3 ' (1 450 000 acre ft). There is a range 863.5 x 10em3 (700 000 acre ft) to 2 713.7 x 108m3 (2 200 000 acre ft) between low and high yield years (Raza, 1969). Hydrographs on the El Beid at Gambaru (on the road from Dikwa) indicate two peak flow periods; one in August related to rainfall in Nigeria and the Mandara Mountains in Cameroon and the second in December related to floodwater from the Logone and the Chari.

The level of Lake Chad is closely related to the hydrological regime of the Chari and the Logone which together contribute 95 per cent of the total inflow. Lake Chad is highest in December and January, after which the water level falls until July. On average the lake receives a total runoff of 41 075.6 x lOem3 (33 300 000 acre ft) and about 4 934 x 10em3 (4 000000 acre ft) of rainfall per annum. It owes its existence to the balance between this water input and evaporation. Infiltration losses are thought to be negligible. Mean annual evaporation from the lake surface is 2 290 mm (90 in) with the highest mean monthly value of 250 mm (10 in) in May. The maximum recorded lake level is 284 m (932 ft); the lowest is 281 m (922 ft). With these changes in level the flooded area varies from a maximum of 25 000 km2 (9 600 mi2) to a minimum of 15 000 km2 (5 800 mi2) (Raza, 1969).

BENUE DRAINAGE BASIN

The south of the project area is drained by tributaries of the Benue. The Benue itself rises further south and east in the highlands of central Cameroon. It flows from east to west along the southern border of the project area to join the Niger at Lokoja, west of Makurdi (see Text Map 1). The total area of the Benue drainage basin is 337 000 km2 (130 000 mi2) of which 233 000 km2 (90 000 mi2) are in Nigeria and 69 200 km2 (27 000 mi2) fall in the project area. The hydrology of the Benue river and its major tributaries has been investigated by NEDECO (1959). The regime is governed by high rainfall in the highlands in central Cameroon and in the Nigeria/Cameroon frontier region south of Yola; rivers entering the Benue from the north, from the North East project area, contribute less than 10 per cent of the total dis charge into the Niger.

78 In general throughout the North East project area the dissected and highland regions of the Benue drainage basin are characterised by high runoff and fast-flowing seasonal streams which feed larger slow-flowing rivers on the plains. These larger rivers contain water all the year round and have a weakly perennial flow.

The Gongola is the largest tributary to join the Benue from the north and it drains two- thirds of the Benue basin within the project area. It rises on the Jos Plateau and flows northeast across the Bauchi Plains before cutting through the Kerri Kerri Plateau and swing ing abruptly south at Nafada to flow through the Gongola Valley and join the Benue at Numan. 2 major tributaries of the Gongola rise on the Biu Plateau. The Anumma flows north from Buni and then turns abruptly southwest to join the Gongola at Nafada; the Hawal which is the larger of the 2, flows northeast from Biu and then swings south and southwest to join the Gongola north of Snellen. Minor tributaries flow direct to the Gongola from the northern half of the Kerri Kerri Plateau and within the Gongola Valley itself. Water flows in the Gongola and the Hawal throughout the year, but with a considerable seasonal variation in dis charge. During the dry season there is standing water or water can be obtained from the sand bed of the Anumma and from several of the smaller tributaries but flowing water is restricted to the period immediately following the rains. Most of the water in the Gongola originates on the highlands of the Jos Plateau; the average annual discharge into the Benue is 8017.8 x 106m3 (6.5 million acre ft) of which the Hawal contributes only 925 x 108m3 (750 000 acre ft); there are no records for the other tributaries. The Gongola reaches its maximum flow in September when the average annual discharge for 1955-7 was approximately 1670 m3s (59 000 cusecs) (NEDECO, 1959); during the period of minimum flow, from December to the end of May, discharge of the Gongola falls as low as 5.7 m3s (200 cusecs) and on the Hawal to as little as 0.28 m3s (10 cusecs) (Raza, 1969).

West of the Gongola Valley the southern part of the Kerri Kerri Plateau and the Benue Valley west of Kaltungo is drained by the Pai. To the east of the Gongola the Gaanda Hills and the southern margin of the Uba Plains are drained by the Kilunga and further east the Tiel drains the southern margin of the Mandara Mountains. As with the Gongola and its tributaries these rivers are seasonal. In the Benue Valley the main feature of the flow pattern of the Benue is the large area of the floodplain between Numan and Lau which is flooded annually. This flooding has the effect of both merging the twin peak flood at Numan to a single longer peak further downsteam, and of delaying the downsteam peak flood. At Yola the mean annual yield is 23 437 x 10em3 (19 million acre ft) with discharge maxima between 4245 and 5660 m3s (150 000 and 200 000 cusecs) in September and in October. At Lau the maxima are less distinct and a flow of between 4 245 and 5660 m3s (150 000 and 200 000 cusecs) is maintained from early September until late in October. At Augwan Taru (downstream from the confluence with the Pai) the mean annual yield is about 37 005 x 10em3 (30 million acre ft) with a maximum of more than 5660 m3s (200 000 cusecs) which lasts from mid-September until late in October.

GROUNDWATER

The distribution of groundwater in northern Nigeria has been described by du Preez and Barber (1965) and there are several reports presenting the results of investigations of the artesian aquifers within the Chad Formation.

Du Preez and Barber recognised 10 groundwater areas in northern Nigeria, 6 of which occur within the area covered by the present investigation. Each is closely related to 1 of the major groups of rocks described in the geology section. The hydrological characteristics of each of these groundwater areas are summarised below; their distribution is shown on Text Map 10.

Area 1 Igneous and Metamorphic Rocks, Mainly of the Basement Complex Over most of the area underlain by the Basement Complex there is a thin discontinuous mantle of weathered rock with sedentary soils, colluvial material or ironpan. The average thickness of this mantle is about 15 m (50 ft) but in some areas it extends to depths of 60 m (200 ft). The finer grained rocks are generally more resistant to weathering than the more coarsely grained types. Joints and fractures are common and vary greatly in their depth and lateral persistence. They form both tight cracks and open fissures and in some areas the rocks have been faulted with associated crush zones. The joints probably do not extend beyond 90 m (300 ft); larger fractures and fault zones go deeper. In general, joints are better developed in the granites and quartzites than in the gneisses, migmatites and schists.

79 Groundwater occurs in these igneous and metamorphic rocks either in the weathered mantle or in the joint and fracture systems in the unweathered rocks. The presence of groundwater therefore depends on whether the mantle is sufficiently thick and extensive to provide a reservoir, or whether joints and fractures are present in the fresh rock. Thick colluvial deposits provide good reservoirs, but apart from this the Basement Complex rocks generally form a poor source of groundwater. The decomposed mantle is usually too thin to harbour large quantities of water and is usually too clayey to be highly permeable. The joints are normally too poorly developed to compensate for the inadequacy of the weathered zone over lying them. The average depth to the watertable is 36 m (120 ft). Wells, if carefully sited, will normally provide an adequate supply for village communities. The average yield from wells in Basement rocks is 3 650 litres (800 gal) per hour.

Small springs and seepages are common in areas underlain by rocks of the Basement Complex. They give rise to small swamps and moist areas in many localities and in some places they coalesce to form streams. Throughout groundwater area l seepage springs are the main source of perennial surface water.

Area 2 Cretaceous Sedimentary Rocks The principal water-bearing Cretaceous strata are the sandstones of the Bima, Yolde and Gombe Formations. Where these strata outcrop groundwater normally occurs under watertable condi tions. Clay lenses which occur confined within the sandstones give rise to localised pressure water. The actual groundwater conditions differ in different areas because of the varying relations of these sandstones to the remaining, predominantly argillaceous strata. The permeability of the Bima Sandstone is generally low because of interstitial clay derived from decomposed feldspar; the Sandstone is however believed to contain large reserves of available groundwater. The rocks of the Yolde Formation vary considerably in lithology and texture and their water-bearing properties are gradational between those of an aquiclude and aquifer. High-yielding pressure aquifers have been proved at several horizons and con siderable sub-artesian rises have been recorded. 8 boreholes in the Gombe area have yielded from 8 200 to 18 200 litres (l 800-4 000 gal) per hour. The Gombe Sandstone contains both aquifers and aquicludes and contains pressure water confined by intra-formational shale horizons. Sub-artesian yields between 12 700-24 500 litres (2 800-5 400 gal) per hour have been obtained from the base of the Formation. The Gongila Sandstone also contains pressure water where it is overlain by the Fika Shales. Limited supplies of water are obtained from the Dukul and Jessu Formations, both of which contain porous and permeable horizons.

The other Cretaceous Formations do not generally form good aquifers and the limited ground water which they do contain is often highly mineralised. The impermeable clays and shales yield negligible amounts of water. The limestones do not usually form aquifers; the thin sandy lenses contain water, but yields are small. The hydrological importance of these sediments is that they confine water in the underlying Bima and Yolde Sandstones. Consider able quantities of groundwater also occur in the colluvial sands which surround the Lamurde anticline and are underlain by clays and shales (Klinkenberg, 1967).

Area 3 Kerri Kerri Sandstone Groundwater occurs mainly under watertable conditions in the Kerri Kerri Sandstone. The saturated portion of the Formation contains a large quantity of water but much of this is not readily exploitable because interstitial clay and silt reduces its permeability. However there are some good-quality aquifers. Occasional clay lenses give rise to perched aquifers in some localities. Confined water occurs in some places where the Kerri Kerri is overlain by impervious sediments of the Chad Formation north of the outcrop.

Dousse (1969) has mapped the watertable in the Kerri Kerri Formation. The depth varies widely ranging from 0-180 m (0-600 ft) below the surface. The slope of the watertable is closely related to the slope of the land surface, although the watertable contours are less steep. The irregularities in the steepness and direction of the slope of the watertable are caused by both vertical and lateral changes in the permeability of the rocks and by the thickness of the water-bearing strata. Groundwater ridges coincide with the major stream channels and the streams supply water to the permanent groundwater by influent seepage. The watertable beneath and adjacent to the streams is usually near the surface, but between the streams the depth to the watertable increases rapidly. The gradient ranges from 0.9-10.7 m per km (3-35 ft per mi) and averages approximately 3.7 m per km (12 ft per mi) (Dousse 1969). Gradients of 12.2-21.3 m per km (40-70 ft per mi) are common in the western part of the area; this is a reflection of the steep slope of the land surface and probably also reflects an increase in permeability of the water-bearing sediments.

80 In areas with a comparatively dense drainage pattern the watertable is usually within reach of hand-dug wells but the watertable is generally too deep where the drainage pattern is sparse; in such areas the groundwater can only be exploited by drilled wells. Over most of the Potiskum Plain and near the Gongola river the watertable can be reached by hand-dug wells which are seldom deeper than 90 m (300 ft). North of the railway the watertable lies about 150 m (500 ft) below the surface and hand-dug wells tap only perched aquifers. In some places in the southwest of the Kerri Kerri Plateau the watertable is deeper than 150 m (500 ft).

Some recharge occurs along the line of the Gongola river because of the permanent underflow that originates in the underlying Basement Complex rocks of the Bauchi Plains, to the west of the Kerri Kerri Plateau. Away from the Gongola virtually all the recharge is from rain. The maximum rise in the watertable occurs towards the end of July and early in August, during the heaviest rains, when rises of up to 10 m (33 ft) are common in shallow wells; deeper wells show comparable, but slower rises. The levels begin to fall soon after the end of the rainy season.

East of Potiskum the watertable intersects the ground surface. There have been remarkable rises in the watertable in this area in recent years and new springs, seepages and perennial streams and lakes have been formed. Water levels in wells have also risen substantially and rises of up to 50 m (160 ft) have been recorded. Carter and Barber (1958) suggested that this was a result of deforestation following increased settlement and cultivation. Later work by Dousse (1969) has confirmed this hypothesis and shown that the increased runoff due to deforestation, although important during the rainy season, is smaller than the increase in percolation to the watertable.

Area 4 Basaltic Rocks In general the basalts are satisfactory aquifers and considerable amounts of groundwater occur in weathered zones both near the surface and between successive lava flows. Water also occurs in fissures and fractures but it is not found in the massive unweathered rock (du Preez, 1949). Groundwater may also occur at the base of the volcanic succession trapped in the underlying weathered rock. Numerous springs and seepages emerge along the margins of the lava flows. They vary widely in yield and some flows are large and perennial.

The amount of water provided by the basalts depends on the size of the rock mass and on the degree of weathering; thus the Biu and Longuda basalt plateaux are more significant sources of groundwater than the smaller basaltic areas where the rocks have only local hydrological significance. In many places on the Biu Plateau considerable amounts of water occur in the weathered basalt, although there is much seasonal variation in the level of the watertable. The pyroclastic rocks north of Biu are highly porous and they give rise to several springs. Further east on the Biu Plains the basalts are generally thin and contain far less ground water. Most of the water in the area is derived from weathered Basement rocks beneath the basalt. On the Longuda Plateau groundwater occurs both at the base of the lava sequence and in weathered zones between successive flows.

Area 5 Chad Formation Groundwater is found under watertable or semi-confined conditions in the whole of the saturated section of the Chad Formation in the west and south of area 5, and in the saturated portion of the top 60-90 m (200-300 ft) of the Formation in the northeast. It occurs in lenses of gravel, sand and silt. Lines of equal depth to the watertable reveal a complex pattern of low ridges and troughs, the more important ridges occurring below the larger stream courses. This suggests that the ridges are formed by influent seepage from the stream channels. Unconfined aquifers are the most common source of supply tapped by wells and boreholes in the western and southern part of the area. There are also occasional semi- confined aquifers in the watertable and some isolated sand lenses within the thick clays contain pressure water. In the northeastern part there are 3 zones of confined aquifers which provide most of the borehole supplies. The middle zone occurs over a wide area between Damaturu and Lake Chad (see Text Map 10). The first published account of the hydrology of the Chad Formation in Nigeria was by Raeburn and Jones (1934) who were the first to suggest it might contain artesian water. The first artesian borehole was drilled by the Nigerian Geological Survey in 1946 and regional explora tion for artesian aquifers began in 1955. The results of production drilling were summarised by Barber (1965) who described the distribution of pressure water in the Chad Formation. Subsequently Miller et al. (1968) investigated the groundwater hydrology further with special emphasis on the flow life of the artesian system. The hydrology of the whole of the Chad Basin has been under a joint UNESCO/FAO investigation (Gischler, 1967) in an attempt to

81 assess the recharge potential more fully. Text Map 10 shows the western limit of pressure water derived from the Chad aquifers and also summarises the availability of artesian water from the middle zone aquifer.

Below Maiduguri Barber and Jones (1960) recognised 3 water-bearing zones in the Chad Formation which they called the upper, middle and lower zones. The middle and lower zones yield water under artesian conditions, while water has to be pumped from wells in the upper zone. At Maiduguri the upper zone aquifer occurs between 30 and 90 m (100 and 300 ft) below the surface. It consists of lenses of fine to coarse sand intercalated with clays and silts. Individual lenses are not thick and rarely exceed 4.5 m (15 ft). Elsewhere a similar series of sand and clay layers 15-180 m (50-600 ft) thick occur above the middle zone and these have been grouped with the upper zone at Maiduguri. The variations in depth to water in the upper zone show that groundwater highs occur along the edge of Lake Chad and along all the major rivers. A marked groundwater low extends from Gubio to a few kilometres northwest of Maiduguri. This suggests that water in the upper zone originates from Lake Chad and from the river systems, and that in the aquifer it flows away from the lake and towards the interstream areas. Recharge to the upper zone by this process depends on the seasonal flow of the river systems. The amount of recharge is not known. The withdrawal rate from this zone is likely to increase in the future and close attention will have to be given to the construction and spacing of boreholes if the balance between withdrawal and recharge is to be satisfactorily maintained. The lower zone aquifer has been identified between 420 and 480 m (l 380 and 1 580 ft) below the ground surface at Maiduguri but it seems to have a very limited lateral extent and has not been recorded elsewhere.

The middle zone of aquifers is the most important and the most extensive, and has a proved lateral extent within Nigeria of about 52 000 km2 (20 000 mi2). It is known to extend north into the Niger Republic and is believed to extend east into the Cameroon Republic. The zone varies in thickness from a very thin layer to over 120 m (400 ft), but over most of northeast Nigeria it is thought to be between 60 and 90 m (200 and 300 ft) thick. The depth from the surface to the top of the zone in the proved area ranges from 75-375 m (250-1 230 ft). The aquifers within the zone consist of fine to coarse sand and occur as interconnected lenses intercalated with clays and sandy clays. Surface flows can be obtained from the zone in approximately 31 000 km2 (12 000 mi2) of Bornu and Dikwa emirates. The highest positive head, recorded near Lake Chad, is 21 m (70 ft) above the ground surface; in some parts of the sub- artesian area the pressure surface is more than 60 m (200 ft) below the ground surface.

The recharge potential of the middle zone aquifer is not fully understood. Barber (1965) showed that there are 3 areas of intake to the middle zone and that the main directions of flow are towards the Mongonu area; the Damaturu/Magumeri and Bama/Gulumba areas form sub sidiary foci (see Text Map 10). Present evidence suggests that, although there is a large amount of water stored in the middle zone, the amount of water flowing through it is rela tively small. Miller et al. (1968) concluded that no significant amount of recharge reaches the middle zone in Nigeria. At the rate of withdrawal in 1965 (5.68 million litres or 1.25 million gal per day) they estimate that artesian water would continue to flow for at least 30 years from the moderate and high-yield areas of the middle zone at a rate of 2 273 litres (500 gal) per hour with boreholes 8 km (5 mi) apart. With boreholes 16 km (10 mi) apart, flows of at least 22 730 litres (5 000 gal) per hour could be maintained in the high-yield areas. In the low-yield areas artesian flows of 455-910 litres (100-200 gal) per hour could be maintained with boreholes 8 km (5 mi) apart.

Area 6 Recent Alluvium Groundwater in the recent alluvial deposits is mainly replenished from the surface flow of the streams. With seasonal streams the quantity of water and the length of time that the water is retained in the alluvium after surface flow ceases depends on the porosity, permeability, thickness and extent of the alluvium and the hydraulic gradient. In many streams water is retained in the alluvium throughout the year and these reserves can consti tute important sources of groundwater. Groundwater may occur in river alluvium under pres sure, but this is usually a very local phenomenon.

GROUNDWATER QUALITY

The chemical quality of groundwater is almost as important as its quantity, particularly if it is to be used for industrial purposes or for irrigation. De Preez and Barber (1965) have summarised existing information on the chemical quality of the groundwater derived from each of their Groundwater Areas and Barber (1965) has described the quality of the water from each of the 3 pressure aquifers in the Chad Formation. Most of the groundwater is of rela tively high quality; water unsuitable for human consumption is rare and hardly any sources are unsuitable for animal consumption. Many of the sources of groundwater are immediately

82 suitable for irrigation, and most could be used for irrigation of selected plants, providing leaching precautions and chemical corrections were made to allow for the interaction of the dissolved salts with the particular range of soils.

Apart from possible pollution by nitrates, the Basement Complex rocks provide good drinking water. The waters generally contain less than 200 ppm of dissolved solids and are either of the calcium or sodium bicarbonate type (du Preez and Barber, 1965). Waters from the Bima Sandstone and the Yolde Formation in area 2 are sodium or calcium bicarbonate types with little or no sulphate. Apart from some samples with excessive concentrations of iron, they are good drinking waters. The more saline, sodium-rich waters may have only limited appli cations for irrigation; hardness, alkalinity and iron concentration may limit their indus trial potential. A sample from the Gombe Sandstone at Gombe was of the calcium bicarbonate type and was low in dissolved solids. The concentration of iron was high; otherwise it was good-quality drinking water suitable for irrigation under most conditions. Analyses of groundwater for the Kerri Kerri Sandstone (area 3) indicate water of low salinity of the sodium-calcium bicarbonate type. Nitrate in some samples indicates probable pollution; unpolluted, these are good-quality drinking waters and are suitable for irrigation and for most industrial purposes. Analyses of only 1 sample are recorded from the Biu Plateau; it is a good-quality drinking water but industrial applications may be limited by hardness, alka linity and salinity.

Waters from the western half of the Chad Formation (area 5) are of the calcium-sodium bicar bonate type; they are low in dissolved solids and slightly alkaline. Apart from the pollu tion hazard, they are good drinking waters and are suitable for irrigation under most condi tions. They are also suitable for many industrial processes. The waters from the upper zone of confined aquifers are of the sodium bicarbonate'type (Barber, 1965). They are silica- rich, low in dissolved solids and slightly acidic. They are excellent drinking waters and are suitable for both industry and irrigation. Waters from the lower zone are low in total solids and are of the sodium bicarbonate type. They contain free carbon dioxide and are slightly acidic. They are good drinking waters and can be used for irrigation on all but clay soils. They are suitable for most industrial purposes, though high in iron content.

Waters in the middle zone range in salinity from 194 to 1 065 ppm. They are sulphate- bicarbonate or bicarbonate-sulphate types; free carbon dioxide is always present and these waters are therefore slightly acidic. Total alkalinity ranges from 98 to 292 ppm and total hardness from 18 to 320 ppm. Within this range Barber (1965) recognises 3 groups of ground water. Sulphate with subordinate bicarbonate waters occur north of Gudumbali; bicarbonate- sulphate waters predominate between Gudumbali and Dikwa; east of Dikwa bicarbonate waters with only a little sulphate predominate. The zones along which these waters meet are marked by chemical interfaces (see Text Map 10). All the waters from the middle zone are good or fairly good drinking waters, although high iron and manganese concentrations may need to be reduced if the supply is to be piped. Irrigation with these waters is usually difficult, and because of either corrosive effects, high salinity, hardness and alkalinity, or excessive concentrations of iron and manganese, they have only limited industrial applications.

Groundwaters from river alluvium are of the calcium bicarbonate type and are low in total dissolved solids. They are suitable for most uses. One disadvantage is that these shallow water supplies are liable to pollution where waste disposal is not controlled.

83 AREAS COVERED BY RECONNAISSANCE SOIL SURVEYS TEXT MAP II A 12*

SCALE 1:3.000.000

MILES 0 25 50 75

NgUTl

Mongonu (

H0waK

5 Song IcungoO ,13

Map Year Year of Reference Area Authors *£,& Publication 1 North-eastern Bornu 1959-60 G.M. Higgins. D.M. Ramsay. 14 I960 R.A. Pullan & P.N. de Leeuw Nfuru-Hadejia-Gurrnel 1961 R. A. Pullan IB 1962 3 Axare 1961 R.A. Pullan 19 1962 4 Poti»kum-Damaturu I9S9 W. A. Hope 20 1963 (provisional edition only) 5 Middle Gongola 1958-61 K. Klinkenberg. P. R. Tomlinson, 21 1963 (provisional G. M. Higgins & P. N. de Leeuw edition only) ___^^_ Main Road 6 Lau-Kaltungo 1964-66 K. Klinkenbert 36 1967 7 Lamewa 1966 G.M. Higgins 38 (draft only) i t i Railway 8 Maiduguri 1967 D.M. Carroll 40 1970 + + •+• + + + International Boundary 9 Gulumba 1967 R.A. Pullan 41 1969 10 Kirawa 1967 R.A. Pullan 42 1970 II Biu-Mubi 1966 D. M. Carroll & W. A. Hope 43 1970 12 Goniri 1967 K. Klinkenberg (inpr eparation) 13 Song 1967-68 W.A. Hope (inpr eparation)

10" 12° East of Greenwich 14"

D.O.S.(L.R.)3064Y Drawn and photographed by Directorate of Overseas Surveys, 1970

84 SOILS by D M Carroll and K Klinkenberg

INTRODUCTION The soil map at 1:1 000 000 (Map 3)presented with this report is largely based on reconnais sance surveys carried out by the Soil Survey Section of the Institute for Agricultural Research, Samaru, with assistance by the Department of Geography, University of Liverpool, and by the Land Resources Division of the Overseas Development Administration, Foreign and Commonwealth Office. Aerial photographs were used in drawing soil boundaries for the unsurveyed areas, enabling much of the information collected during the reconnaissance surveys to be extrapolated over the areas with less detailed information.

The survey cover published or in the press as Soil Survey Bulletins of the Institute for Agricultural Research is shown in Text Map IIA. In this report full use is made of the data published in these bulletins and also of unpublished material held in the Soil Survey Office. In all more than 1 100 soil profiles were described and analysed. The work of the many people who made the surveys is acknowledged, but responsibility for the correlation and final classification remains with the authors. Exchanges with pedologists from neighbouring fran cophone territories have taken place, which have been particularly helpful, as the classifi cation for the map is based upon the French system.

85 Figure 7 Generalised soil pattern

x X 00 * * x * x x ** VV^VÏ'WKS*»*

Rock Rocky Shallow and Well drained Poorly drained Soils with outcrops soils deep sandy soils loamy soils loamy-clayey soils lronpan

Topography Very steep Steep Undulating Oentle Nearly flat Flat

Profile development No No No Weak Moderate Oood

Clay content Very low Low Moderate Moderate-high Moderate

Mottles No No No No No-few Common-many Common-many

Ironconcret. No No No No-few Few Common Many

Llmeconcret. No No No No No Locally Locally

D.O.S 3099 G Soils in Relation to Soil-forming Factors

Forty units are shown on the soil map; each has its own particular pattern, often of a catenary nature. 'Catena' is a name given to an assemblage of soils occurring in a natural order in relation to the slope and that order is found over most of the unit. Topography has an important bearing on several soil-forming processes.

Some of these processes and the resultant soil patterns are illustrated in Figure 7 which gives a schematic view of the different topographic conditions that exist on rocks such as granite and the mineralogically similar Bima Sandstone.

In hilly areas the rock is mainly subject to physical weathering; the resulting debris is moved downslope by gravity and by rainwater. This disintegration continues and the weather ing products are gradually moved further down the slope. The hills are therefore often surrounded by areas of sandy wash. These wash soils have little or no differentiation within the profile and they contain very small amounts of clay because the clay is normally carried away by water moving laterally through their profile.

Further away from the hills, where slopes become gentler, the soil material is normally developed in situ. Here clay is leached from the upper parts of the soil and redeposited in subsoil horizons. Part of the clay in these horizons may also be derived from higher up the slope.

The role of groundwater becomes increasingly important when the slopes become gentler. Soils in which groundwater is present for some time of the year are grey or pale in colour and are normally mottled. Better-drained soils are often brown or reddish. Groundwater is also an important agent in the vertical and lateral movement of clay and some of the chemical consti tuents. Soils of lower slopes and plains are often richer in clay, calcium carbonate and iron concretions than are upper slope soils. Although this sequence refers specifically to particular geological conditions, under different circumstances some of the important features are often found again. These are particularly:

1. increasing clay content downslope;

2. colour changes from red and brown to grey, downslope;

3. accumulation of iron in lower-slope and flat areas;

4. accumulation of calcium carbonate in lower-slope soils. The pattern shown in the diagram is always subdivided into several mapping units, the compo sition of which depends only on how the different components occur together in the terrain.

Soils with ironpan, for instance, occur only on old, stable, land surfaces, such as those around Gombi and Askira. Units with hill and wash soils are almost absent from the northern part of the area, because only unconsolidated sediments of the Chad Formation occur here. The soils of the dunefield, which extends over a large part of the Chad Formation, also have a catenary arrangement similar to that already described: colour changes and increases in clay and calcium carbonate downslope. In relatively flat areas, where the run off is naturally slow, poorly drained soils predominate. Important differences from the schematic outline shown are caused by differences in parent material. Soils formed from basalt have a similar arrangement, but they tend to be richer in clay and organic matter, while soils with iron concretions are infrequent and ironpan is completely absent.

The Kerri Kerri Formation consists largely of very thick permeable sandstone deposits and poorly drained soils are almost absent. The soils are chemically poor, because the material has been subject to several cycles of weathering in the past.

The shales in the Gongola and Benue Valleys and some lacustrine clays near Lake Chad are rich in the clay minerals of the montmorillonite type. The swelling and shrinking properties of this mineral have a strong influence on soil properties: the soils show deep, wide cracks during the dry season and the soils have little or no vertical differentiation.

Climate is, with topography and geology, one of the most important soil-forming factors. Over the larger part of the area rainfall is sufficient to allow for a downward movement of clay and other materials, while most soluble salts are completely removed through the drain age system. Rainfall gradually decreases northwards and below 500 mm (20 in) the leaching

87 of clay becomes very small. In the far north the rainfall is not sufficient for the develop ment of a complete drainage network and water is found only in local depressions, where salts accumulate by evaporation. Calcium carbonate and sodium salts occur frequently in this part of the project area. If sodium ions are present in quantity, they may have a harmful effect upon the soil structure.

The remaining soil-forming factors, time and biotic influences, are of relatively less importance in North East Nigeria. In recent sediments, such as riverine alluvium, no soil profile development has yet taken place, while on some older land surfaces sufficient time has passed to allow for the formation of an ironpan. Vegetation has contributed to soil formation particularly on the fringes of Lake Chad, where organic deposits occur. The activity of man has in several cases accelerated erosion and thus reduced the soil depth.

CLASSIFICATION Principles The classification adopted is based upon that used by pedologists in neighbouring francophone countries (Aubert, 1964; 1965). The French system is followed as closely as possible, but in 1 or 2 cases new categories are introduced to accommodate particular soils occurring in the project area.

The French classification is largely based on the type and degree of profile development. Important parameters taken into account at a high level of classification include cation exchange capacity, base saturation, distribution of clay, amount and distribution of organic matter, sodium content and pH, as well as the occurrence of concretions. Soil depth, texture and colour are properties used at lower levels of the classification.

Klinkenberg and Higgins (1968) discussed D'Hoore's legend (1964) of the soils map of Africa, as far as it applies to the northern parts of Nigeria.' In that legend a differentiation based on parent material was made at high level, because information on other aspects was insufficient. In the present report parent material is of intermediate importance in the classification. Soils separated at high levels of the classification may therefore occur together on 1 parent material.

In the French classification classes are recognised by the mode and intensity of evolution. The classes are divided into sub-classes on differences in pedo-climate, while the sub classes are divided into groups on the basis of the presence or absence of certain diagnostic horizons (D'Hoore in Moss, 1968). Table 4 shows the parts of the classification relevant to North East Nigeria. It will be noted that sub-groups are shown only for the Leached Ferruginous Tropical Soils, emphasising the importance of this group of soils in the project area. Raw Mineral Soils (R) i This class consists of rock outcrops and debris derived from them. D'Hoore (in Moss, 1968) would call most of these 'non-soils' . The major characteristic is the almost complete lack of soil development. As this class mostly occurs in steep areas, weathering products are rapidly removed. Weakly Developed Soils 1. Soils of erosion (We) These very shallow soils are often stony or rocky and have little or no profile differentiation. They are often developed on steep slopes and overlie solid rock within 30 cm (12 in) of the surface. Soils of this group are formed on granite of the Basement Complex, on sandstone, on basalt or on ironpan; they are never found over shales or unconsolidated sediments. They characteristically occur on eroded upper slopes in conjunction with Raw Mineral Soils or Non-Leached Ferruginous Tropical Soils, but they are not sufficiently extensive to be mapped separately.

2. Soils of deposition These soils are usually coarse-textured and often retain their original sedimentary stratification. Profile development is confined to a small accumulation of organic matter at the surface. They are found on a wide range of unconsolidated parent materials: on aeolian sands, on pediment deposits and on riverine, deltaic, lacustrine or lagoonal alluvium.

In alluvial areas the Weakly Developed Soils are normally associated with Hydromorphic Soils which form over the finer-grained deposits; in the north they also occur with Halomorphic

88 TABLE 4 The main elements of the French soil classification

Class Sub-class Group Sub-group

Raw Mineral Soils Non-climatic Erosion

Weakly Developed Soils Non-climatic Erosion

Deposition

Vertisols Topomorphic

Lithomorphic

Isohumic With saturated Semi-arid Brown Soils Soils exchange complex

Mull Soils Tropical Eutrophic Brown Soils

Sesquioxide Soils Ferruginous Tropical Soils Non- or Weakly Leached

Leached Without concretions With concretions or pan Hydromorphic on poor materials

Halomorphic Soils

Hydromorphic Soils Organic

Mineral Normal

Vertic

Note: The units shown in italics are relevant to the project area. Soils. Local alluvium is found throughout the area, but it can rarely be shown on small- scale maps.

On pediments there is a gradual transition from Weakly Developed Soils to Non-Leached Ferruginous Tropical Soils. The soils of the dunefield in the extreme north of the area have a very low clay content, which is reflected in their poor profile development. Visiting French pedologists (Gavaud, Bocquier and others) regard some of these soils as transitional between Weakly Developed Soils and Semi-arid Brown Soils. On the soil map they are indicated by the symbol Wa.

Vertisols The Vertisols are fine-textured soils with coarse prismatic or blocky structure; they are generally dark in colour. The soil shrinks and swells seasonally and large cracks develop during the dry period; surface soil is moved down the cracks, causing a markedly homogeneous profile. At a depth of 100-120 cm (3-4 ft) which approximates to the depth of regular wett ing and drying, the soil peds are normally polished and grooved; this phenomenon, known as 'slickensides' is typical of the Vertisols. The soil surface may have a wavy 'gilgai' micro- relief. These distinctive properties are caused by the high content of expansible clay in these soils.

The Vertisols often have a slightly to strongly alkaline reaction, although slightly acid soils are also found. Most of the alkaline soils contain calcium carbonate concretions and some soils have gypsum crystals. Although the Vertisols are generally dark-coloured, their content of organic matter is low (0.3-1.5 per cent organic carbon). These soils contain more than 30 per cent clay and have a cation exchange capacity in excess of 30 meq per cent soil. They are rich in bases, particularly calcium and magnesium. Their sodium content is often high, but the exchange complex is only rarely more than 10 per cent saturated with this ion.

The class of the Vertisols has recently been reviewed by Dudal (1965). They develop only in fine-grained parent materials under conditions of poor internal and external drainage where large quantities of bases can accumulate. They form in areas with semi-arid to sub-humid climates where the rainfall is of a seasonal nature and the total precipitation is normally between 500 and 1 000 mm (20 and 39 in). The associated vegetation is often tall grassland or Acacia savanna woodland. . Two sub-classes are recognised: Topomorphic and Lithomorphic Vertisols. 1. Topomorphic Vertisols (Vt) These soils are formed in flat areas without good external drainage, where the pedo-climate is wet for much of the year. Their main occurrence is on fluvial deposits north of Numan and on lacustrine deposits to the south of Lake Chad.

They are nearly always very dark in colour and they are sometimes mottled. They gradually merge with Hydromorphic Soils. 2. Lithomorphic Vertisols (VI) These soils are mainly developed from shales of the Cretaceous marine facies on more or less undulating terrain. As they occur on gentle to moderate slopes, they have a better external drainage than the Topomorphic Vertisols and their colours are not quite so dark.

Transitions between Lithomorphic Vertisols and the Hydromorphic sub-group of the Leached Ferruginous Tropical Soils are known to occur. In areas with rapidly alternating beds of sandstone and shale the soil pattern in which the Vertisols occur can be extremely complex.

Isohumic Soils Only 1 group of this class is found in North East Nigeria: Semi-arid Brown Soils. This group is characterised by a homogeneous and deep penetration of organic matter. The total amount is often quite small and probably derived from decaying roots, and the asso ciated sparse vegetation contributes very little surface litter. The exchange complex is saturated with calcium and the soils often contain calcium carbonate concretions or crusts. Many of the soils show an increase in clay content with depth, not as a result of leaching, but by new clay formation. In many cases the soil has well developed blocky or prismatic structure.

The distinction between Semi-arid Brown Soils and Non-Leached Ferruginous Tropical Soils is not very clear in the literature. Klinkenberg and Higgins (1968) mapped most of the soils in the Damaturu area as Subarid Brown Soils, but visiting French pedologists have indicated that

90 most of these soils are better classified as Non- or Weakly-Leached Ferruginous Tropical Soils, mainly because they show some translocation of iron in the profile.

In the present report only soils which combine the absence of gley with the presence of calcium carbonate assumulation are considered as Semi-arid Brown Soils. They occur locally in depressions in the Damaturu area and are somewhat more frequent in the Hadejia area. The carbonate accumulation is normally in the form of concretions, but pseudomycelia and crusts are also seen.

Gavaud (personal communication) regards the soils of the dunefield in the extreme North East as transitional between Semi-arid Brown Soils and Weakly Developed Soils, mainly because of their uniform brownish colour. They are not always fully saturated however and they do not contain calcium carbonate.

Mull Soils This class is represented by the group of Eutrophic Brown Soils (E), the central concept of which was discussed by Maignien (1963). The structure of these rather fine-textured soils is clearly expressed, being usually granular in the surface horizons and weakly subangular blocky below. The organic carbon content is high (about 2-3 per cent). The red hues and strong colours are caused by the liberation of free iron oxides. The clay minerals are mostly 2:1 lattice types and the soil has abundant reserves of weatherable minerals. The soil reaction is neutral and the cation exchange capacity is 15-25 meq per cent soil. They are rich in bases, particularly calcium and magnesium, and base saturation is usually more than 50 per cent.

The Eutrophic Brown Soils are developed only on basic parent material. This mostly consists of basaltic rocks, although there are some outcrops of gabbro and epidiorite within the Basement Complex. The physical nature of the rock appears to be an equally important factor in the formation of-these soils as they are generally not found over solid lava. The average annual rainfall of the order of 1 000 mm (39 in), concentrated into a 5-month rainy season, is apparently not high enough to alter and leach solid basic rock.

The Eutrophic Brown Soils occur mainly on better-drained sites. Some contain iron concre tions and represent a transition to Ferruginous Tropical Soils, while on lower slopes, under conditions of impeded drainage, vertic properties are developed and the Eutrophic Brown Soils are replaced by the vertic group of Hydromorphic Soils or by Vertisols.

The most extensive areas of Eutrophic Brown Soils are found on the Biu Plateau where they are associated with, shallow and stony soils on volcanic cones and on rocky scarps.

Ferruginous Tropical Soils The Ferruginous Tropical Soils are a sub-class of the Sesquioxide Soils. They are chiefly characterised by the accumulation of free iron oxides within their profile, particularly in the deeper horizons; they often have strong yellowish or reddish brown colours and regularly contain iron concretions. The organic matter content is very low and humus is rapidly decomposed (Dabin, 1967). These soils contain illitic as well as kaolinitic clay minerals; their cation exchange exchange capacity of 20-40 meq per cent clay is relatively high. Base saturation is also moderately high to high, usually being greater than 40 per cent. There are appreciable reserves of weatherable minerals in some of these soils.

Segalen (1967) has recently reviewed the factors affecting the formation of these rather varied soils. It appears that a total annual rainfall of over 500 mm (20 in) is necessary before a soil will develop the properties of a Ferruginous Tropical Soil. The pronounced seasonal changes of climate, when a wet, reducing pedo-climate is followed by dry, oxidising conditions, strongly influences the redistribution of sesquioxides in the profile. Generally soils in the south of the country are more strongly leached and consequently more acid and base-unsaturated than those on similar parent materials in the north.

The first signs of leaching in the profile are the appearance of thin bands of lamellae, of iron and clay accumulation. Eventually the soil may show a clear textural B horizon and evidence of clay translocation such as clay skins. In many soils, particularly under poorer drainage conditions, iron deposition takes the form of mottles or concretions. If deposition continues for long periods an ironpan may be formed. Also, under poor drainage conditions, accumulation of calcium carbonate is often observed.

91 Two major groups of Ferruginous Tropical Soils are recognised: Non-Leached and Leached Ferruginous Tropical Soils. 1. Non-Leached Ferruginous Tropical Soils (Fn) The clay content of these soils is approximately constant throughout the profile, but there may be translocation and accumula tion of iron and development of soil structure.

Two families of this group can be distinguished. Non-leached soils are common on the aeolian drift which overlies the Chad Sediments in many places. The material is very sandy and therefore a textural B horizon would not easily develop. Lamellae are common features of these dune soils. The other family of non-leached soils is found in colluvial material, which surrounds hilly areas on both Basement Complex and sandstone formations. These soils are also very coarse, but some iron concretions are regularly observed.

2. Leached Ferruginous Tropical Soils This very important group is further divided into 4 sub-groups, all of which have a textural B horizon. a. Without or with few concretions (Fl) In these soils the translocation of iron is only apparent in the form of a colour B horizon or as mottles. The mottles may harden into concretions which are never frequent. The soils without concretions gradually merge with the Non-Leached Ferruginous Tropical Soils on the one side and with the concretionary and hydromorphic ones on the other. They normally occur on gentle slopes over sands, sandstones and granite. b. With concretions (Fc) Here the iron accumulation is very strong and an almost con tinuous layer of iron concretions is found at a depth varying from 45-130 cm (18-50 in). This layer sometimes hardens to form an ironpan. This sub-group is restricted to erosion surfaces, where soil formation has continued uninterrupted for long periods. Locally, at breaks of slope, calcium carbonate concretions are found associated with the iron concretions.

C. Hydromorphic (Fy) These soils shows some properties which may be attributed to hydromorphic conditions. They often have a clear distinction between the textural B horizon and the overlying leached layer, which may be bleached. The colours are always pale or grey and the soils are mottled at a relatively shallow depth. They often contain calcium carbonate concretions and are highly saturated. They gradually merge into leached Halomorphic Soils, from which they are distinguished by the lower sodium content. Olive- coloured soils, with or without calcium carbonate concretions, formed from mudstones, can be regarded as transitional between Vertisols and Hydromorphic Ferruginous Tropical Soils. The Hydromorphic Ferruginous Tropical Soils mainly occur in flat areas with very slow external drainage. d. On poor material (Fp) These soils occur only on material derived from the Kerri Kerri Sandstone. This material has passed through several cycles of weathering and the cation exchange capacities of 17-22 meq per cent clay are low for Ferruginous Tropical Soils. The great depth and red colour of these soils suggests that they are only marginal members of this sub-class. A textural B horizon exists, but at greater depth (2-3 m) (7-10 ft) than is considered normal. These soils cannot be satisfactorily classified in the French system. In the past Nigerian workers have classified them as Ferrallitic Soils (Tomlinson, 1967) and Ferrisols (Klinkenberg and Higgins, 1968). It is now felt that they have more the properties of the Ferruginous Tropical Soils but, to indicate their special characteristics, the subdivision of Ferruginous Tropical Soils on poor material is proposed.

Two families can be distinguished: one over ironpan or iron concretions near Potiskum and a non-concretionary family in the Wawa Bush (Land Systems Illbl and 2).

Halomorphic Soils Halomorphic Soils are those whose characteristics are mainly determined by the presence in the profile of soluble salts and high levels of exchangeable sodium. They have not been studied in great detail in North East Nigeria, but 3 groups are known to exist: Saline Soils, Non-Leached Alkali Soils and Leached Alkali Soils.

1. Saline Soils Saline Soils have a conductivity (in 1:5 water suspension) which is more than 7 millimhos per cm at 25°C. They appear to be confined to the extreme north of the country, although slightly saline soils occur elsewhere as subdivisions of other soil classes. These soils commonly have salty crusts or efflorescences, particularly of sodium sulphate. 92 2. Non-Leached Alkali Soils The clay complex of these soils is dominated by alkaline cations, which disperse the clay fraction, giving rise to very compact profiles. The most effective cation is sodium, but it has been claimed that magnesium may behave similarly (Ehrlich and Smith, 1958). The clay content of the non-leached soils is approximately con stant throughout the profile. They are mostly fine-textured, often with some hydromorphic or vertic properties. Transitions to the Vertisols are indicated on the map (Hv). Many soils also contain calcium carbonate concretions and transitions to the Semi-arid Brown Soils also exist (Ha).

3. Leached Alkali Soils This widespread soil group has the very characteristic morphology of the Solodised Solonetz. Similar soils have been described from other parts of the Chad Basin (Bocquier, 1964) and from many other tropical and temperate countries.

The profile consists of a thin, pale coloured, slightly acid, loamy sand surface horizon, which is very porous; there is a sharp boundary to a stronger-coloured, compact, strongly alkaline sandy clay, with well expressed columnar structure. At the base of this B horizon, carbonate concretions and pseudomycelia are commonly found and there is a gradual transition to the parent material. The exchangeable sodium content of these soils can vary widely and Coulter (1967) has noted that it bears little relation to their morphological development. It would appear that the commonly accepted limit of 15 per cent of the exchange complex being saturated with sodium is too high. Nigerian examples of this soil vary in the clarity of expression of the columnar structures and the analyses available tend to support Janzen and Moss (1956) in saying that the round-topped columns only develop when the exchangeable sodium percentage is greater than 10.

The Alkali Soils are found only on medium-textured deposits in the drier northeastern part of the area, often with a bare 'sheetwashed' appearance to the ground. The probable source of the sodium is the acid igneous rocks of the Basement Complex.

The Alkali Soils usually occur in association with non-alkaline Hydromorphic Soils and with Weakly Developed Soils.

Hydromorphic Soils The characteristic properties of the Hydromorphic Soils are caused by seasonal or permanent waterlogging. They are very variable and have been divided into 2 sub-classes: Organic and Mineral Hydromorphic Soils. 1. Organic Hydromorphic Soils (Yo) The upper horizon of these soils contains at least 20 per cent organic matter. They are restricted to the edge of Lake Chad, where the swamp vegetation provides the organic matter. The soils are often somewhat saline.

2. Mineral Hydromorphic Soils (Y) Soils of this sub-class have gley horizons, in which reduction is the dominant process, or pseudogley horizons, where mottles and concre tions of reoxidised compounds occur. These gley or pseudogley horizons are found either near the surface or at depth. Some soils contain carbonate concretions. Soils with well developed properties, such as textural B horizons, typical for other classes, are excluded from the Hydromorphic Soils.

Hydromorphic Soils generally form over relatively impermeable fine-grained parent materials, even on sites with fairly good external drainage. Such parent materials include the more argillaceous Chad sediments and colluvial products of basaltic origin. They also develop in poorly drained low-lying sites and they cover all but the coarsest-textured alluvial and deltaic deposits. In alluvial areas the Hydromorphic Soils are usually associated with Halomorphic Soils and with Weakly Developed Soils. Many alluvial areas are too small to be shown on the soil map. Transitions from Hydromorphic Soils exist:

to the Weakly Developed Soils, in more freely draining conditions; to the Hydromorphic sub-group of the Ferruginous Tropical Soils, when a textural B horizon is developed; to the Halomorphic Soils with increasing salinity and sodium content; to the Vertisols with increasing clay content and surface cracking. The transitions to the Vertisols are important enough to be shown separately on Map 3 (Yv). This transitional group has wide surface cracks, like the Vertisols, but the cation exchange 93 capacity is below 30 meq. These soils also are normally mottled to the surface and they often contain some iron concretions. They are common on the colluvial basaltic material to the northeast of the Biu Plateau and also in the Ngaje Plains in the far northeast.

The main characteristics and relationships of the soils described are summarised in Tables 5 and 6.

SOIL PATTERNS* Introduction

Most of the 40 units of the soil map are combinations of 2 or more categories of the classi fication. Normally only the 2 most important categories are indicated in the map symbol. In some cases the constituent categories are closely related, for instance when non- concretionary soils occur on upper slopes and soils with ironpan occur on lower slopes in the same area. In other cases 2 quite different soils may occur in close conjunction. This is due either to the presence of 2 or more different parent materials, or because recent erosion is breaking up an old landscape. In cases where contrasting categories occur together they are separated by a stroke in the map symbol, for example Pn/Vt. Basement Complex The soil patterns in the Basement Complex area are closely related to differences in landform. 6 main types of landform can be distinguished: Hills; Pediments; Undulating areas; Plains; Dissected areas; Alluvial valleys. There are not always clear-cut distinctions between the main types and gradual transitions occur frequently. The main different types of landform and their associated soil patterns are illustrated in Figure 8.

The hill complexes (Land Systems Icl to Ic5) and also the Hawal Escarpment (Land System Ic6) are dominated by rock outcrops, rubble accumulations and very shallow, stony soils. These are mapped (Map 3) as Raw Mineral Soils and Weakly Developed Soils of erosion (RWe). Locally deep pockets of sandy colluvial or alluvial material occur. In the larger valleys (Land Systems Id2 and Id8) and also on the pediments (Land Systems Idl and Idll) surrounding the hills, these colluvial and alluvial accumulations are often large anough to be shown on the map. The soils have little or no profile development and are mapped as Weakly Developed Soils of deposition and Non- or Weakly Leached Ferruginous Tropical Soils (WdFn). They are generally deep to very deep, well drained, coarse-textured (less than 20 per cent clay) soils and they normally contain unweathered quartz, feldspar and mica. The Weakly Developed Soils often retain their original stratification, while in the Non- or Weakly Leached Ferruginous Tropical Soils (example, Kaltungo Series) some iron concretions may occur. The degree of soil profile development on the pediments increases with distance from the hills: the Weakly Developed Soils are found close to the hills, the Non- or Weakly Leached Ferruginous Tropical Soils further away.

On very large pediments, such as those occurring to the west of the Mandara Mountains (Land System Id6), and on gently undulating areas (Land System Ia2) the soils have horizons of accumulation of clay and iron oxides and a considerable proportion of them can be classified as Leached Ferruginous Tropical Soils. Near rock outcrops Non- or Weakly Leached Ferruginous Tropical Soils (example, Kaltungo Series) and shallow soils (example, Busra Series) are common. On Map 3 this combination is indicated with the symbol FnFl. The most common soils are well drained, brown sandy loams (example, Barriki Series) which often con tain unweathered fragments of feldspar and mica lower in the profile. Locally, in areas of poor drainage, grey, mottled sandy clays or sandy clay loams are found. These sometimes contain calcium carbonate concretions and may have a prismatic structure (example, Burashika Series). They are classified as the Hydromorphic sub-group of the Leached Ferruginous Tropical Soils, but are generally not of sufficient extent to merit separating on the soil map. Only on the Butuku Plain (Land System Ib7) do these soils become dominant, where they occur together with Vertisols, to which they are related (VIFy on Map 3).

On old land surfaces, such as occur to the west and northwest of Mubi, soil formation has continued for a long time and the soils contain many iron concretions which are often cemented together to form ironpan. These soils are classified as Leached Ferruginous Tropical Soils with concretions (example, Gombi Series) and shown on Map 3 with symbol Fc in Land Systems Ibl and Ib2. They occur together with non-concretionary soils in Land System Ib3 and these are shown as FIFc. These old land surfaces are attacked by erosion in varying

•For each example, profile descriptions and analyses are presented as an appendix in Volume 5.

94 TABLE 5 Relations between soil, parent material and site

Alluvium Basement Cretaceous Transitional Lacustrine Clayey Sandy Kerri Kerri Basalt Complex Sandstones formations deposits High Low Chad Chad Sandstone rainfall

Steep R R R R

We We We We

Accumulating Wd Fn Wa

Fn Fl Fn

Upper slope Fn Fn E Fl ^^? Wd Wd Wd Fl Fn Fp

E Pn 1 ""\^H1 ~t»-^ " Middle slope Fl Fl Pp Lower slope Fl Fl ^^ "'VI VI Vt / Y Y / HI A Fp

Yv Vt /Tv Yv /Hv "alns wm Old surfaces Fl Fl Fp/c Fe Fe

Note: For an explanation of the symbols used, see Map 3. TABLE 6 Main characteristics of soil categories

CEC Organic Clay per per carbon Category content B horizon 100 g 100 g Sat PH in Structure (Map 3) ESP % soil clay topsoil % in B horizon (subsoil)

Wd Low Stratified Low Nil to very weak

E 25-40 Structural 40-100 0-1 6.5-7.5 2.0 Crumb at surface

Fn 20 Lamellae 30-80 30-100 0-2 6.0-7.0 0.7-0.0 Very weak

PI 20-35 Colour ) Moderate Textural) 20-70 40-75 0-1 5.5-7.5 0.3-1.7

Fp 15-25 Moderate 17-22 40-60 4.5-7.0 0-0.4 Weak to moderate

Pc 30-50 Ironpan 30-40 60-90 0-1 6.0-7.0 0.5-1.5 Moderate

Fy 30-50 Textural 15-30 20-70 60-100 0-10 6.0-9.0 0.5-1.5 Moderate to strong blocky

VI 35-75 No 30-50 50-100 50-100 0-10 6.0-9.0 0.3-2.0 Strong prismatic

Vt 50-80 No 30-40 40-50 80-100 5-10 7.0-8.5 0.3-2.0 Strong prismatic

Yv 35-70 No 15-30 35-45 80-100 0-10 6.5-9.0 0.3-1.5 Strong prismatic

Hv +30 No 15-30 40-100 100 10 6.0-10.0 0.1-0.4 Strong prismatic

H 10-30 Textural 100 10 6.0-10.0 0.1-0.4 Strong columnar

CEC: Cation exchange capacity in meq % soil/clay Sat: Base saturation % ESP: Exchangeable sodium % Soil patterns on Basement Complex Figure 8

Mapping Units Wd Fn

Fn (Kaltungo Series)

a Hills and pediments

Mapping Units Rwe FnFI

Fl (Barriki)

(Burashika)

+ + b (Gently) undulating areas

Mapping Units

Fc (Gombi) We Wd

•••*•*•.*•*•••••* *V»V***V*-**Y*.V *•••%• *••• * *

c Old surfaces

Mapping Units Fc/We We Fn Fc/We

d Dissected areas

DOS. 3099 H

97 degrees. In the Doksa Plain (Land System Ib4) the number of valleys with eroded soils is sufficient to be mentioned on Map 3 (symbol Pc/We). The soil patterns of the Tum and Zomba Plains (Land Systems Ib5 and Ib6) resemble those of the hill complexes previously described; erosion has almost completely destroyed the old surface and only shallow soils remain, although in the valleys there are colluvial accumulations of sandy material, with weak pro file development (WeFn on Map 3).

Some of the properties of the main soil classes found over the Basement Complex are sum marised in Table 7. Cretaceous Sandstones This section describes the soil patterns developed over the Bima and Gombe Sandstones and also those over the southwestern part of the Chad Formation in the area south of Gujba. The sandstone members of the transitional formations are discussed below..

The soil and landscape pattern over the sandstones are very similar to those on the Basement Complex. They are illustrated in Figure 9.

The hill complexes (Land Systems IIcl, 2 and 3) once again are dominated by rock outcrops, rubble accumulations and very shallow, stony soils. They are mapped as Raw Mineral Soils and Weakly Developed Soils of erosion (RWe). In the Gombe Hills (Land System IIc3) and the Korode Escarpment (Land System IIc2) ferruginised sandstone and ironstone are common on the upper slopes. In the Balbaya Plains (Land System IIb4) and the Kuma Plain (Land System IIb8) there is a linear pattern of alternating rock outcrops and shallow Ferruginous Tropical Soils (R/Fl).

Extensive pediment slopes are found only about the Filiya-Lamurde hill range and in the Gombe Sandstone areas (Land Systems IIb2 and IIb7). Around Gombe much of the colluvial material is derived from nearby occurrences of the Kerri Kerri Sandstone. The soils of these pediments are deep to very deep sands, with little to moderate profile development (example, Malori Series); they are mapped as Non- or Weakly Leached and Leached Ferruginous Tropical Soils (FnFl). They are sometimes underlain by shales of the transitional forma tions and they normally remain moist for a considerable time into the dry season.

In gently undulating areas (Land Systems Ilbl, Ilbll and Val) the soils are mainly sedentary and the profiles are well developed. Rock outcrops and shallow soils may be found on the upper slopes. The deeper soils are mainly sandy clay loams, changing in colour from reddish brown on the upper slopes (example, Busari Series) to light yellowish brown and grey with mottles on middle and lower slopes (example, Ninowa Series). In flat areas with poor external drainage finer-textured soils containing calcium carbonate concretions are found. These are classified as the Hydromorphic sub-group of the Leached Ferruginous Tropical Soils, but most of the soils in these areas belong to the normal sub-class without concre tions and are mapped as such (Fl). The soil distribution pattern is very similar to that over the Basement Complex, but grey soils are more common on the sandstone and the cation exchange capacity of the sandstone soils is slightly lower.

On older land surfaces mainly occurring in the eastern part of the area the soils are more strongly developed and contain iron concretions or even ironpan. They are classified as the concretionary sub-group of the Leached Ferruginous Tropical Soils; they are dominant in Land System IlblO (Map 3 symbol Fc) and occur together with non-concretionary soils in Land System IIb9 (symbol FIFc). In the Gumsuri Plain (Land System IIb3) several valleys with very shallow soils have been eroded into the plain and this area is mapped as Fc/We. Alluvial soils occur throughout the sandstone areas, but are mapped only where they are very extensive. Some of the properties of the main soils over the sandstones are summarised in Table 8.

Transitional Formations The transitional formations include the complex of marine and continental sediments laid down between the Bima and the Gombe Sandstones. They occur mainly in the Gongola Valley and on either side of the Filiya-Lamurde anticline. Lithologically they consist of shales, mudstones, sandstones and limestones, often in rapidly alternating succession. Because of these rapid variations in parent rock the soil patterns are often very complex.

Each of the rock types produces a distinctive soil. The shales normally give rise to Vertisols (example, Mutwe Series); olive-brown to grey-brown clay soils, which crack severely during the dry season, and which have a cation exchange capacity of more than 98 TABLE 7 Properties of soils on the Basement Complex

Organic Clay in Development Concretions CEC Sat ESP PH Soil Depth to carbon in B horizon of texture in Colour unit mottling topsoil (Map 3) B horizon iron carbonate in B horizon topsoil subsoil % %

Wd 5-20 Often Pale Variable None None stratified

Fn 5-20 Very weak Yellowish 10 cm Pew None 50-80 70-100 0-2 6.0-7.0 6.0-7.0 0-0.7 brown

PI 20-35 Very good Reddish 75 cm Few None 30-70 40-75 0-1 5.5-7.5 5.5-7.5 0.4-1.7 brown to grey

Fc 30-50 Very good Reddish 50-100 Many Locally 30-40 60-90 0-1 6.0-7.0 6.5-7.5 0.5-1.5 brown cm

Py 30-50 Moderate Grey 15-50 Few Common- 30-70 60-100 2-10 6.0-7.0 6.0-9.0 0.5-1.5 cm many

CEC: Cation exchange capacity in meq % clay Sat: Base saturation % ESP: Exchangeable sodium % Soil patterns on Cretaceous Sandstones Figure 9

Mapping Units

Fl (Ninowa)

a Hills and pediments

Mapping Units

b Gently undulating areas

Mapping Units

Fc (Gumsuri)

c Old surfaces with incised valleys

D.O S 3099 ] 100 TABLE 8 Properties of soils on sandstone (including Kerri Kerri)

Organic Soil Clay in Development Concretions CEC Sat ESP PH Depth to carbon in unit B horizon of texture in Colour mottling topsoil (Map 3) % B horizon iron carbonate in B horizon topsoil subsoil %

Wd 0-20 Nil Pale Variable No No

Fn 5-20 Nil or Red to 150 cm Pew No 30-45 40-60 0-7 5.8-7.0 4.8-6.0 0-0.5 very weak reddish brown

PI 20-40 Good Brown to 15 cm Pew No 20-40 40-100 0-1 6.0-7.5 5.4-7.0 0.3-1.5 grey to common

Fy 30-45 Good Grey 15 cm Common Common 20-45 80-100 1-10 5.8-7.0 7.0-9.0 0.5-1.5

Pp 20-45 Very deep Red No No No 17-22 40-60 0 5.8-7.0 4.5-6.0 0-0.4

CEC: Cation exchange capacity in meq % clay Sat: Base saturation % ESP: Exchangeable sodium % 30 meq per cent soil. Where limestone bands are present in the shale, calcium carbonate concretions are commonly found in the soil. Sometimes gypsum crystals are present, in which case the electrical conductivity is high.

An olive-brown sandy clay develops from mudstones and very fine sandstones. The cation exchange capacity is less than 30 meq per cent soil and only small cracks develop during the dry season. These soils have a strongly developed angular blocky structure as opposed to the prismatic structure of the Vertisols. They often contain calcium carbonate concretions. The textural B horizon is moderately to fairly well developed and ferro-manganese concretions are commonly found. These soils are classified in the Hydromorphic sub-class of the Leached Ferruginous Tropical Soils (example, Nono Series).

Leached Ferruginous Tropical Soils, without concretions, similar to those described in the section on the soils over Cretaceous sandstones, are found over coarser-textured sandstones within the transitional formations. There are also occasional outcrops of sandstone rock.

Complications occur when 2 different parent materials are found within 1 profile. This happens when material derived from l rock is washed down the slope and then overlies other material or when different strata alternate at very rapid intervals. Sometimes a Vertisol is found over sandstone, sometimes a coarse-textured profile over shale. A mottled sandy clay loam commonly overlies a strongly structured clay with calcium carbonate concretions (example, Zangaya Series). This soil is also classified in the Hydromorphic sub-class of the Leached Ferruginous Tropical Soils.

The complexity of the soil patterns depends largely on the angle between the surface and the dip of the geological strata. Where this angle is very small the soils are normally rather uniform, but where it is large the variation in soils can be very rapid. Some examples of this are shown in Figure 10. The properties of the main soils are summarised in Table 9.

In Map 3,4 different symbols are used for the soils over the transitional formations, depending on the relative abundance of the component soils. In the Wagur Plains (Land System IId4) the Vertisols are dominant and the area is therefore mapped as VIFy, while further south in the Numan and Dadiya Plains (Land Systems Ildl and IId2) and also in the Dusu Plains (Land System IId5) the Vertisols are not so extensive and the Hydromorphic sub class of the Ferruginous Tropical Soils becomes the more important and the unit is given the symbol FyVl. In the Bajoga Plains (Land Systems IIb5), where shales are of very minor extent, there are only few Vertisol occurrences; the main soils belong to the Hydromorphic and non-concretionary sub-groups of the Leached Ferruginous Tropical Soils (FIFy). The Bajiram Plain (Land System IId3) is covered by a clay deposit which is probably derived from the Longuda Basalt to the west; Vertisols are developed on this clay and other soils are almost completely absent (VI).

Kerri Kerri Sandstone The Paleocene Kerri Kerri Sandstone is in some places, particularly in the north, strongly ferruginised or capped by ironpan. Over most areas however the rock is covered by a thick mantle of loose material and only rarely outcrops. The mode of deposition of the surface layers is unknown, but a dune pattern, only visible on the aerial photographs, suggests an aeolian reworking of the material. The material has undergone several cycles of weathering and this, in conjunction with its great thickness, is of great importance in determining the character of the soils. Only in the north, around Potiskum, is the ironpan extensive and the cover of reworked material rather thin. Even there, some of the soil properties are caused by the material undergoing several cycles of weathering.

The soils over the Kerri Kerri Sandstone are generally of very great depth, red in colour, and have a cation exchange capacity of 17-25 meq per cent clay (eg Wawa Series). These properties are characteristic of the Ferrallitic Soils, which are normally found under much wetter climates, but other properties, such as moderate base saturation and the presence of a textural B horizon, are typical of Leached Ferruginous Tropical Soils. It would appear that the soils have developed during wetter periods in the past, but are now exposed to pedogenetic processes that would result in Ferruginous Tropical Soils. After discussions with French pedologists it has been decided to classify and map these soils as Ferruginous Tropical Soils on poor material (Fp on Map 3). The textural B horizon is at great depth and can only be discerned in very deep profiles. The increase of clay with depth is shown in Figure 11. There is very little or no variation in soils at different positions along the slope, because the watertable in this permeable material is at very great depth and all soils are freely to excessively drained. 102 Soil patterns on transitional formations Figure 10

Mapping Units VIFy 1 -|

- Fy Fl - VIFy

Sandy soil Non-cracking clay rrCrackinr g clay

Shal' c J\ Mudstone 'i- Sandstone f Limestone ,./ Sandstone Shale a Moderately homogeneous patterns

Mapping Unit VIFy

Non-cracking clay

Mixed soil Cracking clay Mudstone Sandstone '

Sand over clay Sandstone'

Mudstone b Complex pattern Sandstone'

Mapping Units RWe VI Longuda Plateau Banjiram plain

between Longuda Plateau

D.O.S. 3099 K

103 TABLE 9 Properties of soils on transitional formations

Soil Concretions CEC Organic Development PH unit Clay in of texture Sat ESP carbon (see B horizon in Colour Mottling Structure soil clay in foot % B horizon iron carbonate topsoil subsoil topsoil note) in B horizon %

1 20-40 Good Brown to Common Moderate Few to No 5-15 20-40 40-100 0-1 6.0-7.5 6.0-7.0 0.3-1.5 grey blocky common

2 25-60 * Grey over Many Strong Pew to Variable 15-30 40-60 70-100 3-10 5.0-7.5 6.0-9.0 0.5-1.3 olive blocky common brown

3 25-45 Moderate Olive None Strong Pew to Variable 20-30 40-70 80-100 4-7 6.0-7.0 8.0-9.0 0.5-1.3 brown blocky common

4 .35-75 No Grey Pew Strong Very Variable 30-50 50-100 50-100 0-10 6.0-8.0 6.3-9.0 0.3-2.0 brown prismatic few

1 Soil over sandstone (PI) CEC: Cation exchange capacity in meq % soil/clay 2 Sandy soil over clay (Py) Sat: Base saturation % 3 Clay soil over mudstone (Fy) ESP: Exchangeable sodium % 4 Clay soil over shale (Vt)

*Two parent materials in 1 profile Clay content of three soils on Kerri-Kerri Sandstone Figure 11

10 15 20 25% clay 1 1 1 1

100

ISO

200

250

300

350 \-

400 \-

450

500

D.O.S. 3099 L

105 This kind of soil is dominant throughout the southern part of the Kerri Kerri Sandstone area, and covers most of Land Systems Illbl and IIIb2. Locally (as in Land System IIIb3) areas of ferruginised sandstone emerge through the loose material. These are normally hilly features with rock outcrops and shallow soils, shown on Map 3 as Raw Mineral Soils and Weakly Developed Soils of erosion (RWe). In some of the deeper valleys (Land System Illdl) either a perched or permanent watertable is close to the surface and Hydromorphic Soils and Weakly Developed Soils are found (Y/Wd).

In the north, around Potiskum, the cover of loose material is very much thinner and the soils mostly overlie ferruginised sandstone or ironpan at shallow depth. They are still classified as Ferruginous Tropical Soils on poor material, but the underlying ironpan is indicated by the suffix 'c' in the map symbol: Fpc. This mapping unit also includes soils on similar sites in the Chad Formation (Land System Vc3). Areas where rocky soils predominate have also been separated (RWe).

The Kerri Kerri Sandstone is strongly dissected between Potiskum and Fika (Land System IIIcl) and near Yuli (Land System IIIc2). These areas are characterised by very steep rocky slopes and valleys with very deep sandy soils. The valley soils have little or no profile develop ment and these areas are therefore mapped as Raw Mineral Soils and Weakly Developed Soils of deposition (R/Wd).

Basalt The volcanic Biu Upland (Land System IVal) and the Longuda Upland (Land System IVa2) have many shallow and stony soils; the basic rocks do not appear to weather deeply under the prer vailing climatic conditions. The nature of the underlying rock greatly influences the resulting soil; where the parent material is a solid, blocky lava with weak jointing, a poorly drained firm clay with vertic tendencies results and where it is a tuff or agglomerate a better-drained friable loam, tending towards a Eutrophlc Brown Soil, is found. The various lava flows are separated by numerous small scarps where rock outcrops and shallow soils predominate. The same applies to the high, steep scarps, which surround the Plateaux in places. The volcanic cones of the Biu Hills (Land System IVcl) also have stony, shallow soils. These cones are surrounded by an area of deep, relatively stone-free red friable clays. These soils are freely draining, although they occur on very gentle slopes; they appear to be formed from reworked ash or tuff deposits. The cones on the Garkida Plain (Land System IVdl) and the Song Volcanic Complex (Land System IVd2) are associated with rocky rubble and shallow stony soils over lava.

Reddish brown or yellowish red loams and clays are also found on slightly elevated sites on the Biu and Longuda Plateaux. These Eutrophic Brown Soils are most common in areas of pyroclastic rocks and are also found on the flattish tops of lava flows, wherever weathering is strong enough to produce a deep soil (example, Pulda Series). In some localities the underlying rock is slightly ferruginised and the soils possess a weakly cemented concre tionary horizon, thus forming a transition towards the Ferruginous Tropical Soils.

Much of the Biu Upland consists of a series of basins where clayey colluvium covers the lava flows. The chaotic organisation of these deposits and the fact that they can be traced from volcanic craters suggests that they are formed, in part at least, by volcanic mudflows. There is a clear toposequence of soils in these gently sloping basins. The upper and middle positions are covered by brown, firm, imperfectly drained clays (example, Kuda Series); deep cracking, slickensides and other vertic properties are more strongly developed in the poorly drained clays of the lower slopes and very poorly drained soils with abundant calcium car bonate concretions occur in the bottom lands (example, Pawa Series). The Biu Plains (Land System IVbl) have poor surface drainage and give rise to grey cracking clays with many calcium carbonate concretions. The clays are frequently very compact and they may have appreciable sodium contents. They are classified and mapped (Map 3) in the vertic sub-group of the Hydromorphic Soils (Yv) (example, Gur Series). The soils are often stony and the surface may be covered with basalt rubble. In some areas large heaps of boulders cover the plains, forming shallow, stony soils. Some of the properties of the soils derived from basalt are summarised in Table 10, while the topographic relations are illustrated in Figure 12. As stated above, the soil patterns of the Biu and Longuda Uplands and the Biu Hills are very complex. Rock outcrops, Weakly Developed Soils of erosion, Vertisols and Eutrophic Brown Soils occur frequently. However, the frequency of the various groups varies from place to place. On Map 3 the dominant soil group is indicated. Rock outcrops and shallow soils are

106 TABLE 10 Properties of soils on basalt

Concretions CEC PH Organic Soil Clay in Development Depth to Sat ESP carbon unit B horizon of texture Colour mottling Structure soil clay in (Map 3) % B horizon iron carbonate topsoil subsoil topsoil in B horizon %

We 0-20 No Brown to - Weak, Few Few ------grey variable

E 30-50 No or weak Brown to - Crumb to Pew to None 10-15 20-30 60-80 0-1 6.5-7.0 6.5-8.0 1-3 red sub- common angular blocky

VI 40-55 No Brown to 20-50 cm Sub- Common Few to 20-40 40-80 80-100 0-5 6.5-7.5 7.5-8.5 0.7-1.5 grey angular common blocky to prismatic

Yv 45-60 No Olive to 10-30 cm Sub- Few to Many 20-35 40-70 80-100 1-5 7.0-8.0 8.0-9.0 0.4-1.0 grey angular common blocky to prismatic

CEC: Cation exchange capacity in meq % soil/clay Sat: Base saturation % ESP: Exchangeable sodium % Soil patterns on basalt Figure 12

Mapping Units

Tuff

a Biu Hills and surroundings

Mapping Units EWe

b Biu Upland

Mapping Units EWe RWe Yv

Pulda Series Kuda Series \ Gur Series

c Biu Upland and Biu Plain

O.O S 3099 M 108 dominant on the steep scarps: RWe. The flatter areas on the Plateaux are dominated either by Eutrophic Brown Soils or by Vertisols; but shallow soils remain frequent and the map symbols are VlWe and EWe.

The Garkida Plain and the Song Volcanic Complex are also mapped as RWe. Chad Sands and Clays (sensu stricto) In the chapter on geology the Quaternary Chad Formation was divided into 7 units. The soil patterns associated with these units are however more conveniently discussed as 4 groups:

sands and clays ("sensu stricto); sands, including wind-blown material and beach ridges; lagoonal clays; alluvial deposits.

The group of mixed sandy and clayey deposits is only of importance to the southwest of Maiduguri. In the west of that area the topography is gently undulating (Land System Val) and the soil pattern is very similar to that found over the Bima Sandstone. Most of the soils can be classified as Leached Ferruginous Tropical Soils without concretions (Fl on Map 3).

The eastern section (Land System Va2) is almost flat and the drainage is impeded. The soils are dominantly grey, mottled sandy clay loams with a well developed structural B horizon, (example, Kirik Series). In local depressions and drainage lines the contrast between structure in upper and lower horizons is even greater; it is caused by an accumulation of sodium (example, Latan Series). These soils are mapped as the Hydromorphic sub-class of the Leached Ferruginous Tropical Soils and Leached Halomorphic Soils (FyHl).

The upper sections of the larger valleys (Land System Va3) are more freely drained and the soils are Leached or Weakly Leached Ferruginous Tropical Soils (FnFl). In the lower parts of these valleys (Land System Va4) alluvial soils predominate.

Sandy facies of the Chad Formation This group consists mainly of aeolian deposits, but also included are the Bama and Ngelewa Beach Ridges and their associated lacustrine sands. The aeolian deposits give rise to different types of terrain, varying from a relatively featureless plain west of Maiduguri, through irregular hummocky dunes in the northeast to regular, high, longitudinal dunes between Azare and Geidam. In some places fluvial activity has effectively altered the appearance of the dunes. Sometimes only the valleys between the dunes are filled with alluvial deposits; elsewhere the dunes are eroded and only remnants remain within alluvial areas. The sandy nature of the material is of great importance in determining the soil properties because the low clay content precludes the easy formation of pedologically significant B horizons. In these areas, rainfall is also often too low to allow for the movement down the profile of clay and other materials and it is not always sufficient for the formation of a complete drainage network. Water tends to accumulate in local depressions from which it evaporates, leaving accumulations of calcium carbonate and salts giving rise to Hydromorphic and Halomorphic Soils. These soils are particularly fre quent in the vicinity of Lake Chad and the main river systems. Their frequency is partly caused by the locally higher watertable, but also by seasonal flooding of the rivers inundat ing their surrounding areas, when deposition of alluvium usually takes place.

The general soil pattern is therefore a variable one of sandy soils alternating with Halomorphic and Hydromorphic Soils in the depressions. In some cases the material in the depressions is related to the sands; in other cases it is alluvium of quite a different nature.

With increasing rainfall, the sands show a gradual increase in profile development, but in some places, for example where erosion has taken place, there is no soil profile development.

In the extreme north and northeast where the rainfall is less than 500 mm (20 in) the dune soils show little or no profile development; they are very coarse-textured with a uniform brown colour (example, Gudi Series) and may be regarded as transitional between Weakly Developed Soils of deposition and Semi-arid Brown Soils. In the depressions there are grey, mottled loamy sands to sandy clay loams which contain calcium carbonate concretions and which have high pH and high sodium contents. These depression soils are classified as Halomorphic Soils. They are of very limited extent in Land Systems Vdl, Vd3 and Vd6 and are therefore not shown in the map symbol Wa. Land Systems Vd2, Vd7 and Vbl have a larger extent of Halomorphic Soils in the depressions and these systems are mapped as WaH.

109 The soils of the Bama and Ngelewa Ridges (Land Systems Vd4, Vd5 and Vel) are sands and gravels, which retain their original sedimentary stratification. They are mapped as Weakly Developed Soils of deposition. In the southern part of the Ngelewa Ridge (Land System Ve2) Halomorphic Soils are relatively common in the depressions and this area is therefore mapped as WdH. The Halomorphic and Weakly Developed Soils are developed from the same material in this mapping unit (Map 3) and should not be confused with some alluvial areas (H/Wd), where the Halomorphic Soils are found on clayey alluvium and the Weakly Developed Soils on more sandy material.

When the rainfall is more than 500 mm (20 in) per year, thin irregular bands of iron and clay accumulation start to appear in the dune soils. These soils vary in colour from red or brown on the upper slopes (example, Gulumba and Birnin Series) to brown or grey-brown on the lower slopes. They are classified as Non- or Weakly Leached Ferruginous Tropical Soils. In the south, depressions and small valleys have either brown soils with calcium carbonate concre tions or grey mottled soils; they are classified as Semi-arid Brown Soils (example, Jigilin Series) and as Hydromorphic Soils respectively, but they are of limited extent only. This arrangement of soils (indicated by symbol Fn) occurs in the longitudinal dunefield of Land Systems Vc2 and Veil, as well as in the rather flat lacustrine sand area of Land Systems Vd8 and VdlO.

In the north the dunes are partially flooded by water from the Hadejia and Jamaare systems (Land System Vg2); the watertable in this area is consequently higher. Semi-arid Brown Soils, in association with Halomorphic Soils, occur frequently in the depressions: this area is shown on Map 3 as Fn/Ha. Further north, in Land Systems Vb2 and Vc8, the drainage system is irregular and incomplete; Halomorphic and Semi-arid Brown Soils also occur in the depressions, but they are not as common as in the area previously described. They are shown on the map with the symbol FnHa. Remnants of the longitudinal dunefield occur to the east of the Bama Ridge; the depressions between these dunes are filled with more recent sediments. In Land System Vhl these are lacustrine clays in which Vertisols are developed; this area is there fore mapped as Fn/Vt. In Land Systems Vh2 and Vh3 the depressions have mainly Hydromorphic Soils formed in alluvial deposits: Fn/Y.

The aeolian plain between Maiduguri and Damaturu (Land System Vc2) and the lacustrine sands to the southeast of Maiduguri (Land System Vd9) have a slightly higher rainfall than the areas previously discussed. The soil parent materials are also richer in clay and the pro files are consequently better developed. The reddish yellow colour B horizon is well established and some structure can also be observed. There is some increase in clay content with depth, but not enough to classify the soils as truly Leached Ferruginous Tropical; they are therefore mapped as transitional between the Non- or Weakly Leached and the Leached sub-classes (Fn-1 on Map 3). The profiles are gradually better developed from north to south (example, Masho Series) and there is also a notable decrease in base saturation from north to south. Small depressions in this area have Calcareous or Hydromorphic Soils but are generally too small to be shown on the map.

Some broad valleys are incised into the plain and these are filled with colluvial and alluvial material; in the upper reaches (Land System Vc6) the soils are generally similar to those found on the uplands, but some less-leached soils are likely to occur (FnFl). In the lower reaches of the valleys (Land Systems Vc5 and Vc9) the ordinary soil complexes of alluvial areas are found. Close to Maiduguri, in Land System Vc4, the aeolian cover is thin and discontinuous: in several places the underlying clays come to the surface. The soil pattern is somewhat com plex as transitional Ferruginous Tropical Soils occur on the aeolian material while the clays give rise to Hydromorphic and Halomorphic Soils. This area is shown on Map 3 as Fn-l/H.

The properties of the more important soils are summarised in Table 11.

Lagoonal Clays To the south of Lake Chad lagoonal clays were laid down over an irregular sandy surface. In many places the clay has hardened into shale. The thickness of the clay is variable and in places small sandy areas emerge from the flat plain. In the south the depressions of the Musgowa dunefield (Land System Vhl) are partially filled by the clay and it is likely that the sand islands are also remnants of a dunefield. They are however modified by wind and water erosion and in some cases sand has been transported by wind to form new dunes which are found on top of the lagoonal clay. The sandy areas provide living sites and some of them have been artificially raised (Connah, 1966).

110 TABLE 11 Properties of soils on sandy facies of the Chad Formation

Soil Clay in Concretions Organic Type of PH unit subsoil Colour Mottling CEC Sat ESP carbon in B horizon topsoil (Map 3) % iron carbonate topsoil subsoil % Wd 0-10 Sedimentary White to None None None - - - 7.0-8.0 7.5-8.5 0.1-0.5 stratification light grey

Wa 0-10 None Pale None None None - - - 6.5-7.5 7.5-8.5 0.1-0.3 brown

Fn 0-10 Lamellae Reddish None None None - 35-70 0-2 6.0-8.0 5.5-7.0 0. 1-0.3 (upper yellow slope)

Fn 5-15 Lamellae Very pale Common Few Locally 35-60 40-100 0-3 6.0-8.0 5.5-9.0 0.1-0.3 (lower brown slope)

Fn-1 15-25 Colour B Reddish None None Locally 20-40 40-100 0-3 5.0-7.0 5.5-7.0 0.2-0.6 yellow

A 15-25 Moderate Brown None None Many 50-100 100 1-6 6.0-7.5 8.0-9.0 0.1-0.3 Textural B

H 10-30 Variable Light Common Few Common to 40-100 100 >10 6.5-8.5 8.5-10.0 0.1-0.4 grey to to many grey many brown

CEC: Cation exchange capacity in meq % clay Sat: Base saturation % ESP: Exchangeable sodium % The clay content of the soils is nearly always greater than 40 per cent and frequently exceeds 50 or even 60 per cent (example, Ngala Series). All these clay soils crack severely during the dry season, but not all can be classified as Vertisols, as by definition Vertisols have at least 30 per cent clay and show phenomena such as gilgai or slickensides. According to an older definition (USDA Soil Survey Staff, 1960), they should also have an exchange capacity of at least 30 meq per cent soil. This appears to be a useful property in the area under discussion, for, where the exchange capacity is below 30 meq, slickensides or gilgai are not observed and the soils are mottled and often contain iron or manganese concretions (example, Dougouma Series). These mottled soils are classified as the vertic sub-group of the Hydromorphic Soils. Both the true Vertisols and the Vertic Hydromorphic Soils in this area frequently contain calcium carbonate concretions and they consequently have a pH ranging between 7 and 9. The amount of sodium present in the soils is higher than in many other soils, but sodium rarely occupies more than 10 per cent of the exchange complex and struc tures characteristic of Halomorphic Soils have not been seen.

The soils of the sand islands are completely different. They are pale brown fine sands with out profile development. Because of their recent reworking they are considered younger than other dune soils, which show seme profile development. They are classified as Weakly Developed Soils of deposition. In the transition zone between the sand islands and the clay there are shallow sandy clays overlying sand.

Three main soil patterns exist (see Figure 13): Vertisols with Weakly Developed Soils of deposition (VtWd) in the areas of lagoonal clays with sand emergents of Land Systems Vjl and Vj3; Vertisols (Vt) in uniform clay areas (Land System Vj2); and Vertic Hydromorphic Soils (Yv) in Land System Vj4.

The properties of the various soils are summarised in Table 12.

Alluvial Deposits Alluvial soils are found along nearly all streams and therefore in nearly all land systems. Often they are of very limited extent and cannot be mapped separately. In many other cases however the alluvial deposits are extensive enough to warrant mapping as a separate unit. Particularly large alluvial areas are found along the Hadejia river, in the delta deposits of the rivers Yedseram and Alo and along the river Benue. The properties of these soils can be very variable over small distances. The nature of the deposits along the smaller steams depends largely on the rocks traversed by them. For example, a stream flowing through a shale area but rising on sandstone will have sandy deposits, while a stream which has the larger part of its catchment on shales and mudstones will be characterised by more clayey deposits.

The basic pattern of alluvial deposits (Figure 14) is similar all over the world (Edelman and van der Voorde, 1963). Near the present and former river beds natural levees occur which are normally sandy to loamy in character. They occupy the highest part of the terrain; behind them are depressions, which may be flooded for a considerable time and where lakes form a common feature. These areas, known as backswamps, have generally fine-grained deposits.

The pattern is not always so simple, mainly because of changes in the course of the river. As the river gradually changes its course a complex of levees is built up. In the Hadejia river area and in the deltas of the Yedseram and the Alo the streams do not always have a definite course and the picture is even more complex, as illustrated in Figure 10.

The river beds normally consist of coarse or fine sand and this material can hardly be clas sified as soil. The levees have sandy to loamy material in which the original stratification is often clearly seen. The levee soils are well to moderately well drained and can be clas sified as Weakly Developed Soils of deposition.

The backswamps have fine-textured soils in a flat topography. The soils are therefore poorly drained, normally grey in colour and mottled to the surface. Some of them crack severely when dry and can be regarded as the vertic sub-group of the Hydromorphic Soils (example, Lamido Series). In the basins of the Hadejia, Gana, Yobe and Yedseram river systems the basin soils have high sodium contents and sometimes high salinity as well; they are classified as Halomorphic Soils (example, Adi Series). The basin soils of the Alo delta and of some of the smaller rivers normally contain calcium carbonate concretions but do not have high sodium content or a high salinity; they are therefore still classified as Hydromorphic Soils. It appears that Halomorphic Soils occur in alluvial complexes of rivers originating in Basement Complex areas. It is likely that some of the granites of that com plex provide a source of sodium.

112 TABLE 12 Properties of soils on lagoonal clays

Organic Soil Concretions CEC pH Clay carbon in unit B horizon Colour Mottling Structure Sat ESP % topsoil (Map 3) iron carbonate soil clay topsoil subsoil %

Vt 50-80 None Dark grey Pew Strong None Pew- 30-40 40-50 80-100 5-10 7.0-8.0 7.0-8.5 0.3-2.0 prismatic common

Yv 35-70 None Dark grey Many Strong Common Common 15-30 35-45 80-100 0-10 6.5-8.5 6.5-9.0 0.3-1.5 brown prismatic

Wd 0-10 None Pale brown None No None None 6.0-7.0 6.5-7.5 0.1-0.3

CEC: Cation exchange capacity in meq % clay/soil Sat: Base saturation % ESP: Exchangeable sodium % Soil patterns on sandy facies of Chad Formation Figure 13

Mapping Units Wa WaH Wd Yo Lake Chad

^.S^S?!^^

Dunes with few Halomorphic soils in depressions Dunes with frequent Halomorphic soils Beach Ridge in depressions

Mapping Units Fn(FnHa) Fn/Ha

Birnin Series Jigilin Series ^^rrr-^ Adi Series

; 7 i r:ï^^i;?~S5&Ss: ^^^^•f;iij-l-:l:}^^^^^^i^^M'M^. •;~?*JltfZ~jj •^>;--Ä^ ^S=" ii^

Dunes sand, soils with weak profile development As Fn, but with many Halomorphic soils in depressions

Mapping Units Fn-I FnFI Fn-I

Benisheikh Serie

Aeolian plain with weakly to moderately well developed soils Valley • infill of sandy soils with variable profile development

Soil patterns on lagoonal clays

Mapping Units Fn/Vt Vt/Wd Vt Vt/Wd Vt

^^l^gll^^^J^^^^

Shale Longitudinal dunes with day in depressions Cby plain with sand islands Clay plains Non-Leached Ferruginous Tropical soils and Vertisols in plain mostly Vertisols Weakly developed soils on sometimes vertic aeoiian material Hydromorphic soils

D.O.S. 3099 N 114 Soil patterns in alluvial areas Figure 14

• i

Swamps

c Complex delta area near Bama

a Simple pattern (Benue River)

River

- A* Upland Back-swamp Ridge/swale Back-swamp Levee Floodplain | I Upland8 I Back-swamp Levee b Cross-section A - B

d Complex pattern along River Yobe

River Old channel Old channel Old channels

Ridge/swale Dunes I Dunes Dunes I Dunes Floodplain D Floodplain Floodplain

Cross-section C - D

D.O.S. 3099 P

115 Most of the alluvial areas are represented on Map 3 as combinations of Weakly Developed Soils of deposition with either Hydromorphic Soils (Y/Wd) or Halomorphic Soils (H/Wd). The soil patterns in Land Systems Vfl, Vf2, Vf3 and Vf5 are extremely complex because they con sist of eroded dunes surrounded by alluvial deposits. Both the dunes and the sandier allu vial materials have Weakly Developed Soils of deposition, while on the finer-textured material there are both Halomorphic Soils and Vertisols. This complex is shown on the map with the symbol Wd/Hv.

In some parts of the Yedseram alluvial complex nearly all the soils are Halomorphic (Land Systems Vi5, Vi7 and Vi9); in the higher areas these are leached (HI), mostly of the Solodised Solonetz variety and in the backswamp (example, Limanti Series) the Vertic Halomorphic Soils (Hv), are common.

In the Giwano Plain (Land System IIa6) a thick layer of clay has been deposited, probably by an old course of the river Gongola. On this material true Vertisols are developed (Vt) (example, Giwano Series). A special group of soils is found along the border of Lake Chad (Land System Ve3). These soils contain remnants of the aquatic and semi-aquatic vegetation and they are rich in organic matter; they are classified and mapped as Organic Hydromorphic Soils (Yo).

CORRELATION WITH SOILS OF NEIGHBOURING COUNTRIES

The soil classification system used in this report is based on that of Aubert (1965) in order to facilitate correlation with neighbouring countries. A soil map of the eastern part of Niger, at a scale of 1:500 000, was published by Bocquier and Gavaud (1964) and a soil map of Eastern Cameroon, at a scale of 1:1 000 000, by Martin and Segalen (1966).

In general the correlation of soil boundaries and classification units across the inter national frontiers is good. There are however some small discrepancies, which are caused by differences in interpretation of the classification system, different ways of representing soil complexes and differences in the amount of information available. In Niger the dune soils are regarded as transitional (intergrade) between Weakly Developed Soils of deposition and either Non- or Weakly Leached Ferruginous Tropical Soils or Semi-arid Brown Soils. In Nigeria the dune soils with lamellae formed under a rainfall higher than 500 mm (20 in) are mapped as Ferruginous Tropical Soils and not as intergrades. On both sides of the frontier Halomorphic Soils are included in the dunefields, but in Niger more detail is shown and mention is made of soils with a (sulphate) salt crust. Some alluvial areas are classified as complexes of Weakly Developed Soils, Halomorphic Soils and Vertisols. The cartographic representation of this complex is different on either side of the frontier: in Niger all 3 components are indicated, but in Nigeria only the 2 most important categories are shown.

In Cameroon, Martin and Segalen map Halomorphic Soils with Vertisols to the south of Lake Chad, but Halomorphic Soils have not been observed in the corresponding portion of Nigeria. Further south the map of Cameroon shows Vertisols, while the adjacent area in Nigeria is mapped as the vertic sub-group of the Hydromorphic Soils. The soils crack deeply during the dry season and have a strong prismatic structure, but the characteristic properties of slickensides or gilgai are missing. These soils cannot therefore, in our opinion, be clas sified as Vertisols. In Cameroon, the Mandara hills have been divided into areas with mostly Raw Mineral Soils and areas with mostly Weakly Developed Soils of erosion. Such a division has not been attempted in Nigeria. The red tropical soils reported just east of the border near Mubi (Martin et al., 1966) have not been found in Nigeria. In the above paragraphs only the differences have been emphasised and explained. If, how ever, the maps of the 3 territories are compared there is a very good agreement.

CORRELATION WITH OTHER SOIL CLASSIFICATION SYSTEMS Although the French classification system is the most widely used in West Africa, it is desirable to attempt to correlate the soils of North East Nigeria with some other important and widely used classification systems. These are the systems of the United States Department of Agriculture and the system designed for the World Soil Map (Dudal, 1968; 1969).

116 The American system was first published in its 7th Approximation (USDA Soil Survey Staff, 1960), while a revision was distributed in 1967 (USDA Soil Survey Staff, 1967). The 7th Approximation introduced an almost completely new set of names for the great soil groups and also introduced a number of diagnostic horizons. A disadvantage of the system is that the definitions are often complicated and difficult to apply to tropical conditions. The system for the World Soil Map (referred to as the World system) uses many of the basic concepts of the American system, but the descriptions and definitions are very much simpler. The supplement to the 7th Approximation introduced soil temperature and soil moisture as distinguishing characteristics at a high level of the classification. However, in recon naissance surveys in the developing countries it is almost impossible to obtain measurements of these factors. In the present report some soils have arbitrarily been placed in the Ustic or Tropic subdivisions wherever this was relevant. An Ustic soil climate has limited moisture but this is available during the optimum growing season. The soil is dry for more than 90 cumulative days, but moist for 180 cumulative or 90 consecutive days. In a tropic soil climate the mean soil temperatures are 8°C (47°F) or more, and there is less than 5°C (9°F) difference between mean summer and winter soil temperatures.

In the following paragraphs a correlation of the different classification systems is attempted for the soils of the area under review. This correlation is done by checking the definitions of the various systems against the field and laboratory data of the soils rather than by comparison of the different definitions.

Weakly Developed Soils of erosion are limited in depth to 30 cm (12 in) by hard rock. They can be closely correlated with the Lithosols of the World system, which puts the depth limi tation at 25 cm (10 in). Most of these soils will belong to the Eutric group which has a pH of 5.5 or more. In the American system the shallow soils are not separated at a high level; lithic sub-groups are established for soils with hard rock at a depth of 50 cm (20 in) or less. Weakly Developed Soils of deposition may be alluvial or aeolian in origin. The sandy allu vial soils can be compared with the Eutric Fluvisols of the World map. In the American system they would probably be classified asAquicor Typic Ustipsamments and Ustifluvents. They would be Psamments if their texture were coarser than loamy fine sand, and Fluvents if the texture were loamy fine sand or finer.

The aeolian dune soils have little or no profile development. In the French classification they are regarded as Weakly Developed Soils of deposition, transitional to Semi-arid Brown Soils, or, if they have lamellae, as Non- or Weakly Leached Ferruginous Tropical Soils. In the World system the first can be correlated with the Eutric Rhegosols and the latter either with the Eutric Rhegosols or with the Laminic Arenosols. In the American system the first would be classified as Typic Torripsamments or Typic Ustipsamments, depending on whether they were moist for less or more than 90 consecutive days. The soils with lamellae would be classified as Alfic Ustipsamments.

The correlation of the Vertisols is relatively simple as the 3 systems all use the same ter minology at the highest level. In the original version of the American classification the Vertisols were subdivided into Aquerts and Usterts on the basis of colour and mottling. This was followed by both the French and the World systems. The Vertisols of lithomorphic origin can therefore largely be correlated with the Chromic Vertisols and the topomorphic Vertisols with the Pellic Vertisols of the World system. In the American system however climatic factors once again have been introduced at high level and the term Aquert has been abolished. The 2 categories can now be correlated with the Chromusterts and the Pellusterts.

The Semi-arid Brown Soils are not very extensive and information about them is limited. They have been tentatively correlated with the Calcaric Cambisols of the World system and with the Typic Ustropepts of the American system. The Eutrophic Brown Soils are characterised by a well structured surface layer which is rich, in organic matter. This layer fulfils the requirements laid down in the American system for the 'mollic epipedon' and the soil can therefore be classified as a Mollisol. At group level the classification is Haplustoll: shallow stony soils can be correlated with the Lithic Haplustoll, while the others are Udic Haplustolls, or when they have vertic properties, Udertic Haplustolls. In the World system the surface layer would be called a 'melanic A horizon' and the soil can be correlated with the Haplic Phaeozems.

For the correlation of the Ferruginous Tropical Soils the base saturation and the presence of a textural B horizon are important criteria. The soils with a textural B horizon and a base saturation of more than 35 per cent can generally be correlated with the Alfisols of the

117 American system and the Luvisols of the World system. They would be correlated with Ultisols and Acrisols, if the base saturation was less than 35 per cent. In the area under review this is not normally the case.

Most of the Leached Ferruginous Tropical Soils of the area can be correlated with the Ustalf sub-order of the American system. At group and sub-group level the soils with many concre tions or with concretionary ironpans are equivalent to the Plinthustalfs. The soils with few or no iron concretions are comparable to the Haplustalfs. Those developed on Basement Com plex or on Cretaceous sandstone are Typic or Udic Haplustalfs if the base saturation of the B horizon is more than 75 per cent and Ultic Haplustalfs if the base saturation is less than 75 per cent. Most of the ordinary Leached Ferruginous Tropical Soils are not sufficiently mottled to place them in the sub-group of the Aquic Haplustalfs. The Hydromorphic sub-group of the Leached Ferruginous Tropical Soils can almost certainly be correlated with the Typic or sometimes with the Vertic Tropaqualfs.

For the World system the concretionary Leached Ferruginous Tropical Soils can be correlated with the Plinthic Luvisols and most of the ordinary Leached Ferruginous Tropical Soils with the Orthic Luvisols. The hydromorphic sub-group would be largely equivalent to the Gleyic Luvisols, but some of them may be regarded as at least transitional to the Ochric Planosols. In most cases the contrast between the eluvial and illuvial horizons is not sufficient.

The classification of the Leached Ferruginous Tropical Soils on poor material, as found over the Kerri Kerri Sandstone, forms a special case. It has already been stated that these soils have undergone different soil-forming processes in the past, which may have caused the forma tion of very thick textural B horizons. They can be correlated with the Oxic Paleustalfs of the American system. The prefix pale (o) indicates their old age, while the sub-group name oxic indicates the transition to the Oxisols, which are the American equivalent of the Ferrallitic Soils. In the World system they can be correlated with the new unit of the Nitosols, which are defined as having a deep argillic (= textural) B horizon, low clay activity and diffuse upper and lower boundaries. As the base saturation is generally below 50 per cent, they belong to the Dystric group of Nitosols. The correlation of the Non-Leached Ferruginous Tropical Soils has already been discussed together with the Weakly Developed Soils. The soils which are transitional between Non- Leached and Leached are regarded as soils in which the soil-forming processes are not far advanced. They have a B horizon which differs sufficiently in colour and structure from the parent material to call it a 'cambic horizon' , but there is no or little accumulation of clay. These soils can be correlated with the Typic Ustropepts of the American system and with the Eutric Cambisols of the World system.

The Halomorphic Soils are divided into leached and non-leached sub-orders. The Leached Halomorphic Soils have a textural B horizon which has an exchangeable sodium percentage of more than 10 per cent. The American nomenclature requires at least 15 per cent exchangeable sodium before such an horizon can be called natric, but some authorities consider this limit to be too high. Most of the Leached Halomorphic Soils could be correlated with the Natrustalfs of the American system and with the Ochric Solonetz of the World system. It is noteworthy that the main diagnostic feature in the American system is the textural B horizon, while in the World system and the French classification the sodium hazard is considered more important.

The Non-Leached Halomorphic Soils can probably be correlated with the Halaquepts of the American system and with the Gleyic Solenetz of the World system. Many of the ordinary Hydromorphic Soils are found in alluvial areas; they can easily be cor related with the Eutric Fluvisols of the World system. In the American system they can be correlated with the Fluventic Tropaquepts, although some may belong to the Vertic Tropaquepts. The Organic Hydromorphic Soils of the shores of Lake Chad could be classified as Humic Gleysols in the World system and as Histic Tropaquepts in the American system.

The Vertic sub-group of the Hydromorphic Soils is most similar to the Vertic Cambisols of the World system and the Vertic Tropaquepts of the American system.

These correlations are summarised in Table 13.

118 TABLE 13 Correlation of soil classification systems

French System World Map System American System

Weakly Developed Soils

of erosion Lithosols Lithic sub-groups

of deposition (alluvial) Eutric Fluvisols Aquic ) Usti. ( fluvents Typic ) ( psamments

transitional to Semi-arid Eutric Rhegosols _ . ( Torri- ) Brown Soils (aeolian) Typic ) usti- ) Psamments

Vertisols

topomorphic Pellic Vertisols Pellusterts

lithomorph Chromic Vertisols Chromusterts

Semi-arid Brown Soils Calcaric Cambisols Typic Ustropepts

Eutrophic Brown Soils Haplic Phaeozems Udic ) Lithic ) Haplustolls Vertic )

Ferruginous Tropical Soils

Non-Leached ( Laminlc Arenosols Alfic Ustipsamments ( Eutric Rhegosols

Non-Leached - Leached Eutric Cambisols Typic Ustropepts

Leached, nonrconcretionary Orthic Luvisols Ustic, Typic, Udic Haplustalfs

Leached, on poor material Dystric Nitosols Oxic Paleustalfs

Leached, concretionary Plinthic Luvisols Plinthustalfs

Leached, hydromorphic Gleyic Luvisols Typic or Vertic Tropaqualfs

Halomorphic Soils

Leached Ochric Solonetz Natrustalfs

Non-Leached Gleyic Solonetz Halaquepts

Hydromorphic Soils Normal Eutric Fluvisols Fluventic Tropaquepts Organic Humic Gleysols Histic Tropaquepts Vertic Vertic Cambisols Vertic Tropaquepts

119 -'•IE' -

PLATE 1/9 Near Gulumba. Termitaria on heavy soils in Land System Vil, the Yaribi Delta. March 1967.

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.-tut*? ^t —*^\. ,— #_'-*-. ; - • * I .* rlHka^^A-.

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^Js-j£**Z?f'*"~ ^-;'^^^^B£^c^^ ^f^ "^V^**» v •-A

PLATE 1/10 Soil erosion at the western foot of the Biu Plateau resulting from intensive utilisa tion of Ferruginous Tropical Soils derived from rocks of the Basement Complex. 120 VEGETATION by P N de Leeuw and P Tuley

PREAMBLE The relationship of the West African vegetation to the main east-west orientated eco-climate zones has been widely reported (Chevalier, 1900; Keay, 1953) and such terms as Guinea, Sudan and Sahel Zones, or their French equivalents, figure largely in environmental descriptions. Often, there is confusion as to whether the terminology is being applied to vegetation, to climate or to some broader geographical concept. It is perhaps in the last sense that the terms should be used and an attempt has therefore been made to classify the vegetation of the project area in terms of recognisable plant communities. The primarily herbaceous communities, the Aristida/Andropogon and the Sorghum grasslands and the herbaceous communi ties (17 in all) associated with the woody communities, are described and mapped separately in Volume 4. This has been done to keep together all aspects of rangeland ecology and management in the same volume. Those dealt with here are therefore the arboreal communities.

Despite the multivariant nature of the environmental influences associated with the differing plant communities, a basic understanding of the vegetation types and their distribution in the project area can be obtained from consideration of only three prime environmental factors, climatic, edaphic and anthropic.

THE RELATIONSHIP WITH CLIMATE A close relationship exists between the zones described in the section on climate and the non-hydromorphic vegetation. In the north, where the mean annual rainfall (m.a.r.) falls between 250 mm (10 in) and 500 mm (20 in), lies the belt of acacia-dominated Tree and Shrub Savanna and its anthropic derivatives. The central sector of the project area witha m.a.r. falling between 1 000 mm (39 in) and 500 mm (20 in) carries a belt of woodlands and anthropic derivatives dominated by species of the family Combretaceae. Annual rainfall much in excess of 1 000 mm (39 in) is restricted in the project area but, as this level is approached and exceeded, the combretaceous woodlands are replaced by ones dominated by species of the family Leguminosae. The characteristics of the so-called Sub-Sudan Zone have been discussed in the section on climate. This complex climatic pattern occurring at the critical rainfall level between 900 mm (35 in) and 1 000 mm (39 in) is reflected in the nature of the vegetation of the area. A high proportion of 'intergrade communities' are to be found, intermediate in species composition between typical Sudan and Northern Guinea Zone communities. There are also rapid changes in the vegetation pattern and localised pockets of plant communities atypical of the surrounding vegetation.

The effects of altitude in the project area appear to be largely confined to the influences on rainfall pattern. Despite the gross *blanketing' rain shadow effect of the Jos/Bauchi Plateau, subsequent orographic influences are still effective enough to produce secondary rain shadows and, particularly in the south, elevated areas tend to carry a 'wetter' vegeta tion on their westward/northwestward windward slopes. Although parts of the Mandara range rise to 1 200 m (4 000 ft), the effects on vegetation do not appear to be as marked as those found on elevated areas to the south and west. However, the highlands have typically been subjected to a high level of utilisation which may mask the altitude effect, and collections of 'upland' species are recorded in the literature (Letouzey, 1968). The Zummo Mountains appear to be something of an exception and probably merit further botanical investigation.

THE RELATIONSHIP WITH SOILS The experience of Ramsey and de Leeuw (1966) is typical of the survey area as a whole, in that the overriding edaphic factor is soil-water. With the exception of the effects of salinity discussed below, in virtually every case investigated the distribution of the vegetation can be equated with soil/water relationships. In certain areas, where for example

121 direct impedence to root growth by concretionary ironstone or subsurface rock occurs, there may be doubt as to which effect predominates but, by and large, the concept holds true throughout the survey area. On freely draining soils the relationships with rainfall are readily identifiable while the communities on heavy clays and similar soils span a wider climatic range. Perennially wet communities are extremely similar throughout the project area. In any climatic grouping, three edapho-nodal communities can usually be identified, associated with skeletal stony soils:: sands, sandy loams, and clay soils. Intergrade communities can usually be typed in terms of intermediate properties of the soils.

Hill and steep-slope vegetation often presents problems in description and the application of an appropriate mapping unit. Usually such areas are not intensively investigated and are often mapped as carrying some form of thin soil' community. In many locations this is a valid classification but it by no means always holds true. The term 'Inselberg Community' has been coined to describe the situation where large expanses of exposed, sometimes smooth, rock occur. Typically in such circumstances a low annual or perennial 'cushion' community is found on the rock faces, while the deep and often fertile soils of the interrock crevices and pockets carry well developed woodland, sometimes with elements of the riparian communities found in the area. Tall and lush grasses are also typical of such sites. Thin soil' communities may also occur in close proximity to the better developed rock sites.

In the survey area, salinity is invariably associated with the heavier soils. A large proportion of the clay soils has at least some tendency towards halomorphism, the extent of which is reflected in the vegetation, or in extreme cases the near absence of vegetation.

THE RELATIONSHIP WITH MAN Throughout much of the area, the form of the vegetation is largely a reflection of the impact of man and his livestock. The resultant 'secondary* communities are extremely variable both in form and ecological status. They can vary from apparently stable disclimaxes to serai communities, the nature of which depends on the point in time of the observations, in a cycle of regeneration from utilisation to full regrowth. In consequence, it is often difficult to find a satisfactory classification for them but, in view of their importance, an effort must be made to present as clear a botanical and spatial picture of them as possible. Farming and stock-rearing activities in the area are described in Volume 4 and for the purpose of this section the results of the whole range of activity, burning, cultivating, grazing, trampling and so on, are considered together. The descriptive and mapping units selected fall into two main categories.

1. Parklands. These are typically areas of intensive and/or long-standing cultivation. The cover is largely fallow regrowth of herbaceous species with a few highly persistent shrubs. Scattered mature trees, usually of economic value, give this unit its characteristic appearance.

2. Tree and Shrub/Shrub Savannas. These are typically derivatives of a lower level of impact, such as shifting and cyclic cultivation and open-range grazing.

Cultivation in the broadest sense can be equated with desiccation and heavily cultivated areas in a wetter regime often have the appearance of lightly cultivated areas in a drier one. This feature often presents problems, particularly in the Sub-Sudan areas where it is often not possible to determine if the presence of Sudan-like conditions is due to long standing cultivation or to climate. The matter is further complicated in that drier areas tend to have fewer human and animal disease problems and hence tend to attract the cultivator and pastoralist.

CLASSIFICATION OF PHYSIOGNOMIC TYPES The physiognomic terminology employed in this report is essentially that laid down at the Yangambi Meeting (CCTA/CSA, 1956). Despite subsequent objections from East African workers (Pratt et al., 1966), the terms are in such common usage and are so widely recognised in West Africa that their retention is advisable until some universally accepted scheme is available.

122 METHODOLOGY The data upon which the proposed plant communities occurring in the project area are based have been generated from three main sources. First, records of presence and abundance of species largely collected in the course of the surveys described in the section on soils, some of which data have been subjected to statistical analysis (Ramsay and de Leeuw, 1965). Second, vegetation records and field notes collected by the authors. Third, interpretation and extrapolation of published data applicable to the project area. A list of the last is available in Posnett et al. (1971).

CLASSIFICATION OF PLANT COMMUNITIES The study of phytosociology, defined by Lambert and Dale (1964) as 'the study of plants as gregarious entities', has led to differing systems of recording, describing and classifying plant communities. These differences are understandable in view of the diversity of both the vegetation being observed and the objectives of the observers. Without entering into the merits and disadvantages of the various approaches to vegetation study it appears clear that the concept of 'associated species', namely, a near-constant grouping of species that tends to occur under the same environmental circumstance, is fundamental to all. In more recent times the emphasis on delineating well defined and often 'rigid' plant communities has diminished, even in such an orthodox school as that of Braun-Blanquet, partly due to many vegetation surveys being conducted in regions where the knowledge of the local flora was inadequate. The concept of faithful and characteristic species is best adopted for distinguishing plant communities in areas where the local flora is well known and where there is an adequate fund of related environmental data. This view was recently expressed by Doing (1970). 'It should be admitted openly that new vegetation units must be primarily based on other criteria than faithful and differential species and that a direct link between species and vegetation types generally does not exist. An intermediate category between both abstract units: the sociological species group, seems necessary'. Zonneveld (1970) coined the term 'ecological group of species' as a group of plant taxa sharing the same habitat in a greater degree than expected if the taxa were randomly distributed. At the same time the group should have a statistical correlation with a measured or estimated environmental factor. The term 'sociological group' is proposed when no such statistical correlation has been established.

The plant communities described here can be defined as plant associations in the generally accepted sense or a combination of 'ecological groups of species' and 'sociological groups' as defined by Zonneveld. In addition, the descriptions provided are largely 'nodal' in character in the sense of Poore (1955). The format is aimed at providing a clear definition of the typical land facet/climate/plant community relationship to allow ease of presentation in the land system descriptions in Volume 3. These nodal groups of species can be considered as assemblies of associated species which are adapted to a specific range of climate, edaphic and anthropic factors. They also serve as concise mapping units for the accompanying vegetation map (Map 4). However, within the survey area, intermediate environmental circum stance gives rise to 'intergrade plant communities' intermediate in character between the main nodal formations. Where such communities are spatially important, they are also described and mapped.

It should be noted that even the major nodal units are not all of the same ecological status. For example, the leguminous woodlands of the higher rainfall areas and the Acacia Tree Savannas of the far north can probably be considered as approaching a climax vegetation while the great belt of combretaceous woodland across the centre of the area is probably a disclimax.

In Tables 14 to 25 an attempt has been made to design a visual presentation of the species composition of the major plant communities of the project area. In Figure 15, the communities are spatially arranged, in terms of their environmental relationships. In general terms the circles represent near 'natural' units while the squares are anthropic derivatives. In the tables the communities are arranged as closely as possible to the sequence shown in Figure 15.

123 Environmental relationships of the major woody plant communities Figure 15

Climatic Factors SAHEL SUDAN. SUB-SUDAN NORTHERN GUINEA Edaphic Factors

LITHOSOLS ® © © © 0 26 25 DEEP, FREELY *—' DRAINING SOILS 33 ? £® 24 23 12 4 ^—=. 7 ^=5 5 34 20, IMPERFECTLY DRAINED SOILS ^ 29 (HYDROMORPHIC) (§>

IMPERFECTLY DRAINED SOILS -?- 30 © (VERTIC) © ©^HÏ^Kjo) ^ {jT|

IMPERFECTLY DRAINED SOILS 28^29 (HALOMORPHIC)

Anthropic links

RIPARIAN/SWAMP SOILS Savanna woodlands O & tree savannas

Shrub savannas, D fallows & parklands

D.O.S. 3099 O Alluvial complexes - woody vegetation Figure 16 Schematic relationship of the major plant communities

31. 32 & 33 36b 36b 36b 27,28 & 29 36a & 29

^j>^?ör A ?yy _T^f_

Dunes and remnant sand plain Grass swamp with Main channel Clay plain Sand islands wet sand islands and levees

Northern Alluvial Complex

37a 37d 37d 37b 37c 10. 16, 17.18.27 & 28

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Flood plain Rock outcrops Main channel Wooded Raised areas with Clay flat and denuded banks levee high water table

Southern Alluvial Complex

38d 38b 38a 38c

mlJ1! »wys/wtfw>M('j!r

Incised tributary Stream Main channel Grass/sedge swamp Main channel Stream bank Upland bank and "Fig Island"

Deji/Gaji Complex

D.O.S. 3099 R

125 The Species List *

The species list has been made as complete and representative as possible of the woody plant life in the project area. It has however proved necessary, due to limitations of space, to omit certain species that the authors would otherwise have liked to include. Examples of these are' Cochlospermum spp., so very typical of lithosplic sites; Asparagus spp., Adenium honghel and Euphorbia unispina, sometimes very prominent locally on heavy clays, particularly in the south of the project area; and in the rich flora (unique to the area) of the Deji/Gaji Complex only a representative sample of species is shown in the list.

An attempt has also been made to arrange the species in environmentally related groupings. With some species this is relatively easy to do but others could be placed in two or more categories. Where this occurs, as for example Khaya senega lens is which could just as readily be placed under riparian species as farm and fallow ones, the species has to be arbitrarily placed in one category only.

In the tables four communities can be accommodated on each page. Within each there are four 'abundance classes' and a diagonal line represents the presence of a species.

Alluvial Complexes

In order to obtain a reasonable mapping unit, all communities associated with the river systems have been grouped into three complexes. The component communities of the complexes are however defined in the following tables and their generalised relationships are shown in Figure 16. The vegetation associated with the tributaries entering the Gongola at its northern extremity is shown in Map 4 as being of the Southern Alluvial Complex. It does however have many unique features and is probably best considered as an intermediate with the Deji/Gaji Complex.

* Note on spelling. The spellings of the genera (e.g. Ziziphus and Annona) used here were derived from The Flora of West Tropical Africa by J. Hutchinson and J. M. Dalziel (Second ed.) 1963, London: Crown Agents and not from the Index Kewensis.

126 v* :u pf-4 fpcf

PLATE 1/11 Typical Anogeissus Woodland south of Damboa. March 1967.

PLATE 1/12 Lannea humilis. A typical gregarious clump showing the low contorted habit. 127 1 APRORMOSIA/DETARIUM WOODLAND/TREE SAVANNA - BüRKEA VARIANT Physiognomy Open to dense savanna woodland, standing 10-15 m (33-50 ft) high, with usually a well developed understorey of shrubs.

Dominant Characterised by the presence of such typical Northern Guinea species as Afrormosia, floristics Detarium, Burkea, Tetrapleura, Cuasonia, Afzelia, Isoberlinia, Swartzia, Adenodolichos, Hymenocardia and Daniel Iia. Environmental The characteristic woodland in the project area where Northern Guinea or near Northern relationships Guinea conditions occur on free-draining to lithosolic sites. It probably reaches maximum development in parts of the Wawa Bush (Land Systems Illbl and IIIb2) and in some parts of the Gombi Plain (Land System Ibl).

Species list Based on a typical 0.2 ha (0.5 ac) plot in the Wawa Bush (Table 14. Column 1).

2 APRORMOSIA/DETARIUM WOODLAND/TREE SAVANNA - DETARIUM VARIANT

Physiognomy Similar to (1), usually somewhat lower in height.

Dominant Similar to (1), but with Detarium more predominant. Crossopteryx is a conspicuous floristics shrub. Environmental Of similar climatic distribution to (l), but more typical of stony sites and drier relationships conditions generally.

Species list Based on traverse in the Song area of Land System Ic3 (Table 14, Column 2).

3 APRORMOSIA/DETARIUM WOODLAND/TREE SAVANNA - ISOBERLINIA VARIANT Physiognomy Similar to (1), the canopy typically more closed and the stand denser.

Dominant Similar to (1), but with the conspicuous presence of Isoberlinia spp. often in pure floristics gregarious stands. The species list records the presence of /. doka but a proportion of this is I. dalzielii wrongly identified. On the pediments of the Mandara range (Land System Ic2) occurs a variant Isoberlinia/Anogeiasus Woodland. It contains many elements of the Terminalia/Combretum Shrubland (Communities 4 and 5) and significant numbers of emergent tree species usually associated with farmland such as Butyrospermum, Parkia, Ficus spp., and Tamarindus. It would appear to differ from the more typical type due to past anthropic influences. The status of this community will be reviewed in the light of investigations at present in train in the central Northern Guinea areas of Nigeria. At the present state of our knowledge 'Isoberlinia Woodland' does not appear to occur in our area with the possible exception of the Longuda Upland (Land System IVa2). Environmental Of similar climatic distribution to (l). Although associated with rocky and other relationships lithosolic sites, this community is primarily distributed on local colluvial soils in these areas with good profile depth and improved water relations due to the impedence of percolation by the underlying material. Species list Traverse from Uba to Mubi showing anthropic influences (Table 14, Column 3). Traverse near Little Gombi showing anthropic influences (Table 14, Column 4).

128 SPECIES LIST Table 14

Community Number Community Number

Common trees & shrubs Common species on llthosols HAR>90Cfln (30 Inj

Balanites aegyptiaca Acacia dudgeonl . Sterculla setlgera. Burkea afrlcana . Anogelssus leloearpus Acacia hock 11 . . Lannea schlmperl Afzella afrlcana . Bombax costatum Isoberllnia doka . Prosopls afrlcana 1. dalzlelll . Pterocarpus erlnaceous Monotes kerst lngll . Sclerocarya blrrea Haematostaphls barterl . Entada afrlcana Combretum molie Species on heavy solfrg C. ghasalense _ C. glutlnosum _ Feretla apondanthera Gulera senegalensls Combretum aculeatum .. Zlziphus maurltlana Securlnega vlrosa PUlostlgma retlculatum Capparls spp. Cassia singueana Acacia ataxacantha^_ Annona senegalensls Dlchrostachys glomerata Grewla mollis _ Grewla flavescens Gardenia spp. _ G, laslodlscus . Xlmenla amerlcana Clssus quadrangularIs . Maytenus senegalensls Pseudocedrela kotschyl , Commiphora afrlcana Nauclea latlfolla C. pedunculata Lannea humllls Zlslphus mueronata Acacia seyal . A. pOlyacantha/campylacantha Common trees & shrubs MAR > 750 mm (30 In) A. slebenana MItragyna inermls Steganotaenla arallacea n Stereospermura kunthlanum Trees of farmland and fallow Securldaca longepedunculata Kezalobus monopetalus Adansonla dlgltata. Termlnalla brownll. Acacia alb Ida Hannoa undulata A. arablca var. adansonll Heerla Ins Ignis Tamarlndus lndlca Trlchllla roka Dlospyros mesplllformls Vitex slmpllclfolla Adenodollchos panlculatus Flcus spp. . Swartzla madagascarlensls Borassus aethloplcura Hymenocardla aclda— Butyrospermum paradoxum Pteleopsls suberosa Vltex donlana - Grewla vlllosa Park la clappertonlana Danlellla ollverl Pavetta sp. -— Khaya senegalensls. Ochna schwelnfurthiana cussonla barterl Riverain species Amblygonocarpus andongensls Parlnarl curatelllfolli P. polyandra Tetracers alnlfolla — Syzyglum gulneense— — Combretum blnderlanum Pteleopsls habeensls — C. hypopilinuTi Termlnalla macroptera — C. nigricans var. elllotll • Alchornea cordlfolla — Termlnalla avicennlold'es Kacaranga schwelnfurthll T, laxlflora S— —- Mimosa plgra — — Plllostlgma thonnlngll MUlettla thonnlngll — Irvlngla anlthll — locally common or rare trees and shrubs -Ttebergla senegalensls — MAR 500- 1 OOP mm (20 - iiO In) Paulllnla plnnata — Malacantha alnlfolla — Dalbergla melanoxylon MItragyna clllata — Cassia sleberlana Klgella afrlcana —. — Cassia arereh Raphla sudanlca — — Randla nllotica Elaels gulneensls — AlblEla chevallerl Pandanus candelabrum — Lonchocarpus sp. — Garclnla oval1 folia — Maerua angolensls Salix ledermann11 — Boscla sallclfolla Celtls lntegrlfolla — Common trees & shrubs MAR < 500 ran (20 lp) Rare species Acacia raddlana A. Senegal Croton zambeslcus _ A. nllotica var. nllotica Gardenia sokotensls _ Cordla rothll Acacia hebecladoldes _ Salvadora perslca Holarrhena florlbunda _ Leptadenla pyrotechnlca— Uvarla chamae — Maerua crass 1 folia Ormocarpum sp. _ Bauhlnla rufescens — Erythrlna senegalenls ._ Commiphora quadrlclncta Opllla celtldlfolla _ Capparls corymbosa— _ Calotropls procera Cadaba farlnosa Carlssa edulls _ Hypheane thebalca Fadogla spp. —. — Allophylus afrlcanus _ Common species on llthosols Antldesma venosum ,— _ Psorospermum febrlfugum_ Termlnalla glaucescens _ Boswellla dalzlelll Leptadenla arborea — Detarlum mlcrocarpum Afrormosla laxlflora Strychnos splnosa — . Addendum S. lnnocua Boscla senegalensls. Brldella ferruglnea Tecrapleura sp. _*_ Crossopteryx febrlruga Securlnega »Irosa . •I Lannea sp.

129 4 TERMINALIA spp./COMBRETUM spp. SHRUB SAVANNA

Physiognomy A low shrubland or fallow regrowth. There are scattered emergent trees.

Dominant Typically Terminalia avicennioides and T. laxiflora CO-dominant with floristics Combretum glutinosum, C. binderianum, C. ghasalense and sometimes C. hypopilinum. In the southeast sector 7". brownii is a common record while in the southwest, particularly in the wetter areas about the Lamurde anticline, Pteliopaia auberosa is a conspicuous constituent of the shrubland. Emergent trees are those typical of Community 1 together with 'economic* species typical of farmland such as Parkia, Tamarindus , Vitex doniana, Ficus spp. and Butyroapermum. in cultivated areas in the Wawa Bush, Terminalia spp. are common in the regrowth but, as the Combretum spp. so predominate, this intermediate area has been mapped as Combretum shrub Savanna (Community 12). Environmental An anthropic derivative of Community 1, occurring under Northern Guinea or near relationships Northern Guinea conditions.

Species list Based on traverses in the eastern Basement Land Province, the Gombi Plain and the Zomba Plain, Land Systems Ibl and Ib6. (Table 15, Column 1). Based on a traverse in the Lamurde Pediplain, Land System IIb2 (Table 15, Column 2).

5 TERMINALIA spp. /COMBRETUM spp. SHRUB SAVANNA - ISOBERLINIA VARIANT Physiognomy A low shrubland or fallow regrowth. There are scattered emergent trees.

Dominant Similar to (4) but with a conspicuous regrowth of Iaoberlinia spp. sometimes floristics forming uniform, nearly pure stands. Environmental This community is probably best considered as an anthropic derivative of relationships Community 3, occurring under similar climatic and edaphic conditions. It is to be found in the eastern Basement Land Province and on the Biu Upland, Land System IVal. Species list Traverse from Uba to Mubi (Table 15, Column 3). Based on records taken in the Little Gombi and Biu areas (Table 15, Column 4).

130 SPECIES LIST Tabl 15

Community Number Community Number

Common trees & shrubs Comnon species on llthosols HAR>90Omn (30 In)

Balanites aegyptlaca . Acacia dudgeonl . sterculla setlgera . Burkea afrlcana Anogelssus lelocarpus . Acacia hockII Lannea schlmperl — . Afzelta afrlcana Bombax costatum — . Isoberllnla doka -— Prosopls afrlcana . I. dalzlelll Pterocarpus erlnaceous . Monotes kerstlngll Scleroearya blrrea . Haematostaphls barterl —- Entada afrlcana .— — . Combretum molle — - Species on heavy soils C, ghasalense — . • C. glutlnosum — . Feretla apondanthera Gulera senegalensls — . Combretum aculeatum . Zlzlphus maurltlana . Securlnega vlrosa Plllostlgma retlculatum . Capparls spp. Cassia slngueana . Acacia ataxacantha Annona senegalensls . Dlchrostachys glomerata Grewla mollis —. — . Grewla flavoscens Gardenia spp. - G. las lod 1 scus Xlmenla americana - Clssus quadrangular Is _ Maytenus senegalensls . Pseudocedrela kotschyl S Commiphora afrlcana — Nauclea latlfolla C. pedunculata — Lannea humllls s Zlzlphus tnucronata .— — . Acacia seyal A. pOlyacantha/campylacantha s: Common trees & shrubs MAR > 750 run (30 In) A. sleberiana Mltragyna lnermls s Steganotaenla arallacea . B Stereospermum kunthlanum . . Trees of farmland and fallow Securldaca longepedunculata Hexalobus monopetalus . Adansonla dlgltata Termlnalla brownll Acacia alb Ida . Hannoa undulata —. - A. arablca var. adansonli . _ Heerla Inslgnls Tamarlndus Indies Trlchllla roka — — Olospyros mesplllformls Vltex slmpllclfolla Flcus spp. Adenodollchos panlculatus — . Borassus aethioplcum Swartzla madagascarlensls . Butyrospermum paradoxum Hymenocardla aclda — . Vltex doniana -— Pteleopsls suberosa — Park la clappertoniana GrewJa vlllosa — — — . Danlellla ollveri Pavetta sp. — Khaya senegalensls — — Ochna schweinfurthlana —— Cussonla barterl Riverain species Amblygonocarpus andongensls —- . Parlnarl curatelllfolla Tetracers alnlfolla — — P. polyandra . Syzyglum guineense— — Combretum blnderlanum Pteleopsls habeensls — — C, hypopiUntil) —- • Termlnalla macroptera — C, nigricans var. elllotll — Alchornea cord 1 folia — Termlnalla avlcennlQldes Macaranga schwelnfurthll — T. laxlflora — — — Mimosa plgra — Plllostlgma thonnlngll Mlllettia thonnlngll Irvlngia smlthll — locally common or rare trees and shrubs .^ebergla senegalensls MAR 500- 1 OOP mm (20 - /jO In) Paulllnla pinnata Malacantha alnlfolla Dalbergla melanoxylon Mltragyna clllata — — Cassia sleberlana Klgella afrlcana —— — cassia arereh Raphla sudanlca — •— — Randla nllotica . Elaels guineensls —- AlbIzla chevallerl . Pandanus candelabrum — Lonchocarpus sp. — Garclnla ovallfolla rlaerua angolensls — — Salix ledermannll — — Boscla sallclfolla ft Celtls integrlfolla Common trees & shrubs MAR < SOP mm (20 In) Rare species Acacia raddlana A, Senegal . Croton zambeslcus — — A, nllotica var. nllotica . Gardenia sokotensls — — cordla rothll . Acacia hebecladoldes — Salvadora pers lea Holarrhena floribunda — — — Leptadenla pyrotechnlca— Uvarla chamae — •— Maerua crass I folia Ormocarpum sp. Bauhlnla rufescens - Erythrlna senegalenis Commiphora quadrlclncta Opilia celtidlfolla Calotropls procera Capparls corymbosa— — Cadaba farlnosa Carlssa edulls — Hypheane thebalca — Fadogla spp, Allophylus africanus Common species on llthosols Antldesma venosum Psorospermum febrlfugum — Termlnalla glaucescens — Boswellla dalzlelll . . Leptadenla arborea Detarlum mlcrocarpum Afrormosla laxlflora Addendum Strychnos splnosa S. lnnocua Boscla seneRalensls— — — — — — Brldella ferruglnea . Tetrapleura sp. — — — — — — s Crossopteryx febriruga Securlnega »Irosa _;_ HI Lannea sp. _• —

131 6 ACACIA HOCKII TREE AND SHRUB SAVANNA Physiognomy Low, widely spaced trees standing to 3-5 m (10- 16 ft) with scattered shrubs.

Dominant The distinctive species in this community are A. hockii, Entada and Paeudocedrela floristics in association with Combretum glutinoaum, C. ghaaalense and Ziziphua mauritiana. Environmental This community is confined in our area to basalt-derived heavy clay soils on the relationships high lava plateaux. It is rarely free of some level of anthropic impact and occurs under near to full Northern Guinea conditions. It bears some similarities to the Acacia aeyal/Pseudocedrela community described by Clayton (1955) on heavy clays in the Shendam-Bashar area immediately to the west of the project area. As also described under Community 14, there is a tendency for A. hockii to replace other Acacia spp. on soils derived from basaltic materials.

Species list Based on 0.2 ha (0.5 ac) plots and traverse records on the Biu Upland, Land System IVal (Table 16, Column 1).

7 PARKIA PARKLAND Physiognomy A low farmland fallow with scattered regrowth of persistent shrubs and occasional widely spaced trees, usually of some economic value. Dominant The herbaceous cover is described in part in Volume 4. The regrowth shrubs are floristics those typical of Communities 4, 5, and 12. Typical trees are Parkia, Vitex, Butyroapermum, Daniellia, Khaya and Ficua spp. Environmental Long-standing, usually intense cultivation in the Northern Guinea and Sub-Sudan relationships Zones. Species list None.

8 ANOGEISSUS/COMBRETUM spp. WOODLAND/TREE SAVANNA Physiognomy Variable from a low open woodland of the order of 3-6 m (10-20 ft) high to one containing a high proportion of dense, tall shrubs. Occasional taller emergent trees occur, often in localised groups. The density of erect woody stems per unit area is higher in this community than any of the other woodlands/tree savannas in the project area.

Dominant Fairly rich in species but with a clear dominance of Combretaceae. Anogeisaua floristics and Combretum nigricans var. elliotii are the typical dominants With C. glutinoaum and Terminalia spp. often co-dominant. However, this community often intergrades into Communities 1-3 and a conspicuous proportion of leguminous trees results. Environmental Widely distributed in the Sub-Sudan areas of the Gongola Valley and in the Wawa relationships Bush on free-draining sites. It is possible that this community has arisen from past anthropic influences on the Afrormoaia/Detarium woodlands to which it may be slowly reverting. It would certainly appear to occur on the climatic boundary between the leguminous woodlands of the Northern Guinea Zone and the Anogeiaaus Woodlands of the Sudan Zone. It probably is most typically seen on the very free-draining soils in the Wawa Bush.

Species list Based on 0.2 ha (0.5 ac) plots and traverses in the Wawa Bush, Land Systems Illbl and IIIb2 (Table 16, Column 2). . Based on 0.2 ha (0.5 ac) plots in the Gombe Hills, Land System IIc3 (Table 16, Column 3). Based on typical 0.2 ha (0.5 ac) plots on the sandstone plains of the Gongola Valley, Land Systems Ilbl, 2, 3 and 4 (Table 16, Column 4).

132 SPECIES LIST Table 16

Community Number 6 8 8 8 Community Number 6 8 8 8

Common trees & shrubs COTx»n SDecïes on llthosols MAR>90Cnn ^jSO In^

Um*»:. „fr-Irana ^^^TBT ^J ^^ Anarln hnrt.ll • 11 ^N TW WW Af7»lla Jifrlrana •! |\ |

I, rtalilolll J J

. pedes op heavy so 1;

Zlzlphus maurltlana — — W Pillostigma reticulatum — U- Cassla slngueana — L Annona senegalensis B Grewla mollis— — — — WL. Grpwla fl.ivoRrpns

Maytenus senegalensis — — II

Common trees & shrubs MAR > 750 mm (30 fn) • ^ I -tT - t-T TB t-Jt- --T .jr.~£-_ • • • • V1f.i»r nlmpllrlfnlln \ ^ " " " JL Swartzla madagascarlensls -- c::: _ -4-• - —jtt-T.- n •: --ff-- 1 Riverain species 1 1 1 1 1

Termlnalla avlcennloldes -— ••

Locally common or rare trees and shrubs MAR 500. 1 000 mm (20 - IjO ini DAlhprgla mplftrmxylnn 1 ...s_._ i.._i _ . -S ^:: Vs : --I - i:::3t 1 : ..::&- ::nr~ • i Common trees & shrubs MAR < 500 mm, (20 JnJ Rare species Aeada rorldlanA

flpllln «»lr.Hlffllln

p^dogf« "»PP.

Addendum

133 9 ANOGEISSUS/DETARIUM SAVANNA WOODLAND/TREE SAVANNA Phys iognomy A low woodland at full development with emergent trees standing 10-13 m (33-43 ft) high. A well developed understorey of shrubs.

Dominant This community contains many elements of Community 19, Anogeissus Woodland, and floristics can be regarded as a mosaic of this with an impoverished northern form of the Afrormosia/Detarium - Detarium variant Community. In the latter, Detarium, Crossopteryx and Strychnoa spinosa dominate with a well developed shrub stratum Of Combretum glutinosum and Guiera.

Environmental A Sub-Sudan climatic intergrade community on lithosolic sites. It covers the relationships transition on such sites from Community 2 to Community 14. Its largest extension occurs on the ironstone outcrops over Kerri Kerri Sandstone in Land Systems Illbl and 2 and on the northerly parts of the eastern Basement Land Province in Land Systems Ib2 4 and 5. Species list Based on 0.04 ha (0.1 ac) plots in Land Systems Illbl and 2. (Table 17, Column 1).

10 ACACIA SEYAL/A. POLYACANTHA SAVANNA WOODLAND/TREE SAVANNA Physiognomy Spreading trees, usually scattered but at full development sometimes forming a closed canopy. Typical height about 5 m (16 ft) with occasional taller trees standing to 8-9 m (26-30 ft).

Dominant This community is very similar to Community 17 which is described in more detail. floristics It differs in the more conspicuous proportion of A. polyacantha subsp. campylacantha and the greater prominence Of Mitragyna inermis and Entada.

Environmental Confined to the Sub-Sudan Zone in the project area. It is probably best relationships considered as a 'wetter' variant of Community 17 occurring on heavy clays under higher rainfall and also where the density of the drainage network exerts a riparian influence. It occupies sizable areas on the Giwano Plain, Land System IIa6, where it forms a mosaic with the Sorghum grassland of Community 13. Else where it usually occupies discrete low-lying areas distributed among the Anogeissus/Acacia seyal Savanna Woodlands, Community 16. Species list Based on 0.2 ha (0.5 ac) plots in the Deba Habe area of the Wagur Plains, Land System IId4 (Table 17, Column 2).

11 ACACIA DUDGEONII/COMBRETUM GLUTINOSUM TREE AND SHRUB SAVANNA Physiognomy A low shrubland with emergent trees standing to 5 m (15 ft) either scattered or in localised clumps. Dominant The species composition is similar to Community 14 with the additional presence floristics Of such typical fallow species as Pilioatigma, Entada, Maytenus and Terminalia laxiflora. Environmental An anthropic derivative of Cummunity 14, occurring in the Sub-Sudan Zone on relationships lithosolic and thin-soil sites generally. It is particularly conspicuous in the densely populated areas on rocks of the Basement Complex. Species list Based on 0.2 ha (0.5 ac) plots in the Wandali area of the Whada Plain, Land System Ia2 (Table 17, Column 3). Traverse on the Gongola Hills, Land System Ic5, near Kaltungo (Table 17, Column 4).

134 SPECIES LIST Table 17

Community Number 10 11 11 Communitv Number 10 11

Common trees & shrubs Common species on llthosols MAR>900mm (30 In)

Balanites aegyptlaca Acacia dudgeon! Sterculla setlgera Burtcea afrlcana . ,, . Anogelssus lelocarpus Acacia hock 11 ÏÏM Lannea schlmperl Afzella afrlcana £ Bombax cos tatum Isoberllnla doka Prosopls afrlcana 1. dalzlelll Pterocarpus erlnaceous rlonotes kerstlngll . Sclerocarya blrrea Haematostaphls barterl Entada afrlcana Combreturo mo lie Speeres on heavy soils C. ghasalense _ C, glutlnosum _ Feretla apondanthera Gulera senegalensls Combretum aculeatum Zlzlphus maurltiana Securlnega vlrosa Plllostlgma retlculatum Capparls spp. Cassia slngueana Acacia ataxacantha__ . . Annona senegalensls Dlchrostachys glomerata Grewla mollis _ Grewla flavescens Gardenia spp. _ G. laslodlscus t Xlraenla amerlcana CIssus quadrangular Is (laytenus senegalensls Pseudocedrela kotschyl ; Commiphora afrlcana- Haue lea lat 1 rol la C. pedunculata Lannea humllls Zlzlphus mucronata. Acacia seyal A. pOlyacantha/campylacantha Common trees & shrubs MAR > 750 mm (30 In) A. sleberiana Mltragyna Inermls Steganotaenla arallacea Stereospermum kunthlanum Trees of farmland and fallow Securldaca longepedunculata Hexalobus monopetalus . Adansonla dlgltata Terminal la brownll — Acacia alb Ida . __ Hannoa undulata A. arablca var. adansonll Heerla Ins Ignis — —. Tamarlndus indlca __ :s: Trlchllla roka — — Dlospyros mesplllformls vitex slmpllclfolla I Flcus spp. — Adenodollchos panlculatus — Borassus aethloplcum _*_ Swartzla madagascarlensls —- Butyrospermum paradorum Hymenocardla aclda — Vltex donlana — Pteleopsls suberosa —- — Parkla clappertonlana Grewla vlllosa — — — Danlellla ollverl Pavetta sp. — — — — Khaya senegalensls — — Ochna schwelnfurthlana s Cussonla barterl .— Riverain species Amblygonocarpus andongensls Parlnarl curatellirolla —- — Tetracers alnlfolla — P. polyandra - Syzyglum gulneense— — — — — Combretum blnderlanum Pteleopsls habeensls — — — C. hypopilinum Termlnalla macroptera C. nigricans var. elllotll — Alchornea cordlfolla Termlnalla avlcennloldes -— T. lax 1 flora — — Macaranga schwelnfurthll Mimosa plgra —- Plllostlgma thonnlngll — hL. Mlllettla thonnlngll Locally common or rare trees and shrubs Irvlngla smlthll .Ttebergla senegalensls — — — — MAR 500- 1 000 mm (20 - 1;0 In) Paulllnla plnnata Malacantha alnlfolla Dalbergla melanoxylon . Mltragyna clllata — — — — Cassia sleberlana — Klgella afrlcana Cassia arereh Raphla sudanlca — — Randla nllotica Elaels gu ineens Is — Alblzla chevallerl [ Pandanus candelabrum Lonchocarpus sp. — Garclnla ovallfolla — — — — Maerua angolensls — Salix ledermannll — Boscla sallelfolla — Celtls Integrlfolla — — — Common trees & shrubs MAR < 500 mm (20 in) Rare species Acacia raddlana _ A. Senegal _ Croton zambeslcus — A. nllotica var. nllotli Gardenia sokotensls — — . — u Cordlarothll _ Acacia hebecladoldes — — Salvadora perslca _ Holarrhena florlbunda — Leptadenla pyrotechntca- Uvarla chamae — —- — — Maerua crass 1 folia _ Ormocarpum sp. Bauhlnla rufescens _ Erythrlna senegalenls -— Commiphora quadrlclncta— Opllla celtldlfolla Calotropls procera _ Capparls corymbosa— —- Cadaba farlnosa _ Carlssa edulls ___ - Hypheane thebalca _ Fadogla spp. Allophylus afrlcanus Common species on llthosols Antldesma venosum .. _ Psorospermum febrlfugura Termlnalla glaucescens — Boswel11a dalzlelll Detarlum mlcrocarpura Leptadenla arborea Afrormosla laxlflora Addendum Strychnos splnosa — . S. lnnocua — . Boscla senegalensls — — — Brldella ferruglnea Tetrapleura sp. -_ — — Crossopteryx febrlruga. . Securlnega vlrosa s: •I Lannea sp.

135 12 COMBRETUM spp. SHRUB SAVANNA Physiognomy An open to dense low shrubland with occasional emergent trees. Dominant This community spans a range of shrublands dominated by species of Combretum. floristics In the Wawa Bush and on sandy soils in the southwest of the project area C. nigricans var. elliotii and to a lesser extent C. binderianum tend to dominate. To the east and north, C. glutinosum and C. ghasalense are more conspicuous. Environmental This community is best considered as a plastic anthropically derived shrubland relationships distributed largely in the Sub-Sudan Zone and the higher rainfall sector of the Sudan Zone. It forms a transition between the rernunaiia-dominated shrublands of the Northern Guinea Zone and the Guiera-dominated ones of the Sudan Zone. This transi tion is reflected in the changing proportions of associated species and such species as Terminalia laxi flora are replaced by such Sudan elements as Guiera, Annona, Cassia singueana and Ziziphus, as drier conditions prevail. Species list Based on 0.2 ha (0.5 ac) plots near Dukku in Land System Illbl (Table 18, Column 1). Based on 0.2 ha (0.5 ac) plots in Land System IIIb2 (Table 18, Column 2).

13 SORGHUM ARUNDINACEUM GRASSLAND Physiognomy A tall floodplain grassland standing to 5 m (16 ft) high. Dominant Virtually a pure continuous stand of S. arundinaceum. floristics Environmental * The southern equivalent of Community 30. These grasslands are subject to intense relationships burning and are probably a fire-induced disclimax of Communities 10 and 17, occurring on vertic clays in the Sub-Sudan Zone. However, further study is needed and such factors as duration of flooding could also affect the distribution of this community. Species list None.

14 BOSWELLIA/ACACIA spp. SAVANNA WOODLAND/TREE SAVANNA Physiognomy Scattered trees, sometimes with more dense local groupings, standing to 7-9 m (23-30 ft) with typically a well developed ground cover of shrubs beneath. Dominant This community is characterised by the dominant presence of Boswellia, Acacia floristics dudgeonii or A. hockii and Combretum glutinosum. Environmental This community replaces Communities 2 and 9 either under more dry Sudan climatic relationships conditions or under markedly adverse edaphic conditions, steep slope, very stony shallow soils in the Sub-Sudan Zone. Elements of the leguminous woodland are typically present but these disappear under increasing Sudan conditions, and this community grades into Community 21. A. hockii tends to replace A. dudgeonii on basalt-derived soils and in the southeast of the project area. Species list Based on 0.2 ha (0.5 ac) plots in the middle Gongola Valley on Basement and Bima Sandstone-derived soils (Table 18, Column 3). Based on 0.2 ha (0.5 ac) plots on basalt soils in the Biu Hills, Land System IVcl (Table 18, Column 4). A traverse across Basement and Bima Sandstone units in the area of Song, Land Systems IIa7, Id7 and Ic3 (Table 19, Column 1).

15 HAEMATOSTAPHIS/BOMBAX WOODLAND/TREE SAVANNA Physiognomy Localised stands of tall woodland with emergents reaching as high as 30 m (100 ft). Dominant A specialised community characterised by the presence of H. barteri and B. costatum floristics associated with a group of species more typical of riparian and parkland vegetation, Diospyros mespiliformis, Ficus spp., Adansonia digitata and Vitex donniana. Pterocarpus erinaceous is common. Environmental The so-called 'Inselberg Community'. In the project area typical of deeper soils relationships and colluvial pockets associated with rock clefts on the hills of the Basement Complex but also occurring on similar sites on the Bima Sandstone. Typically found scattered among the thin-soil communities* of the Sub-Sudan and Northern Guinea Zones. A symbol is employed on Map 4 to indicate areas where it is particularly conspicuous. Species list None.

136 SPECIES LIST Table 18

Community Number 12 12 14 14 Community Number 12 12 14 14

Common trees & shrubs Comnon species on llthosols MAR>9O0nn (30 In)

Balanites aegyptiaca Acacia dudgeonl . _ Sterculla setlgera Burkea afrlcana , „ Anogelssus lelocarpus Acacia hockl! '. . Lannea schlmperl Afzella afrlcana . Bombax costatum Isoberllnla doka _ SI Prosopls afrlcana I. dalzlelll . . Pterocarpus erlnaceous Honotes kerst lngll . . Sclerocarya blrrea Haematostaphls barterl . Entada afrlcana Combretum molle c. ghasalense _ C. glutInosum _ Feretla apondanthera _ Gulera senegalensls Combretum aeuleatum . Zlzlphus maurltlana Securlnega vlrosa . Plllostlgma retlculatum— Capparls spp. . Cassia slngueana Acacia ataxacantha . _ Annona senegalensls Dlchrostachys glomerata Crewla mollis _ Grewla flavoscens . Gardenia spp. - G. laslodlscus . . ;: Xlmenla amerlcana Clssus quadrangularls _ Maytenus senegalensls Pseudocedrflla kotschyl , Commiphora afrlcana Nauclea lat 1 folia _ C. pedunculata Lannea humllis _ Zlzlphus mucronata Acacia seyal . A. pOlyacantha/campylacantha. Common trees & shrubs MAR > 750 mm (30 In) A. sleberiana - Mltragyna Inermls - Steganotaenla arallacea Stereospermum kunthlanum Trees of farmland and fallow Securldaca longepedunculata Hexalobus monopetalus Adansonla dlgltata . Termlnalla brovmll Acacia alblda _ Hannoa undulata A. arablca var. adansonll Heerla Inslgnls Tamarlndus lndlca ' . Trlchllla roka Dlospyros mesplllformls Vltex slmpllclfolla :!: Flcus spp. - Adenodollchos panlculatus Borassus aethloplcum . Swartzia madagascarlensls Butyrospermum paradoxum Hymenocardla aclda — Vltex doniana — - Pteleopsls suberosa 1 Park la clappertoniana , Grewla vlllosa — Danlellia ollveri - Pavetta sp. Khaya senegalensls — . Ochna schwelnfurthiana Cussonla barterl Riverain species Amblygonocarpus andongensls Parlnarl curatelllfolla Tetracers alnlfolia - P; polyandra Syzyglum gulneense - Combretum blnderlanum Pteleopsls habeensls . C. hypopillnuTj Termlnalla macroptera - C. nigricans var. ell lotll Alchornea cord 1 folia — - Termlnalla avlcennloldes Macaranga schweinfurthll T. laxlflora Hlmosa plgra - Plllostlgma thonnlngll — Mlllettla thonnlngll • Locally common or rare trees and shrubs Irvlngla smlthll - •Tcebergla senegalensls - HAR 500- 1 000 mm (20 - UP In) Paullinla plnnata - Malacantha alnlfolia . Dalbergla melanoxylon Mltragyna clllata — - Cassia sleberlana Klgella afrlcana - Cassia arereh Raphla sudanlca • Randla nllotlea Elaels gulneensls - Alblzla chevalleri Pandanus candelabrum - Lonchocarpus sp. Garclnla ovallfolla Haerua angolensls Boscla sallclfolla Salix ledermann 11 • Celtls lntegrlfolla • Common trees & shrubs MAR < 500 mm (20 Inj Rare species Acacia raddlana A, senega! — Croton zambeslcus — . A. nllotlca var. nllotlc Gardenia sokotensls . Cordla rothll Acacia hebecladoides . Salvadora pers lea Holarrhena florlbunda . Leptadenla pyrotechnlca— Uvarla chamae - Maerua crass 1 folia Ormocarpum sp. Bauhinla rufescens — Erythrlna senegalenls Commiphora quadrlclncta— Opllta celtldlfolla . Calotropls procera — Capparls corymbosa— Cadaba farlnosa — Carlssa edulls — - Hypheane thebalca — Fadogla spp. - Allophylus afrlcanus , Common species on llthosols Antldesma venosum . Psoro spermum febrlfu Termlnalla glaucescens Boswel Ha dalzlelll Leptadenla arborea Detarlum mlcrocarpum Afrormosla laxlflora Addendun Strychnos splnosa S. lnnocua Boscla senegalensls— Brldella ferruglnea Tetrapleura sp. — Crossopteryx febriniga Securlnega rirosa Lannea sp. —

137 16 ANOGEISSÜS/ACACIA SEYAL SAVANNA WOODLAND/TREE SAVANNA Physiognomy Typically an open conformation with scattered trees, fairly widely spaced but with local denser stands. The emergents stand to 10-13 m (30-43 ft) with an understorey of scattered shrubs.

Dominant The species composition is very variable, containing the major elements of floristics Communities 10, 17, 19 and 20. In the more northerly distribution of this community A. seyal is particularly conspicuous while to the south and the southeast A. polycantha, A. hockii and occasionally .4. hebecladoides assume more importance. In parts of the southern areas, the tall grass growth leads to fierce annual fires. Here the shrub growth is depressed and scattered trees of Anogeissus, Sterculia and Entada are a feature.

Environmental An edaphic intergrade between Communities 10, 17, 19 and 20, found either on inter relationships mediate clay/loam soils or where a rapid alternation of the two soil types occurs.

Species list Based on 0.2 ha (0.5 ac) plots in the northern part of the Wagur Plains, Land System IId4 (Table 19, Column 2). Based on 0.2 ha (0.5 ac) plots in the Deba Habe - Talasse area of the Wagur Plains, Land System IId4 (Table 19, Column 3). A traverse from Yola to Song primarily on colluvial and alluvial areas (Table 19, Column 4).

17 ACACIA SEYAL SAVANNA WOODLAND/TREE SAVANNA

Physiognomy Spreading trees, usually scattered but at full development forming a closed canopy. Typical height about 5 nu(16 ft).

Dominant On certain fully vertisolic clays this community can be found comprising a pure stand floristics of A. seyal, with virtually no shrub growth, only a broad expanse of low grass cover beneath the trees. The concept of this community has however been expanded to include the association with a group of typical species like Anogeissus, Combretwn ghasalense, C. aculeatum, Balanites, Bombax and Ziziphus.

Environmental Probably best considered as the climax community on vertic clays, primarily in the relationships Sudan Zone but also capable of occurring under Sahel conditions. In the Sub-Sudan it gives way to Community 10 and, under wetter conditions, to an association with Pseudocedreia. under hydromorphic and halomorphic soil conditions it is replaced by Communities 27 and 28. Large expanses of this community occur on the Wagur Plains, Land System IId4, but more typically it forms a mosaic with Community 16.

Species list Based on 0.2 ha (0.5 ac) plots in the Wagur Plains, Land System IId4 (Table 20, Column 1).

18 COMBRETUM spp. /ACACIA spp. SHRUB SAVANNA Physiognomy Low shrubland with emergent trees. Dominant Of similar species composition to Community 16, with greater prominence of the floristics shrubby regrowth component.

Environmental The anthropic derivative of Community 16. Fallow regrowth and regenerating relationships shrubland. Species list Traverse in the Bajiram Plain, Land System IId3 (Table 20, Column 2).

138 SPECIES LIST Table 19

Community Number 14 16 1

Conmon trees 4 shrub3 Common species on llthosols MAR>90qnn (30 In)

•1 ••

•1 II 1J •• I rt0l7K.HI Pr.orwrjr-pi«: ei-1nr»ppnii

Combretum molle — H ^^•~^B J-Û— SDecles on heavy soils C. ghasalense — — — ^L. -^Bn-^| C. glutlnosum — — ^P~^Û~^P l-Wl Feretla aDondanthera I ^ | J | M Û rmnhrof.iim amilo.nr.itm • ^H ^H ^ J

Pillostlgma retlculatum —

Annona senegalensis

Maytenus senegalensis — — Harmlpa lntlfolln III l|

Conmon trees & shrubs MAR > 7SO tun (30 in) 1, a1eh»i~i.-,nn \ • N 1 M Steganotaenla arallacea .— — ^ bJ I Stereospennum kunthlanum | ,,rt,, i B 1 Renirt'lacn long*>r nc

Vltez slmpllclfolla s:::::::^ _ _ "-"ij" * V • • Adenodollchos panlculatus — \ Swartzla madagascarlensis —_ —- r. Hymenocardla aclda — —— — t. s: Pteleopsls suberosa —- — 1T h

Amblygonocarpus andongensls —_ Riverain species Parlnarl curatelllfolla-— —- -

C. nigricans var. elllotll — — Termlnalla avlcennlofdes — -— wt K-Sc. i ::ir Plllostlgma thonnlngll i.i ILL Locally conmon or rare trees and shrubs MAR 500- l 000 mm (20 - ^0 ln£

Dalbergla melanoxylon —s s ••__•_ . —S____s .. _ Alblzla chevallerl — — • -IL-I t.*_J_ C-i-1I Ir . Common trees & shrubs MAR < SCO nv\ (20 JpJ Rare species

Acanln rarlrilnnA | 1 A. spnpgfll A. nllotlca var. ni lot lea . CnrHIa r«r.h11

Leptadenla pyrotechnlca— —- MflOT-ila rr-acfllfrtl la

Commiphora quadrlclncta — npilia ceUlrtl folia . .

Common species on llthosols

Rnmn>111a rlAl« 1*111 s •tH ^ J1t Strychnos splnosa — — — — — H B 1• Addendum ET it [J KB« Brldella ferruglnea — •LJn nC JITt Crossopteryx febriruga — •jt~jl SecurineRa »irosa

139 SPECIES LIST Table 20

Community Number 17 18 Community Number 17 18

Common trees * shrubs Connon species on llthosols MAR>9QCttn (30 In)

T, rtfll-rleHf

Srler-nrsrya MIT-OJI 1 ^ |

slur 1nn«t«n ^H PP^

innnnq ponPP«l»»n

Conmon trees & shrubs MAR > 750 mm (30 In)

Rlvsraln species

Locally common or rare trees and shrubs MAR 500- 1 000 mn (20 - iiO In)

Dfllhprgla fnplannxylnn 1 1

IN 1111 1 II I

Connon trees & shrubs MAR < 500 mi (20 lp} Rare species Ar.nr.in rnHrtlnna

Ormnrqrptim sp.

npllln rolMrllfnl !n

Par! <:«:» ortjil 1«:

Connon species on llthosols

Boswellta dalzlelll _ J,

Adderyiun

LiecunneRa virosa

140 tb..

i>v- ,' "1-- '«4. .'v7f* - 'Vi'•*&?•' *. ^ -VH V! ^•'^ .is

PLATE 1/13 acacia seyal Tree Savanna on vertic clay flat. March 1967.

IM*.

PLATE 1/14 Land System Vel, the Arege Plain. Cordia rothii/ Acacia raddiana Tree and Shrub Savanna. Thickets of Salvadora persica can be seen. March 1967.

141 19 ANOGEISSUS WOODLAND/TREE SAVANNA

Physiognomy Typically an open woodland standing to 10-15 m (33-50 ft) high with no distinct strata but with emergent trees and a diffuse layer of smaller shrubs and trees.

Dominant In its typical form this community is fairly rich in species. Trees such as the floristics dominant Anogeissus with Bombax, Sclerocarya and numerous others form the upper canopy. In the lower levels Guiera and Combretum glutinosum are the major shrubs. A more northerly drier variant can be recognised where species such as Acacia Senegal, Commiphora spp. and Dalbergia become more conspicuous.

Environmental The characteristic community of unfarmed areas in the Sudan Zone. Good examples relationships are to be seen in the forest reserves of the Damaturu Plain, Land System Vc2. On shallow soils it intergrades with Communities 9 and 14. On heavier or more silty soils tending to hydromorphism there is an increasing tendency towards thicket formation.

Species list 'Typical form'. Based on observations in forest reserves in the Damaturu Plain, Land System Vc2 (Table 21, Column 1). •Northern variant' . Based on observations in Land Systems Vc2 and 3 (Table 21, Column 2). "Moist variant'. Intergrading to Community 20. Based on observations in Land Systems Vc2 and 3 (Table 21, Column 3).

20 ANOGEISSUS/ACACIA ATAXACANTHA WOODLAND/TREE SAVANNA* Physiognomy Similar to Community 19 but with a regular interspersed pattern of dense thickets. Dominant Similar to Community 19 but tending towards Community 16 in character. The major floristics thicket species are Acacia ataxacantha, Capparis tomentosa, Cissus quadrangular is, Combretum aculeatum, Grewia flavescens, G. lasciodiscus, Securinega, Ziziphus mauritiana, Z. mucronata, Dichrostachys and Feretia. Environmental Occurs in the same climatic range as Community 19 on heavier soils tending to relationships hydromorphism. As a mapping unit, it is shown as occurring in Land System Vc2 where it occupies extensive tracts of land. Localised pockets do however occur throughout the Anogeissus Woodlands. Species list Traverse in Land System Vc2 (Table 21, Column 4).

21 BOSWELLIA WOODLAND/TREE SAVANNA Physiognomy Occasionally an open woodland but more typically a tree savanna of scattered trees standing to about 10 m (30 ft) with limited shrub growth beneath.

Dominant The floristics of this unit are not fully known for the project area although floristics similar communities are described for Cameroon (Letouzey, 1968). It would appear to differ from Community 14 primarily in the greater predominance of Boswellia, which can sometimes occur in nearly pure stands, sterculia setigera is a common accompanying species, and accompanying shrubs are usually limited in number.

Environmental Best considered as the typical community of lithosolic sites in the drier sector relationships of the Sudan Zone, perhaps extending into the Sahel. It probably also occurs on extremely rocky sites under wetter climatic conditions. It is for example very common on volcanic plugs and has been mapped as occurring in the northern part of the Mandara Mountains, Land System Ic2-

Species list None.

* Tangled thickets of similar species composition also occur in Communities 10, 16, 17, 27 and 28.

142 SPECIES LIST Table 21

Community Number 19 19 1 9 20 Community Number 19 19 19 20

Common trees & shrubs Common species on llthosols MAR>900mn (30 InJ^

A re gels sus lelocarous ^^P^P'~fl Lannea schlmperl -— — — ^ 1

• T, rtat7l\t>yi1

1 BH Haematostaphls bartert

H-^H-4-l Species on heavy soils

H-^^H- npnnrtanfh«™ H^ • •• ^M

Plllostlgna retlculatum —- — ^B~~^U~~W

Common trees 4 shrubs MAR > 750 mm (30 In)

--- •'•'•'

An'blyeflnn''^rTl,is andonpensls Riverain species —i i •

Locally common or rare trees and shrubs MAR 500- 1 COO mm (20 - ^0 lrj2

Dalbergla melanoxylon 11 JB l_l Cassia sleherlana 111 Cassia arprPh U . Rnndla nllntir» H Q Alhlr.tn rhpvallppi T/inrhnrarpns RJ^ | |

Comon trees & shrubs MAR < 500 mm (20 JpJ Rare species Acacia raddlana A. senepal 1 II 1

Salvadora pers|r>a

nrmnrprr^im Sp,

npllla rPlMrtlfnllA

Common species on llthosols

Boswellla dalzlftlll V

I • aaaenaun • M~ • •

SecurineRa »Irosa l.ann»a sp.

143 22 ACACIA SENEGAL/COMBRETUM GLUTINOSUM TREE AND SHRUB SAVANNA Physiognomy A low open shrubland with emergent trees. When protected, as in some of the forest reserves, a dense tall shrubland/woodland up to 5 m (16 ft) in height can develop.

Dominant The shrub component of this community is virtually identical with that of the floristics shrub savannas described under Communities 23 and 24. It differs in possessing a high proportion of low tree growth, the characteristic species being A. Senegal, Commiphora pedunculate and usually Dalbergia.

Environmental Considered to be an anthropic derivative of the more northerly Anogeissus Wood relationships lands of the Sudan Zone. It is thought to be an intermediate impact level community, reverting to Anogeissus Woodland if protected and giving rise to Communities 23 and 24 under more intense utilisation. The available records in the project area come from the central sector of the Lantewa Dunefield but the known distribution of the gum-arabic producing areas indicates that this community occupies a considerable area of the sand plains and dunefields, as shown in Map 4.

Species list Based on 0.04 ha (0.1 ac) plots south of Lantewa in Land System Vcl (Table 22, Column 1).

23 GUIERA /COMBRETUM GLUTINOSUM SHRUB SAVANNA Physiognomy Variable, ranging from an open to dense cover and from low fallow regrowth to a near tree and shrub savanna up to 3 m (10 ft) in height. Occasional residual trees may occur.

Dominant The species composition of this community remains remarkably homogeneous despite floristics wide variation in site history. C. glutinoaum and Guiera as the co-dominants occupy by far the greater part of the arboreal cover. The remnant trees are usually Anogeissus, Sterculia or one of the other common Sudan Zone woodland species. In young fallows Ziziphus mauritiana and Cassia singueana are usually more conspicuous while, with increasing age, elements typical of the Anogeissus Woodlands increase in importance. Environmental The typical regrowth community of the central belt of the Sudan Zone. It is relationships associated with a fairly high level of anthropic impact (see also comments under Community 29), distributed about the 750 mm (30 in) isohyet, and occurs as a climatic intergrade community between Communities 24 and 12.

Species list Based on 0. 04 ha (0.1 ac) plots and traverses in the Damaturu/Goniri area, Land System Vc2 (Table 22, Column 2).

24 GUIERA SHRUB SAVANNA Physiognomy An open shrub savanna with few emergent trees. Occasional more dense cover can be found where there is some degree of protection.

Dominant Dominated by Guiera, not uncommonly found in near-pure stands. Associated species floristics are variable but commonly include Ziziphus mauritiana, Comb re tum glutinosum, Piliostigma reticulatum, Boscia senegalensis and Calotropis procera. Environmental The typical regrowth community on free-draining soils in the northern Sudan Zone, relationships impinging slightly into the Sahel Zone (see comments under Community 29). Species list Traverses in the Gulumba area. Land Systems Vil, ViS, and Vh2 (Table 22, Column 3). Traverses in the Gashua - Geidam area, Land Systems Vcl and Vfl (Table 22, Column 4).

144 SPECIES LIST Table 22

Community Number 2 2 23 24 24 Community Number 22 23 24 24.

Common trees & shrubs Common species on llthosols MAR>900mn (30 In] • 1 ACAMA riiiri mnn 1 niiHrpa afrfrana

Af7.pl In afrtcana

s 1, dalzlelll 1 1

Feretla apondanthera 1 •• HI Hnrnhrptim amilpnT.irm 1 1 1 • 1 Zlzlphus maurltlana — — y- Securlnega vlrosa 1 I • Plllostlgma retlculatum 1- Capparls spp- 1 3—0—0.1.- Cassla slngueana H- Lt 1pÉÉrp__ 1 Dlchrostachys glome rata 1 L l_ s W Crewla flnvrsnpns ,. 1 r• Sil " . 1. \ Clssiis miadranpiilarls Pseudocedrela kotsehyl Hauelea lat1 folia • - - -. n• Acacia spyal 'II JÊ II A. pOlyacantha/campylacantha Comnon trees & shrubs MAR > 750 mm (30 In) A. slPhprj.nna ::ff: :":: it __LL : :___ ir__::~ _jr _jr

A. arablca var. adansonll III TamarlnriiK 1 nH 1 r A -T Iff-^ff Dlospyros mesplllformls "Ilit- _!it-its - Plcus spp. - :JT Borassus aethloplcum Butyrospermum paradoxum . Vltex doniana — - Park la clappertonlana Danlellla Oliver* -

Riverain species

, Tetracers alnlfolia

Syzyglum gulneense

C. nigricans var. elliotll -. Termlnalla macroptera Termlnalla avlcennloldes ff rnr • \ Macaranga schwelnfurthll —

Mllletm thonnlngll Locally common or rare trees and shrubs MAR 500- 1 000 mm (20 - W> In) Dalbergla melanoxylon — — — II PU- _JL " :: A::: ::i: s Raphla sudanlca — Pandanus candelabrum Care In la oval 1 folia "":: _s:__ Common trees & shrubs MAR < 500 mm (20 Inj Rare species" AcaMn mrifllftna win .ZLT '~]*~ '- k HnrrtPnta snVnr.on«!ts in i Ar.-iMa hPh*»M.iHn1rlP* Hnlarrhena flnr-lhunrtn Uvarla chamae — 1 " --] •1 Erythrlna senegalenls — HplHfl pplMrtlfnlla " Jl Capparls corymbosa— "•• 1 lir' "ITT -\H Fadogla spp. Allnphylii«! afrlrnnii« AnMr1f>

Tetrapleura sp. -*_ •-I--II Securlneea vlrosa T lannpa «tp t±

145 25 ADANSONIA PARKLAND Physiognomy Farmland and farm fallow with widely spaced individual tree standing to as much as 20-30 m (66-100 ft) at full maturity. Some low shrub regrowth. Dominant The herbaceous cover is described in part in Volume 4. The regrowth shrubs are floristics those typical of Communities 23, 24 and 29. Adansonia digitate is the most common parkland tree with other economic and shade trees such as several Ficus spp. Remnant species from the original Anogeissus Woodlands do however occur. Environmental Typical of long-standing intensive cultivation in the Sudan Zone on free-draining relationships soils. Species list None.

26 ACACIA ALBIDA PARKLAND Physiognomy Farmland and farm fallow with widely spaced individual trees standing to 15 m (50 ft) in height. Restricted low shrub regrowth. Dominant The herbaceous cover is described in part in Volume 4. The regrowth shrubs are floristics those typical of Communities 24, 29 and occasionally 33. The trees are almost entirely Acacia albida. Environmental Typical of long-standing cultivation in the northern Sudan Zone but extending both relationships into the Sahel Zone and drier areas of the more southerly Sudan Zone. Species list None.

27 ACACIA spp./BALANITES TREE AND SHRUB SAVANNA* Physiognomy Typically tree and shrub savanna sometimes developing into a savanna woodland. Dominant This unit is best considered as an ill defined grouping of communities. It is floristics nevertheless a convenient mapping unit for an interrelated complex of plant associations characterised by the dominant presence of Balanites aegyptiaca and Acacia seyal. it differs from Community 17, which is essentially a tree savanna composed of either a pure stand of A. seyal or A. seyal with a limited proportion of accompanying species, in exhibiting a more heterogeneous species composition associated with a number of other Acacia spp. It includes for example the A. seyal and A. Senegal thicket in the interdune depressions of Land System Vh2 (Pullan, 1969), the A. seyal and A. nilotica var.nilotica tree savanna of the cracking clay plains of the northeast (Higgins et al. i960) and the 'Acacia bushland and wooded grassland' described by Clayton (1957) in the Hadejia floodplain (see comments under Community 28). Environmental Found on heavy soils throughout the project area. In the Sub-Sudan Zone it tends to relationships be replaced by Communities 17 and 10 on the vertic clays, but elsewhere it is distributed over the hydromorpnic, halomorphic and vertic soils. As halomorphism becomes pronounced it tends to give way to Community 28. Species list Traverse from Gashua to Geidam, Land Systems Vfl and Vg2 (Table 23, Column 2). Traverse near Gulumba, Land Systems Vil, Vi3 and Vh (Table 23, Column 3). Observations near Yobe river. Land System Vf3 (Table 23, Column 4).

28 ACACIA spp./BALANITES/LANNEA HUMILIS TREE AND SHRUB SAVANNA* Physiognomy Typically tree and shrub savanna sometimes developing into savanna woodland. Dominant This unit is best considered as a variant of Community 27, characterised by the floristics additional presence of conspicuous gregarious clumps of Lannea humilis. There is no clear division between the two communities but if L. humilis is present in significant proportion, then the vegetation should be classified under this heading. Environmental Found on heavy soils with a marked tendency to halomorphism throughout the Sudan relationships and Sub-Sudan Zones in the project area. Species list Traverse near Gulumba, Land Systems Vil, Vi3 and Vh2 (Table 23, Column 1).

* Thickets of Acacia ataxacantha and associated species are common in these units, often associated with termitaria.

146 SPECIES LIST Table 23

Community Number 28 27 27 27 Community Number 28 27 17 27

Common trees & shrubs Common species on llthosols MAR>900mn (30 In)

ll_Hfl_ ACACIA dudReoni

T, rtn1«t»11f

_ - - - rnmhi-ofjim flMilnflT.llm H H HQ Zlzlphus raauritlana — — — ^P ~ff^ ~l ll_ll SpeurlnftRA vlrosa II M ^M

Common trees & shrubs MAR > 750 pm (30 In) A, sUhPrmnn Ml IM •! •

Riverain species

Locally common or rare trees and shrubs MAR 500- 1 000 mm (20 - ifO in)

Dalbergla melanoxylon CassiA sipfr»r1arvi

Ranrlln nllotlcA

Common trees & shrubs MAR < 500 mm (20 \f\) Rare species Acacia rarirttnna ^L | J |

Sfllvarlnra ppr«ijf*fl

• .Ormocarpum sp.

[I Opilla ceir-frtimiffl

Common species on llthosols

Addendum

securineea Tirosa

147 29 ZIZIPHÜS/ACACIA spp. TREE AND SHRUB SAVANNA Physiogonomy Scattered shrubs and regenerating trees with occasional emergent residual trees. Dominant Essentially the same species composition as Communities 27 and 28 but with a far floristics higher proportion Of Z- mauritiana. Environmental Degraded shrub community resulting from anthropic impact on Communities 27 and 28. relationships However, it would appear that under particularly severe impact, this community can replace Communities 24 and even 23 on free-draining soils although it is normally considered a heavy-soil type. This feature is particularly conspicuous in the heavily populated, intensively farmed sand plain and dune areas in the alluvial complexes in the northwest of the project area, where the proximity to the hydromorphic regime may have some influence on the vegetation. In other areas this community is found on light soils overlying heavy soils.

Species list Traverse near Gulumba, Land Systems Vil, Vi3, Vh2 (Table 24, Column 1). Derived from Clayton (1957) (Table 24, Column 2).

30 SORGHUM AETHIOPICUM GRASSLAND Physiognomy Tall floodplain grassland standing to 5 m (16 ft) high.

Dominant Virtually a pure stand of S. aethiopicum above a low ground cover of hydromorphic floristics herbs and grasses. Environmental The northern equivalent of Community 13, occurring under similar conditions on the relationships cracking clay plains about Lake Chad.

Species list None.

31 ACACIA RADDIANA TREE AND SHRUB SAVANNA Physiognomy An open tree savanna with scattered trees standing to 12 m (40 ft) and with scattered shrubs.

Dominant Dominated by A. raddiana associated with A. Senegal and Balanites. of the shrub floristics cover, Leptadenia pyroiechnica, Calotropis procera and Boscia senegalensis are common species.

Environmental The typical community of free-draining soils in the Sahel Zone. Along the line of relationships the 500 mm (20 in) isohyet it grades into the Xnogeissus-dominated communities of the Sudan Zone.

Species list Traverse in the Banawa Dunefield, Land System Vd2 (Table 24, Column 4).

32 CORDIA ROTHII/ACACIA RADDIANA TREE AND SHRUB SAVANNA (WITH THICKETS)

Physiognomy A mosaic of open tree savanna interspersed with areas of aggregated small trees and shrubs which can develop into tangled thickets with a dense growth of climbers supported by the erect growth.

Dominant Can be considered as a variant of Community 31, with the A, raddiana Tree and Shrub floristics Savanna forming a matrix in which are dispersed the thickets of Cordia rothii, Commiphora africana, C. quadricincta with the climbing Salvadora persica and Leptadenia arborea.

Environmental In the project area this community occurs only in the extreme northeast, where the relationships mean annual rainfall falls below 380 mm (15 in). It is common on the sands of the Arege Plain, Land System Vel and on the sand islands of the Yo Alluvial Plain, Land System Vf3.

Species list Traverse in the Arege Plain, Land System Vel, (Table 24, Column 3).

148 SPECIES LIST Table 24

Community Number 29 29 32 31 Community Number 29 29 32 31

Common trees & shrubs Cotranon SDecies on llthosols MAR>30Qm £J0 lnj_ / firaria rtifrifpnnl •• • RurkM afrtcnn» Arafin hnrfclt AfzflUa afriranA

S T rtfli7.uill

t C. glutlnosura — l~~ \ \ RpfflirlnARa vtmsft ^1 M Plllostlgna retlculatum — Ml. -Jpi- __1 .

s Pseudocedrfila kntsrhyl Hauelea lat I folia . --T--4 -TTT t__i u \ A, prtlyarnnr.hn/rampylfl^anr.ho ^H | Common trees A shrubs MAR > 750 mm (30 (n)

Trees of farmland and fallow

wansnnlfl dlfjltnta II •! H • Ar.nr.in alhida W PW • P

VIT.*»» «ImpllrtfnllA

Riverain species ,

Locally common or rare trees and shrubs MAR 500. l COO mm (20 - ^0 In)

Dalberg!» mPlannrylnn S

Common trees & shrubs MAR < 500 mm (20 jnj Rare species Acacia raddlana M — • A. spnpgal 1 - -W • i - --U. - -JÉ —• l IIvartA rhAmap i :•• ~l*~Jr --]-T npllln nPltlrtlfnl \n t"' ~mI M V' ' 'JLH ' ~TT H

Rnmmllln rinlKlulM

Addendum

Securlneea »Irosa linnen sp. _I_

149 33 LEPTADENIA SHRUB SAVANNA Physiognomy An open shrub savanna with few emergent trees.

Dominant A species composition similar to Community 31 but with the tree cover destroyed, floristics

Environmental An anthropic derivative of Community 31. relationships Species list None.

34 ARISTIDA/ANDROPOGON GRASSLAND Physiognomy A well developed grassland standing 1-2 m (3-6 ft) high. Shrub growth is rare but occasional tall emergent trees occur, standing to 10-13 m (33-43 ft).

Dominant The sward dominated by Ariatida spp. and Andropogon gayanua. This has been floristics described as var. bisquamulatus but is more probably the sub-Saharan var. tridentatua. The emergent trees are almost entirely Acacia albida and Sclerocarya birrea. Environmental This community, the so-called 'Manga Grasslands', occurs only in the far north of relationships the project area on the extremely free-draining dune of the Zigindi Plain, Land System Vbl. It forms a break in the otherwise continuous belt of Acacia raddiana Tree Savanna (Community 31). It has been suggested that resorting of soil particles resulting in a change of mechanical composition, in particular the fine sand/coarse sand ratio, can effect a swing from annual to perennial grassland. Further studies are required to elucidate fully the relationships of this interesting community.

Species list None.

35 CHAD FRINGE COMPLEX Apart from Mimosa pigra and occasionally elements of Community 36 on island sites, there are no woody communities of significance in this complex. It is dealt with under 'Grassland' in Volume 4.

150 36 NORTHERN ALLUVIAL COMPLEX The spatial relationship of the major plant communities in this complex are shown in Figure 15. In addition to elements of Communities 27, 28, 29, 31, 32 and 33, the balance of the woody vegetation can be considered as comprising two plant communities, listed below as 36a and 36b, distributed along rivers and streams and alluvial plains in the northern Sudan and the Sahel Zones.

36a HYPHAENE PALM SAVANNA AND PALM BUSH

Physiognomy At full development, tall dense stands of the palm attain heights of the order of 10 m (33 ft). Where heavily utilised, thickets of palm regrowth develop.

Dominant Near-pure stands of H. thebaica with occasional shrubs of Ziziphus spp. and floristics Acacia spp. Environmental Favoured sites are sand islands and sand drift either over, or influenced by, relationships halomorphic clays.

Species list None.

36b MITRAGYNA/ACACIA NILOTICA RIPARIAN WOODLAND Physiognomy Tall fringing woodland standing to as much as 13 m (43 ft) high. Dominant Dominated by M. inermis and the varieties of A. nilotica and other Acacia spp. floristics Kigelia africana is not uncommonly found in this community.

Environmental River and stream banks. Wet islands in floodplains. relationships

Species list None.

151 37 SOUTHERN ALLUVIAL COMPLEX

The spatial relationship of the major plant communities in this complex are shown in Figure 15. In addition to elements of Communities 10, 16, 17, 18, 27, and 28, the balance of the woody vegetation can be conveniently classified as four plant communities, listed below as Communities 37a to 37d. This complex occurs in the major part of the Sudan Zone, the Sub-Sudan Zone and, excepting the Deji/Gaji river system on the Kerri Kerri Plateau (Land Systems Illbl and IIIb2), the Northern Guinea Zone within the project area.

37a BORASSUS PALM SAVANNA Physiognomy Tall, often regularly spaced stands of the palm attaining as much as 25 m (80 ft) in height. Usually in floodplain grassland with limited low shrub growth beneath.

Dominant Near-pure stands of B. aethiopicum. Shrub growth is typical of Community 12. floristics

Environmental In the project area confined to floodplains or sometimes river terraces with high relationships watertables. Species list None.

37b MITRAGYNA/CELTIS RIPARIAN WOODLAND Physiognomy Typically closed woodland at full maturity with tall trees rising to as much as 25-30 m (80-100 ft) in height. A dense understorey of low trees, shrubs, climbers and thicket species.

Dominant A variable community, M. inermis and C. integrifolia are highly typical species floristics together with Acacia spp. and several species like Khaya and Vitex also common in farm parklands.

Environmental Streamsides and water edges. relationships

Species list Based on observations on the Gongola and Kilunga rivers (Table 25, Column 1).

37c KHAYA/DANIELLIA WOODLAND Physiognomy Tall woodland, with widely spaced emergents rising to heights of the order of 30 m (100 ft). Often with a closed canopy at full development and restricted shrub growth below.

Dominant Characterised by the conspicuous presence of K. senegalensis. D. oliverii is floristics commonly also present. These are interspersed with elements of Community 19 and occasional riparian trees.

Environmental Typically forming a fringing woodland to the main riparian or swampside growth. relationships

Species list Based on observations on the Kilunga and Loko rivers (Table 25, Column 2).

37d SALIX/MIMOSA SHRUB SAVANNA Physiognomy Thick shrubland rising to 3-5 m (10-16 ft). Dominant The woody component of this community is composed almost entirely of w. pigra and floristics S. 1edermannii. Environmental Occurs on rock areas in stream beds where the Salix is particularly conspicuous relationships . and also on denuded stream banks where the Mimosa predominates.

Species list None.

152 SPECIES LIST Table 25

Community Number 37b 37c 38o 38b Community Number 37b 37c 38a 38b

Common trees A shrubs Common species on Uthosols MAR>900mm (30 In)

::ic:::::::::_ UM / T, ri»1*1pl1l

c, glirtlnnmm '

Plltostl0na ret leu la tum. /

Annona HPn^Efllpnfll'fi ' _•___

. .. j .

Common trees & shrubs MAR > 750jp £3,0 ln^ V-XX-I::II :i::::::M- : 1 1! •

L" 1 n • I Arnica fllhlrtn

. ,/ .. VU.PT fllmp-MMtolla ::::::::::JLI: . i1t mfl:._ W . .1/ fi._m m. nanlellla nl Jv0.-I 1 i a•_i MMK Riverain species -- i' ZZJK:::::: .__JL..._- it._ " "::::•::::::: __JtfL l

Locally common or rare trees and shrubs MAR 500- 1 000 mm (20 - /fO In) — ?i Dft1N>rß!a nwlanmylnn 1 :::i::::::1 : •—::ft:::::. JÉL, __: .__I--Z_._ — J•f

Common trees & shrubs MAR < 500 mm (20 Inj Rare species Acacia mddlnna

Hnl nf*rti»na Mnrlhnnrin

nrmnrai-jTÉtm pp. Frythrtna ffÄnfrealfn!« npMIn rPir.lrlffnllA _ . - _._l . <~app.ir1«t rorymhnia r^rl"^ «"^»1 '^ .7 .. Common species on Uthosols it

:: i :

153 38 DEJI VALLEYS COMPLEX The plant communities associated with the incised valleys in the Kerri Kerri Plateau, Land System Illdl, are unique in the project area and carry a vegetation typical of more southerly wetter areas of Nigeria. In the light of our present knowledge the woody communities can be conveniently classified under four main headings, 38a to 38d below. Further investigation could well justify further subdivision of this classification. The vegetation is probably a reflection of near Northern Guinea climatic conditions, the persistence of flow in the rivers themselves and the low anthropic impact in this area.

38a RAPHIA/MACARANGA RIPARIAN FOREST Physiognomy Dense forest with emergents rising to over 30 m (100 ft) with a confused well developed series of sub-storeys. There is a rich shrub layer and ground flora. Dominant Dominated by palm species, particularly R. sudanica. There is a high proportion of floristics broad-leaved trees. High stands of Pandanus candelabrum are a feature. Environmental Occupying the banks of the rivers and swamps of the complex. relationships Species list A partial list based on Keay (1962) and Tuley (1970) (Table 25, Column 3).

38b FICUS CONGENSIS WOODLAND THICKET Physiognomy Dense close stands of colonial fig with numerous stilt roots, standing to as much as 12-15 m (40-50 ft) high. On some islands it occurs as an outer waterside zone with an inner core of slightly higher broad-leaved trees. Dominant Pure stands of F. congensis. The associated species in the zonal areas appears at a floristics distance to be a Syzygium sp. but could be one of the similar broad-leaved trees like Garcinia ovalifolia. Species 1 ist None. -

38c KHAYA/DANIELLIA/PTELIOPSIS WOODLAND Physiognomy Tall woodland standing to about 15 m (50 ft) with typically a closed canopy and restricted shrub growth beneath. Dominant Very similar to Community 37c but differing primarily in the more conspicuous floristics presence Of D. Oliverii and Pteliopsia spp. Environmental Occurs as a belt of fringing woodland between Community 38a and the interfluve relationships vegetation. Species list Based on Keay (1962) and Tuley (1970) (Table 25, Column 4).

38d PTELIOPSIS HABEENSIS WOODLAND THICKET Physiognomy Physiognomically unique in the project area. The trees comprise numerous thin trunks, coppice-like and uniform in thickness. A woodland thicket is formed rising to 10-13 m (33-43 ft) in height. Little light is admitted and the ground cover is sparse.

Dominant Pure stands Of P- habeenais. floristics Environmental Occurs along the smaller streams running into the main rivers. The reason for its relationships occurrence is by no means clear but it appears to be associated with a combination of a riparian habitat with exposed or near-exposed rock in the valley bottoms. Sandstone rock is invariably exposed in the stream bed where this community occurs, sometimes carrying 'rock species' like Croton zambesicua. The woodland thicket commences a few yards back from the stream bank and occupies a belt some 20-45 m (70-150 ft) wide. Species list None.

154 1^f^'^" ^^5|$ÉÊ&&

>•&*&

PLATE 1/15 Hyphaene Palm Bush on the Yobe Ploodplain.

PLATE 1/16 Riparian Woodland on the course of the River Yedseram. north of the Bama Ridge. March 1967.

155 FAUNA by P J Aitchison and P E Glover

Wild animals, apart from small mammals, birds, lizards and monkeys are not common in the North East project area except in a few remote tsetse-infested areas like the Yankari Game Reserve and the reed and papyrus swamps around Lake Chad. This paucity in the fauna is in sharp contrast to East and Central Africa. Nevertheless a large variety of species have been recorded from the area (Rosevear, 1953).

MAMMALS

Of the more spectacular game animals, herds of elephant, Loxodonta africana, have been seen in the Gongola Valley and in the swamps near Pika. Bushcow or buffalo, Syncems nanus, are widespread but shy and seldom seen, occurring in the Guinea and Sudan zones but not in the Sahel zone. Giraffe, Giraffa camelopardalis peralta, is reputed to occur in the Yankari Game Reserve. In the past, they have been recorded near Azare and near Biu, but they are now either extinct or exceedingly rare. The black rhinoceros, Diceros bicomis, has been recorded in the North East but it has not been seen for many years. Hippopotamus, H. amphibuus, is found in the Benue river, the Gongola and its tributaries, and in the swamps of Lake Chad.

Lists of the more common mammals found in the project area are shown in Tables 26-31, at the end of this section.

REPTILES Among the larger reptiles, three species of crocodile occur in northern Nigeria: the Nile crocodile Crocodylus niloticus; the long-snouted crocodile C. calaphactus; and the broad- fronted crocodile Osteoloemus tetraspis. The sacred crocodiles in Lake Tilla near Biu are well known. Two species of monitor lizard are common, the aquatic Varanus niloticus and the land lizard V. exanthematicus. Large yellow, red and blue Agama lizards are abundant everywhere and chameleons are regularly seen. Snakes are numerous, although not often seen, three of the more common ones being puff adders, cobras and pythons.

BIRDS In contrast to the scarcity of large mammals, birds are numerous in the North East. Vultures and crows are common around most of the towns and villages. Magpies are said to be associated with the presence of Borassus palms (Elgood, 1960). Storks, pelicans, crested cranes, egrets, ducks and a number of other birds can be seen wherever there is water, especially on the shores of Lake Chad and along the rivers running into it (Buxton, 1935). The ostrich occurs, but is now very rare indeed. Bush fowl, Francolinus, are ubiquitous, particularly one species which lives in the gardens around the towns and villages; guinea fowl, both wild and domesticated, are common everywhere. Smaller birds such as pigeons, waxbills, sparrows, weavers, sunbirds, thrushes, cuckoos, shrikes, orioles and starlings are abundant. Weavers often assume the proportions of a major agricultural pest (Crook and Ward, 1968; PAO, 1965).

INSECTS Pull treatment of this topic is clearly beyond the scope of this study. Bibliographic data are however widely available and Posnett et al. (1971) is of specific application to Nigeria. Tsetse and related biting flies are the subject of Volume 2. Due to their impact on land resources the following merit special, if brief, mention.

156 Locusts The North East is particularly sensitive to attack by both the Desert and Migratory Locust. Although free of major attack for some years, there have been recent up surges and there is no justification for relaxing vigilance. Apart from spectacular attacks, considerable routine damage is done by non-gregarious forms (Betts, 1961; Bullen, 1969; Popov and Ratcliffe, 1968; Waloff, 1966).

Simulium This fly and the dreaded disease of river blindness that it carries are prevalent in the Hawal and Kilunga/Loko river systems. It is often the limiting factor in the develop ment of fertile alluvial areas (Hunter, 1966; Ovazza et al. 1965).

Termites These insects play a significant role in the ecosystem, particularly in the tropical environment obtaining in the project area. They can be pests of crops, destructive to wooden structures and active in pedogenetic processes. The distribution of species and the characteristics of their nests and mounds can be employed as useful indicators of such environmental parameters as soil type, water regime and fire regime (Bouillon, 1964).

EXTERMINATION OF GAME

Apart from Rosevear (1953), there is very little information about present-day wildlife in the North East. On a tour covering more than 6 500 km (4 000 mi) between October and November 1965, and taking 6 weeks, the writers saw 2 red-fronted gazelle in a field near Song, a couple of warthog, several troops of baboons and some monkeys. Hyaenas were heard in a few places at night. At Potiskum hyaenas are sacred and a number of them live in caves in the ironstone. Two baby hyaenas were seen on a lead in the town.

Davies (1956) gives a list of animals found in the Biu area during his time there. He mentions lion, leopard, cheetah, wild dog, hyaena, jackal, bushcow, roan antelope, waterbuck, kob, gazelle, reedbuck, duiker, two species of hartebeest. and even giraffe and aardvark. During our stay of a week at Biu we saw not even one of these animals. Davies also mentions that there has been a great reduction of game in the area in the past 50 years and says that a missionary wrote of a hunt in 1931-32 in the Garkida district reporting that he saw 15 roan antelope, a drove of 30 pigs, numerous small antelope, a big warthog, reedbuck, waterbuck, bushbuck, buffalo, lion, a herd of 16 giraffe, a drove of 50 baboons and some hyaenas. He seems to think it unlikely that all these animals could have been seen on one hunt, but in parts of East Africa even today it would be possible to see that number of animals in the course of an hour or so. In the 15 months that Davies spent at Biu, which included about 100 days on tour, he saw only baboons, monkeys, duiker, gazelle, leopard and hyaena and also a variety of small mammals, snakes and insects. However, the true situation regarding the abundance of game in this area in the past is confusing because Davies quotes the following passage written in 1907 in the Biu District Commissioner's journal: 'I am much disappointed to find how completely the game is disappearing. Some two years ago there was a fair amount of game around Wuyo'. Game drives in the Biu District which used to be arranged in the rains were rather a thing of the past by 1954, when an organised baboon hunt was not a great success.

There is no doubt that wildlife has become dangerously depleted.

In most modern societies regulated hunting is not generally a serious factor in reducing the incidence of wildlife. In fact, it has been demonstrated (Glover, 1964) that in other parts of Africa it is virtually impossible to exterminate some of the smaller species of ungulates such as bushbuck, duiker and warthog by organised hunting. In many other territories of Africa it is not overhunting that has depleted the wildlife hut the destruction of its habitat by intensive land use and mounting human population pressure. In Nigeria however hunting would indeed appear to be largely responsible for so sadly reducing the number of game animals in most parts of the country. Petrides (1965) considers that 4 000 000 muzzle loaders or "Dane guns' is a conservative estimate for Nigeria, many of them illegally made by local 'gunsmiths'.

Where there is protein-deficiency in the diet, the economic value of "bush meat' could be, and probably is, very great. Petrides (1965) quotes March as estimating that 50 per cent of all meat eaten in Northern Nigeria comes from wild animals, but the Game Warden at Bauchi puts the figure at 25 per cent. Accepting the lower figure of 25 per cent to be more realistic, the economic value of game meat eaten in Northern Nigeria annually must be in the neighbourhood of at least £2 500 000 and this sum would increase if more animals were

157 available. Cattle, sheep and goats are incomparably more destructive to the natural habitat than a varied natural fauna. In addition the food requirements of the natural fauna are complementary and in balance with the resources of the area. Further, unlike most breeds of domestic stock, the indigenous ungulates are tolerant of trypanosomiasis.

In addition to the black rhinoceros, now extinct in Northern Nigeria, it is generally accepted that the following animals are also facing extermination: ostrich, hunting dog, cheetah, lion, leopard, giraffe, hippopotamus and klipspringer. Eventually however all the animals will go, except perhaps a few small mammals such as rodents and bats, unless a concentrated and determined effort is made now by Government to preserve more extensively this most valuable economic asset. That it can be done has been proved by the outstanding success achieved so far in the Yankari Game Reserve. It is therefore essential that as many areas of this kind should be set aside as possible. It is even suggested that if approaches were made to institutions such as the World Wild Life Fund, the International Union for the Conservation of Nature, and the East African Wild Life Society, it might be possible to hasten the process of rehabilitation by restocking with animals from the teeming game parks of eastern Africa.

158 TABLE 26 Mammals common throughout the North East

West African bushbuck Tragelaphus script us

Western defassa waterbuck Kobus defassa unctuosus

Buffon's kob Adenota kob

Aardvark/ant bear Orycteropus a fer

African wild cat Felis lybica

Egyptian mongoose Herpestes ichneumon

Marsh mongoose Atilax paludinosus

Senegal genet Genetta genetta senegalensis

Speckle-throated otter Lutra maculicollis

Cape clawless otter Aonyx capensis capensis

Ratel/honeybadger Mellivora capensis

Hunting dog Lycaon pictus

Pale fox Vulpes pallida

West Coast mammilate rat Rattus coucha erythroleucus

Giant rat Cricetomys gambianus

Nile harsh-furred rat Arvicanthis niloticus

Patas monkey Erythrocebus patas patas

Tantalus guenon Cercopithecus aethiops tantalus

Angola free-tailed bat Tadarida angolensis

Common African leaf-nosed bat Hipposideros caffer

Yellow-winged bat Lavia frons

Tomb bat Taphozous mauritianus

Pallid fruit bat Epomophorus anurus

Straw-coloured fruit bat Eidolon helvum

Nigerian hedgehog Atelerix spiculus

159 TABLE 27 Mammals recorded in the Sahel Zone

Dorcas gazelle Gaze 11a dorcas dorcas

Dama gazelle Gazel la dama dama

Situtunga Limnotragus spekii**

Scimitar oryx Oryx algazel algazel

Striped hyaena Hyaena•hyaena

Common jackal Canis aureus

Small crested porcupine Hystrix cristata aerula'

Jerboa Jaculus jaculus

Chad ground squirrel Xerus erythropus chadensis

Lake Chad hare Lepus chadensis

Diana musk shrew Crocidura hindei diana***

TABLE 28 Mammals recorded in the Sudan and Sahel Zones

Hasler's red-fronted gazelle Gaze 11a rufifrons hasleri

Senegal hartebeest Damaliscus korrigum

Soemering's cheetah Acinonyx jubatus soemeringii

Caracal/desert lynx Felis caracal

Nigerian striped weasel Poecilictis libyca rothschildi*

Senegal striped polecat Ictonyx striates senegalens is*

Mrs Buchanan' s dormouse Graphiurus olga*

Dainty fat mouse Steatomys cuppedius

Hausa pygmy mouse Mus haus sa

Kabwir spiny mouse Acomis johannis

Schlieffen's bat Nycticeius schlieffeni

* Largely confined to the north of the project area. ** Confined to the swamps round Lake Chad. *** Confined to the extreme northeast corner of the project area.

160 TABLE 29 Mammals recorded in the Sudan Zone

Side-striped jackal Canis adust us

Angelus gerbil Taterillus gracilis angelus

Nigerian hairy-soled gerbil Gerbillus gerbillus nigeriae

Buchanan' s dwarf gerbil Desmodilliscus braueri buchanani

Northern Nigerian hare Lepus ganopus

Midas bat Tadarida ruppellii

Bauchi musk shrew Crocidura arethusa

TABLE 30 Mammals recorded in the Guinea Zone

Western hartebeest Alcelaphus buselaphus maj or

Red-flanked duiker Cephalophus rufilatus

Ruddy mongoose Herpestes sanguineus

Pox's dormouse Graphiurus toxi

Fox's brush-furred rat Uranomys foxi

Tullberg' s rat Rattus tullbergi

Pygmy mouse Mus musculoides

Spotted grass-mouse Lemniscomus striatus

Southern Nigerian hare Lepus zechi

Nigerian free-tailed bat Tadarida nigeriae

Yola free-tailed bat Tadarida websteri

Dark brown bat Scotophilus nigrita

Small dark bat Scotophilus nigritellus

White-winged bat Nycticeius albfuscus

Giant leaf-nosed bat Hipposideros gigas

Pox' s horse-shoe bat Rhinolophus foxi

Large-eared slit-faced bat Nycteris macrotis

Dwarf epaulet bat Epomophorus pus il lus

Pox's musk shrew Crocidura foxi

161 TABLE 31 Mammals recorded in the Guinea and Sudan Zones

Oribi Ourebia ourebio

Klipspringer Oreotragus oreotragus*

Roan antelope Hippo tragus equinus**

Nigerian reedbuck Redunca redunca nigeriensis

Grimm' s duiker Sylvicapra grimmia

Warthog Phacochoerus aethiopicus

Western dassie/hyrax Procavia ruficeps

Leopard Panthera pardus

Serval cat Felis serval

Spotted hyaena Crocuta crocuta

White-tailed mongoose Ichneumia albicauda

African civet Civettictis civetta

Cutting grass Thryonomys swinderianus

Senegal crested porcupine Hystrix cristata senegalica

Dalton's mouse Rattus daltoni

Graceful gerbil Taterillus gracilis gracilis***

Kemp's gerbil Tatera kempii

Red-legged ground squirrel Xerus erythropus eryihropus

Giant pangolin Manis gigantea**

Dog-faced baboon Papio anubis

Senegal galago Galago senegalensis senegalensis

Midge pipistrelle Pipistrellus Culex****

Variegated butterfly bat Chalinolubus variegata****

Thebes bat Nycteris thebaica

Common slit-face bat Nycteris his pi da

Egyptian fruit bat Rousettus aegyptiacus

Gambian fruit bat Epomophorus gambianus****

Mann' s musk shrew Crocidura mannii'

Giffard's musk shrew Crocidura giffardi

*' Mainly N. Guinea and the Sub-Sudan areas east of Bauchi. ** Widespread but seldom seen. ••* Primarily a Sudan species but occurs in the extreme north of the Guinea Zone. •*•* Mainly N. Guinea but occurs in the south of the Sudan Zone.

162 BISTORY by P Tuley

To give this subject adequate treatment is beyond the scope of this study. The project area is remarkably well documented and.has a long history of trans-Saharan contact with the Mediterranean littoral and trans-Sudanian contact with the Nile Valley and the Middle East. Posnett et al. (1971) devote a section of their Nigerian bibliography to this topic for those seeking further information. All that can be attempted here is a brief review of past events that are of some relevance to the present-day structures and land use.

In many ways the present administrative arrangements (Text Map 14) are a reflection of the history of the area. Bornu Province is the successor to the long-standing Bornu Kingdom. This Kingdom, itself once part of the even larger one of Kanem that encircled Lake Chad, has, allowing for the ebb and flow of conquest and defeat, stood as a coherent entity through the centuries approximating, on the western side of the lake, to the present boundaries.

To the westward a reasonably stable boundary has been maintained first with the great Sudan Kingdoms, then the Hausa States and the Pulani Emirates that followed. To the southward the depredations of the Jukun were eventually survived until the Jukun themselves fell before the Pulani advance. To the north the principal danger has been from Berber and Arab invasions and Zinder, in the past nominally a fief of Bornu, often proved a most troublesome vassal. Friction within the mother kingdom of Kanem and invasions from the area of the Nile Valley have troubled the land. One such invasion in the late nineteenth century, commanded by the Sudanese adventurer Rabeh, led to the defeat of the kingdom that had stood so long as a cultural unit. The advent of the European powers led to the defeat of Rabeh and their administrative boundaries during the colonial period closely followed the original struc tures, although Dikwa was separated from Bornu. In 1961, after a plebiscite organised by the united Nations, the northern area of the Cameroons under British mandate since the end of the 1914-18 World War, voted to- join Nigeria and is now part of the North-Eastern State.

Throughout the long span of history the pagan hill people in the south and east of the project area have survived the assaults and slave raids of successive cultures in the most remarkable fashion, relying on the rigours of the terrain to protect them against the advanced arms and cavalry of their foes. Some of these attained a fair degree of administra tive structure. Not all the southern groups were hill-dwellers. Some, largely of Jukun and Bantu origins, have occupied extensive lowland areas over many of which the later Pulani Emirs maintained only a tenuous hold. However, these groups and the hill people were extremely vulnerable at harvest time and often paid tribute to the Fulani to protect their crops. Loose confederations, such as the chieftancy system based on Hong, were a feature of these societies.

On the west and southwest a series of smaller emirates evolved as a 'buffer zone' between Bornu and the larger Fulani Emirates and a whole range of ethnic groups were able to resist complete assimilation by the major powers on either side. Thus today we see the project area, now representing the greater part of the North-Eastern State in the Federation of Nigeria, with the relict kingdom in the northeast, surrounded by a ring of small units, formerly lying between Bornu and the Fulani Empire or carved out of areas of Jukun/Bantu influence in the Gongola and Benue Valleys. However, among the hills, mountains and plateaux and to a lesser extent the lowlands, the tribal structure of many pagan or ex-pagan groups survives largely intact.

163 POPULATION by P Tuley

The distribution of population is shown in Text Map 12* and a table of population figures by administrative district is given in Volume 5. As can be seen from the map, excluding the major towns, the main centres of population lie in the foothills of the Mandara Range and the Yedseram Valley, the plains to the east and northeast of Maiduguri, the plains around Potiskum and the lower Gongola Valley. Although the density around Biu is to be expected, the continuation throughout the hilly basement areas around Gombi is notable. The broad location of the main ethnic groups is shown in Text Map 13, and many of the district names shown on Text Map 14 are indicative of tribal nomenclature.

Only a brief outline of the various ethnic groups is appropriate here. However the relation ship between cultural groupings and population pressures on the structure of present land use must not be overlooked. Ethnic considerations must also influence planning proposals and this subject receives further treatment in Volume 4. There is much interesting reading available, a bibliography of which is contained in Posnett et al. (1971).

The Kanuri

The Kanuri are the descendents of the original inhabitants of the Kanem and Bornu Kingdoms. Today they represent approximately half of the population of Bornu Province. The rural communities are typically mixed farmers, keeping a range of stock and raising arable crops.

The Shuwa Arabs

This small group of settled migrants originated in the Nile Valley. They are mostly found round the periphery of Lake Chad and in the Dikwa area, where they are often settled on sand islands among the clay plains of the area. They are also largely mixed farmers.

The Fulani The Fulani, of long standing in the project area, are associated with the emirates established at the conquest of the Jukun Empire. Therefore in centres such as Yola and Gombe are found Pulani dignitaries and a town-dwelling community, the Fulanen Gidda. The tradi tional Pulani (Bororoje) is however a nomadic pastoralist. Over the past few years there has been a steady influx of Pulani herdsmen, greatly adding to the number already in the project area, being driven from the north and northwest by the increasing arable acreages and the ploughing up of traditional dry season grazing areas for rice production.

The Hausa The Hausa are typically arable farmers. Primarily domiciled in the central plains in the north of Nigeria, their distribution impinges on the west of the project area. In addition there have been steady migratory movements by them into the major towns and other parts of the area, particularly the unoccupied heavy clay lands of the Gongola Valley.

* Based on the 1963 Population Census. Although outdated it still gives a useful visual picture of the concentrations of population.

164 Other Groups

In addition to the major well known groups, a multiplicity of tribal units are to be found. In the literature they are often grouped as 'pagan hill tribes'. While it is true that many of them have survived Pulani and other attacks by virtue of the defensive advantage offered by the upland areas, it should also be recognised that substantial tribal units have occupied lowlands or relatively accessible plateaux over the passage of years. Many of these have complex tribal histories of conquest and migration unrelated to the later struggles with the Pulani, and many Jukun and Bantu influences remain to this day. Traditional farming practices range from elaborate terracing to typical shifting cultivation.

165 COMMUNICATIONS by P Tuley

The major features of the communications system are shown in Text Map 15. As the project area has recently been the subject of a road development survey (Scott, Wilson, Kirkpatrick and Partners, 1964-9) little more need be added here. However the subject is dealt with under Agricultural Potential in Volume 4 and where appropriate under the land system descriptions in Volume 3. Two features merit special mention. In an area relatively well served with roads, the absence of adequate communication along the north bank of the Benue is a noticeable break in the network. The problems of keeping roads open during the rains on the black cracking clays should also be noted. This is of particular relevance to the international link between Maiduguri and Port Lamy in the Chad Republic.

Waterways The Benue is navigable as far as Yola for 4 months of the year and constitutes an important trade link with the delta ports and markets such as Onitsha. A considerable volume of produce from both Chad and Cameroon also passes to the world markets via this route. Plans for barrages on both the Benue and the Gongola could well improve this means of communica tion in future. Two motor ferries at Numan and Yola give access to the southern part of the North-Eastern State.

Air Travel There is a regular service linking the international airport at Kano with Maiduguri and Yola. In view of the distances involved there is every merit in the improvement of both light and routine commercial air services as an aid to development.

166 POPULATION DENSITY TEXT MAP 12 10'

MILES 0 25 I I I I I L

„ Main Road

H 1 I- Railway

* + + + + + + + International Boundary

_L 12° East of Greenwich 14" D.O.S.(LR.)3064Q Based on figures derived from the 1963 population census. Copyright reserved Drawn and photographed by Directorate of Overseas Surveys 1969. Printed by Ordnance Survey. ETHNIC GROUPS TEXT MAP 13 10* 12* 14° 1 1 s- \ 1 ^ |I4-

SCALE 1:3,000,000 \.* + *+*+ MILES 0 25 50 75 100 MILES ./

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Land over 1500 feet + + ••• + •+ __ International Boundary

i i 1 —Ip 10* 12° East of Greenwich 14*

D.O.S.(L.R.)30MX Drawn and photographed by Directorate of Overseas Surveys, 1970 Copyright reserved

169 ADMINISTRATIVE UNITS TEXT MAP 14

12°

BOUNDARIES

International __ + + ^ + + + + + + + + + State ^_._.^.^_ Provincial Divisional District

Hardawa 82 Girei 10° Yerima 83 Ribadu Darazo 84 Malabu Ganjua Dukku SARDAUNA PROVINCE Nafada 85 Kwami Belel Galenbi 06 Sorau Kirfi 8/ Maiha Ako 88 Mubi 89 Mayo Mbani Gom be Yamaltu 90 Michika Duguri 91 Madagali Fali 92 Gwoza Gwana West Tangale KANO PROVINCE 17 Rann Kalabalge 35 Askira Kaltungo 93 Birniwa 18 Potiskum 36 Shani Waja Longuda 94 Kaugama 1 Matsena 19 Fika Dadiya 95 Kirikasama 2 Nguru 20 Gujba BAUCHI PRC Kindiya 96 Gurri 9/ Auyo J Yusufari 21 Kaga ADAMAWA PROV 4 Borsari 22 Auno 37 Katagum 98 Kafin Hausa 5 Geidam Yerwa 38 Gamawa Muri 99 Bulangu A Mobber 2n4 Mafa 39 Sokwa Wurkum 100 Gwaram 7 Gubio 25 Konduga 40 Itas Bachama 8 Kanembu 2ft Gumsu 41 Udubo Longuda PLATEAU PROVINCE 9 Nganzie 27 Gulumba 42 Jamaare Shellem 01 Kanam 10 Mongonu 28 Margi 43 Madara Ga'anda 102 Wase ^WUKARI II Bedde 29 Bama 44 Shira KMba 103 Plain Yergam UJuJ 105 12 Fune 30 Woloji 45 Giade Uba 104 Resettlement CO 13 Damaturu 31 Babur 46 Chinade Mbula 14 Magumeri 17 Tera 47 Dambam Yungur BENUE PROVINCE lb Marte 11 West Bura 48 Dagaudu Song 16 Ngala 34 East Bura 49 Jalam Zummo 105 Kinda Kuvyo J_ 10° 12° East of Greenwich 14° D.O.S.(L.R.)3064S Based on N. Nigeria Administrative Area map, Provisional Edition, 1967. Drawn and photographed by Directorate of Overseas Surveys, 1969. Copyright reserved Printed by Ordnance Survey. COMMUNICATIONS TEXT MAP 15 10" 12' 14' 14" 14°

SCALE 1:3,000,000 25 50 75

. •*• • + •**,+ ••*•* + **•%*» 1/ \ 1/ ' \

.Mongonu \ S / \

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10° 12° East of Greenwich 14' D.O.S.(L.R.)3064W Drawn and photographed by Directorate of Overseas Surveys, 1970. © Copyright reserved

173 PART 3. REFERENCES

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WALOFF Z 1966 The upsurges and recessions of the Desert Locust plague. An historical survey. Anti-Locust Mem. No. 8.

WALTER M W 1967 Length of the rainy season in Nigeria. Niger. Geogr. J. 10, 123-126.

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ZONNEVELD I S 1970 The contribution of vegetation science to the exploration of natural resources. Wise Pap. Landbouwhogeschool Wageningen, No. 53, 31-44.

182 PUBLICATIONS OF THE LAND RESOURCES DIVISION These publications have a restricted distribution and are not available to booksellers. The Division makes a report on each completed project. The report is published as a Land Resource Study or Technical Bulletin only with the consent of the government concerned. The abbreviated titles of the reports in the style of the 'World List of Scientific Periodicals' are Land Resour. Stud, and Tech. Bull. Land Resour. Div. Overseas Dev. Admin.

BAWDEN N G and 1961 An aerial photographic reconnaissance of the present and LANGDALE-BROWN I possible land use in the Bamenda Area, Southern Cameroons.* BAWDEN M G and 1963 The land resources of Eastern Bechuanaland. STOBBS A R LANGDALE-BROWN I and 1963 The land use prospects of Northern Bechuanaland. SPOONER R J BAWDEN M G (Ed) 1965 Some soils of Northern Bechuanaland with a description of the main vegetation zones. LAND RESOURCE STUDIES

SPOONER R J and 1966 The development of the Lower Mgeta River Area of the JENKIN R N United Republic of Tanzania. Land Resource Study No. 1.

BAWDEN M G and 1966 The land resources of Southern Sardauna and Southern TULEY P Adamawa Provinces, Northern Nigeria. Land Resource Study No. 2.

BAWDEN M G and 1968 The land resources of Lesotho. Land Resource Study No. 3. CARROLL D M

JENKIN R N and 1968 An investigation of the coconut-growing potential of POALE M A Christmas Island. Volume 1, The environment and the plantations. Volume 2, Appendixes. Land Resource Study No. 4.

BLAIR RAINS A and 1968 The Northern State Lands, Botswana. Land Resource Study McKAY A D No. 5.

HILL I D 1969 An assessment of the possibilities of oil palm cultivation in Western Division, The Gambia. Land Resource Study No. 6

VERBOOM W C and 1970 An ecological survey of Western Province, Zambia, with BRUNT M A special reference to the fodder resources. Volume 1, The environment. Volume 2, The grasslands and their development. Land Resource Study No. 8.**

AITCHISON P J and 1970 The land resources of North East Nigeria. Volume 2, Tsetse GLOVER P E and Trypanosomiasis. Land Resource Study No. 9.

AITCHISON P J 1972 The land resources of North East Nigeria. Volume 1, BAWDEN M G The environment. Land Resource Study No. 9. CARROLL D M GLOVER P E KLINKENBERG K LEEUW P N DE and TULEY P

TECHNICAL BULLETINS

CARROLL D M and 1967 Notes on the soils of Lesotho. Technical Bulletin No. 1. BASCOMBE C L

PIGGOTT C J 1968 A soil survey of Seychelles. Technical Bulletin No. 2.

•Out of print. ••Land Resource Study No. 7 has not yet been published.

R 6019/8842/12 700 10/71 TP 183