;~ ,_-•-^i»^rif»;.,*^^^*w'^^ Land Riic^ Scanned from original by ISRIC - World Soil Information, as ICSU World Data Centre for Soils. The purpose is to make a safe depository for endangered documents and to make the accrued Information available for consultation, following Fair Use Suidelines. Every effort is taken to respect Copyright of the materials within the archives where the identification of the Copyright holder is clear and, where feasible, to contact the originators. For questions please contact soil.isric(a>wur.nl indicating the item reference number concerned. Land resources of the Solomon Islands Volume 5 Santa Isabel I4 2.I& View over Bahana Passage, north-east Santa Isabel, towards Barora Fa Island. Lowland forest covers the hills in the background and forms islands surrounded by mangrove forest in the middle distance. Land Resources Division Land resources of the Solomon Islands Volume 5 Santa Isabel J R F Hansell and J R D Wall Land Resource Study 18 Land Resources Division, Ministry of Overseas Development Tolworth Tower, Surbiton, Surrey, England KT6 7DY 1976 THE LAND RESOURCES DIVISION The Land Resources Division of the Ministry of Overseas Development 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 overseas 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. IV List of volumes Title: Land resources of the Solomon Islands, J R F Hansell and J R D Wall. Volume 1 Introduction and recommendations Volume 2 Guadalcanal and the Florida Islands Volume 3 Malaita and Ulawa Volume 4 New Georgia Group and the Russell Islands Volume 5 Santa Isabel Volume 6 Choiseul and theShortland Islands Volume 7 San Cristobal and adjacent islands Volume 8 Outer Islands v Contents LIST OF FIGURES x LIST OF PLATES x LIST OF STEREOPAIRS x LIST OF TEXT MAPS xj LIST OF SEPARATE MAPS XI PART1. INTRODUCTION 1 Preface 1 Abstract 1 Résumé 1 Descriptors for co-ordinate indexing 2 PART 2. THE ENVIRONMENT 3 Introduction 3 Factors in the determination of potential land use 3 Environmental factors 3 Location 4 Physiographic regions 4 I San Jorge-Saikile area 4 II Mbughotu peninsula 4 III Jajao-Hograno foothills 5 IV East-central mountains and ridges 6 V Maringe-Gao hills and ridges 7 VI Ghadanga foothills 7 VII Rakata ridges and hills 7 vii V111 West-central ridges and plateaux 8 IX Allardyce ridges and foothills 8 X Western islands 8 Landforms 9 High, long ridges 9 Uneven ridges 10 Ridge and hill areas 10 Rounded hills and ridges 15 Low, long ridges 15 Low, short ridges 16 Long, radial ridges 16 Karst 16 Plateaux and cuestas 25 Terraces 25 Fluvial plains 26 Swamps 26 Littoral landforms 27 Soils 27 Introduction 27 Organic soils with mostly well-decomposed peat (Histosols: Hemists) 30 Young soils with little or no horizon development (Entisols: Aquents, Psamments, Orthents, Fluvents) 30 Slightly weathered soils with little horizon development (Inceptisols: Tropepts) 32 Moderately to strongly weathered and leached soils with high base status (Alfisols: Udalfs) 37 Moderately weathered soils with thick dark topsoil and high base status (Mollisols: Rendolls, Udolls) 38 Strongly weathered and leached soils with low base status (Ultisols: Humults, Udults) 38 Very strongly weathered and leached soils (Oxisols: Humox, Orthox) 40 Current Land Use 41 Introduction 41 Shifting cultivation 43 Cash crops 43 Coconuts 43 Cocoa 44 Other crops 44 Cattle 45 Land use pattern 45 Forests 48 PART 3. LANDSCAPE ANALYSIS: LAND REGIONS AND LAND SYSTEMS 51 Introduction 51 Wairaha Land Region 52 1. Tolombusu Ghausava Land Region 54 2. Marapa, 3. Mbina, 4. Tadai, 5. Tohebakala Kaipito Land Region 62 6. Jajao, 7. Mablosi, 8. Madagha, 9. Zabana Manawai Land Region 70 10. Andi, 11.Boinio, 12. Henefau, 13. Ukima'au viii Kwainangali Land Region 78 14. Fata'olo, 15. Tamba'a Mbelaha Land Region 82 16. Allardyce, 17. Beamalalu, 18. Eghueghu, 19. Ma'ariki, 20.- Nanamihi Rokera Land Region 92 21. Malu'u Fiu Land Region 94 22. Kumotu, 23. Litoghahira, 24. Lomousa, 25. Pusuraghi, 26. Tenaru PART 4. AGRICULTURAL POTENTIAL OF THE LAND REGIONS 105 Introduction 105 Wairaha and Kaipito Land Regions 106 Ghausava Land Region 108 Manawai Land Region 108 Kwainangali Land Region 110 Mbelaha Land Region 112 Rokera Land Region 113 Fiu Land Region 113 PART 5. MINOR DEVELOPMENT AREAS 117 Introduction 117 Kilokaka 118 _ Susubona 119 Kaipito 120 Kosisi 121 Titiligama 122 Other developable areas 123 PART 6. REFERENCES AND RELEVANT WORKS 125 APPENDIXES 1 Selected Soil Profile Descriptions 129 2 Definition of Geomorphological Parameters 157 3 Soil Analysis Methodsand Definition of Pedological Parameters 163 IX LIST OF FIGURES 5-1 Cross-section of Santa Isabel and San Jorge showing inferred relationships between land systems, geology and landforms 13 5-2 Diagrammatic cross-section from Maringe lagoon to the south-west showing lithology/landform/soil/vegetation/land use relationships 34 5-3 Diagrammatic cross-section near Allardyce Harbour showing lithology/landform/soil/vegetation/land use relationships 34 5-4 Diagrammatic cross-section north-east from the Kaipito River showing lithology/landform/soil/vegetation and land use relationships 35 5-5 Diagrammatic cross-section from Kia to the north showing lithology/landform/soil/vegetation/land use relationships 35 5-6 Changes of soil properties with depth in selected Santa Isabel profiles 36 LIST OF PLATES Frontispiece View over Bahana Passage, north-east Santa Isabel, towards Barora Fa Island. Lowland forest covers the hills in the background and forms islands surrounded by mangrove forest in the middle distance ii 5-1 The Mbina Land System at Kolosuri, south-west Santa Isabel. Casuarina papuana dominates the lowland forest 109 5-2 A road cutting exposes the shallow soils of the Mbina Land System, Kolosuri 109 5-3 The abrupt interface between soil and parent material in Dystropepts and Troporthents of the Mbina Land System, Kolosuri 109 LIST OF STEREOPAIRS 5-1 A forested area showing limestone karst of the Henefau Land System and various forms of ridges over basaltic and ultramafic rocks 17 5-2 An uninhabited area of coastal swamps, low hills with accordant summits and basaltic ridges separated by the Korighole - Kaipito major fault line 18 5-3 An area containing ultramafic rocks of the Mbina Land System and soils with high nickel content 19 5-4 A stereotriplet covering the Ortega Channel showing lowland plains, hills of basaltic and metamorphic rock, low terraces and ridges derived from serpentinous sediments, freshwater swamps and a cultivated alluvial area in the Kaipito Valley 20 5-5 An area of low rdiges with accordant summits, derived from areanaceous sediments in the south and basaltic volcanics in the north 21 x 5-6 An area of lime-rich sediments forming low hills, ridges and platforms 5-7 An unused area of basaltic volcanics and limestone underlying high, narrow ridges, and arenaceous sediments forming plateaux and hills 5-8 An area of basalt-based ridges and sandy cuestas in the north-central watershed, to the north of which are limestone ridge karst and younger ridges of fine-grained calcareous sediments LIST OF TEXT MAPS 13 Study area location 14 Landforms LIST OF SEPARATE MAPS (in carton) 5a Physiography and physiographic regions 5b Catchment areas 5c Soil sample sites and traverses 5d Soil associations 5e Land systems and land regions 5f Land use, 1962-72 5g Agricultural opportunity areas 5h Forest types XI Parts 1-6 Part 1 Introduction PREFACE Volume 5 covers Santa Isabel, San Jorge, the small outlying island of Ramos and the Arnavon Islands in the Manning Strait. It is one of a series of volumes describing the land resources of the Solomon Islands. Each volume is concerned with a major island or island group and incorporates the results of fieldwork, the subsequent land classification and the assessment of its agricultural potential. Reports are issued oh an island-by-island basis to simplify district planning and to facilitate'access to the recommendations. Landforms and soils are described fully in this volume as together they form the basis of the land classification, but other aspects of the physical environment such as geology, climate and vegetation are given only cursory attention having been described more fully in Volume 1. Similarly, aspects of the cultural environment are only discussed in this volume where they are unique to Santa Isabel and a fuller discussion of population and subsistence agriculture, for example, can be found in Volume 1. With this method of presentation unnecessary repetition is avoided, and it is possible to separate primary information gathered during the fieldwork from information derived largely from already published material. The system of measurement used in the report is metric. Parallel versions in imperial units are given of tabulated areal data only where they deal with opportunity areas. ABSTRACT Santa Isabel and nearby small islands occupy approximately 4122 km^. The area has been studied on a reconnaissance basis and the physiography, landforms, soils, forest types and present land use are mapped and described. There are eight land regions subdivided into 26 land systems, in each of which component facets are described in detail with areal measurements. The agricultural potential of the land regions is discussed and five minor development areas are mapped having a large proportion of land suitable for large-scale, cash-crop agriculture, and together totalling 89 km^.