JOURNAL OF THE EAST AFRICA NATURAL HISTORY SOCIETY AND NATIONAL MUSEUM 20th November, 1975 No. 154 TIlE VASCULAR PLANTS OF MERU NATIONAL PARK, KENYA Part I. A preliminary survey of the vegetation By J. G. AMENT Rua Barao do Bananal965, Vila Pompeia, Sao Paulo 05024, Capital. Brasil This study was made at the request of Mr Peter Jenkins, Warden of Meru National Park, and has been fully supported by Dr. Perez Olindo, Director of Kenya National Parks. Mr Peter Ordway provided the funds for the major part of the field work. The Mriean Wildlife Leadership Foundation financed a second period of field work and the publication. My thanks are also due to Dr. P. J. Greenway and Mr J. B. Gillett of the East Mrican Herbarium for their help and encouragement throughout; Mr Gillett has put in a great deal of work on the checklist and visited the camp in Meru National Park for a short period. Miss Kabuye, Botanist-in-Charge of the East Mrican Herbarium, made available drying paper for the specimens and the invaluable services of Mr Frank Magogo, who helped me with most of the collecting and was an excellent field assistant. All the identifi• cations were carried out at the East Mrican Herbarium and I am most grateful to the members of staff involved. I am also indebted to Mr Edward Potter who did a useful pre-preliminary survey of the park vegetation, and to Mr R. Welch who introduced me to this type of work. I have tried to be influenced as much as possible by Dr. P. J. Greenway's work; I have based my vegetation types on his A classification of B.A. Rangeland with an appendix on terminology (D. J. Pratt, P. J. Greenway and M. D. Gwynne-I966). Drs. P. Cooper and P. Larkin of the National Agricultural Research Station at Kitale were kind enough to arrange for a pasture value analysis of my grass samples, done by Mr A. W. Bristow. I am publishing their results and comments, but unfortu• nately have not been able to follow this work up with observations of pasture utilization by game animals etc. I hope the results may prove of interest to future workers in the area. The soil pH readings were taken with a soil pH kit made available by the Coffee Research Station, Ruiru. Page 2 LOCATION AND CLIMATE Meru National Park lies on the Equator between 0°20' north and 0°10' south, 38°0' and 38°25' east of Greenwich. The park is roughly triangular (see map I), 31'£ 31'£ .'£ ""E I'N MERU NATIONAL PARK and surrounds ~MtN Nallonal Park from series 1111 Kenya and Uganda • e••.••Tula l!!1.and •••• '10 m. O' 1'5 Map 1 The Nyambeni hills, some 10 miles (IS,S kIn) north-west of the park, rise to 8,000 ft, (2500 m) above sea level (A,S.L.), Along the west boundary of the park the land rises to slightly over 2800 ft. (850 m) A.S.L, and from this point there is a steadily descending gradient across the park from north-west to south-east, The south-eastern comer, where the Tana River forms the park boundary for about 10 miles (15.5 kIn), is about 1,000 ft, (300 m) A.S.L, This is the driest and hottest area in the park; the annual rainfall figures follow the altitude gradient across the park and the temperature gradient is inversely proportional to it, The rainfall at park HQ for the 12 years 1963-1974 is shown in table I, Note• worthy is the great variability, the maximum annual rainfall being more than four Table 1 Annual rainfall at Meru Park HQ Year Inches mm Year Inches mm 1963 33·9 860 1968 52.6 1337 1964 19.6 497 1969 28·9 734 1965 14·1 357 1970 16.2 411 1966 26.1 663 1971 21.4 543 1967 53.6 1362 Average 29·7 754 Addendum The rainfall at Park HQ for 1972-4has been as foUows Year Inches mm 1972 21.2 538 1973 11.3 287 1974 21. 1 536 av, 1963-1974 28.5 in 724 Page 3 times as great as the minimum. The average, 724 mIn, is probably higher than the true average for a much longer period. The distribution of rain over the year is shown by figure I, showing that the 'short rains' in November are much more intense than the 'long rains' in March-May. The longest recorded drought is 4.5 months. >'0 -o ~ "F".·A"M"J-J"A Fig. I Rain fall, in inches o=Dry Month, 0 rainfall. 2=Less than 2 (scms) rainfall. 10=More than 10 (2ScmS) rainfall. The park is well watered by rivers rising in the Nyambenis and flowing across it in a'south-easterly direction to join the Tana River (see map 2). Most of those north of the Kiolu River carry water throughout the dry season; the Kiolu and its tributaries dry out, the Ura and Tana rivers providing the only permanent water in the southern section of the park. Rive ••••••••••••••••••••••••••• --L.. Cont.our. In 1Mtr ••••••••••• Ali~ Hili•••••••••••••••••••••••••••••• 0: Notional Park Boundary,••••_. __ o 5 10 Kllom.tree I 1 I MERU NATIONAL PARK _ Rivers Map 2 Page 4 During the drier months the game collects in the swamps in the northern part of the park, moving to the riverine thicket should the swamps dry out. Shortly after the first rain many of the animals move into the southern section. In recent years the grasslands have been bumt from time to time. The policy has been to burn early, to prevent hotter more extensive fires later in the dry season. This has probably helped preserve the 'lightly wooded grasslands' in the northern part of the park. GEOLOGY Geologically, Meru National Park can be conveniently divided into two sections (see map 3). The northern part of the park is formed of Pleistocene-Recent lava, which flowed from volcanos which formed the Nyambeni ridge. In the southern part of the park the Precambrian rock of the basement system is exposed. The lava from the Nyambeni volcanic activity flowed along the pre-existing river valleys, blocking the watercourses. This caused the rivers to flow along the parallel edges of the tongue-shaped lava flows, tributaries uniting round the tongue points. This formation can be seen near the north-west boundary of the park, where the Kindani and Rojewero rivers unite. The lava is chiefly olivine basalt. In the north-west part of the park lava strewn ridges of powdery grey to grey-brown soil slope gently upwards-towards the Nyambenis. In the river valleys are swamps of varying width and the soil is grey to black. East of the 38°10' meridian the land flattens somewhat and grey volcanic alluvial soils mark the site of Pleistocene lake beds. The swamps bordering the watercourses are wider and between them are flat areas of powdery grey alkaline soil and low lava strewn ridges. There is an area of fossiliferous limestone on the banks of the Rojewero River, as it approaches confluence with the Murera (see map 3). This has been formed in the bed ofa lake formed when the river was dammed by a lava flow; it post-dates the Nyambeni lava flows. The freshwater Gastropod fossils which have been examined give no indica• tion of the age of the beds, as the forms present were extant over too long a period (Miocene to Recent). North-east of the Murera River, which forms most of the eastern boundary of the park, red sandy soil covers the basement rocks. A strip of this soil lies inside the park along the south-west bank of the river north of its confluence with the Rojewero. The southern edge of the Pleistocene lava flows is approximately marked by the courses of the Kiolu and Rojewero rivers. South of these rivers the metamorphic rocks of the basement system are exposed. The area is dissected by incised stream courses and the meandering course of the more mature Kiolu River. Across the south-west boundary of the park Pleistocene lava flows form ridges between the rivers, and cover the biotite gneiss of the basement system. There is a small area of volcanic alluvial soil stretching from the Ura gate to a point some 10 km due north, and a small lacustrine deposit of fossiliferous limestone near the west boundary (see map 3). At Ntoe Ndogo the biotite gneiss is exposed and the red soil derived from it covers the area eastwards to the 38°12' meridian. It is interrupted by several north-south running strips of quartz-felspar hornblende gneiss and from this harder rock are formed the rocky inselbergs which are characteristic of the southern part of the park. East of the 38"12' meridian the homeblende migmatite, rather harder than the biotin: gneiss, gives a red, shallow, sandy soil. .•• f\ombtend. gneis5e1i '.~; 8ietite 9M1Hft . -.' Vokanic & vDlcanic alluvial soits Horlibl.nd. migmatl t. Fossitif'ro"s timestonl' .1QuortZ."ISpAl. gneiS.Ses & C-,·Olivine basaUs lIewlll 18"20'£ I ______ {_O'IO'N ,I I f • I I • I I I MERU NATIONAL PARK _ Geological features Map 3 VEGETATION The vegetation can be divided into three main types, the boundaries of which correspond closely with the geological divisions (see maps 3 and 4). The section south of the division followed by the west part of the Kiolu River and the east part of the Rojewero River carries AcaciafCommiphora bushland wherever the basement rock is exposed.