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This forest complex covers a substantial area of the south-western highlands of Kenya, and probably represents the largest remaining near-continuous block of montane indigenous forest in East Africa. The forests cloak the western slopes, and part of the crest, of the Mau Escarpment, a block of raised land that forms the western wall of the Gregory Rift Valley, rising steeply from the floor and sloping away more gradually to the west. There are five main Forest Reserves: Eastern, Western and South-western Mau (c.66,000, 22,700 and 84,000 ha respectively), Trans-Mara (34,400 ha) and Ol Pusimoru (17,200 ha). A sixth large block, the Maasai Mau (c.46,000 ha) is as yet ungazetted. In early 2001, a total of 59,134 ha (35,301 in Eastern Mau, 22,797 ha in South-western Mau, 713 ha in Western May and 1,03 ha in Western Mau) was designated for degazettement. The Mau has deep, fertile, volcanic soils, and rainfall in places is among the highest in Kenya. Annual precipitation ranges from c.1,000 mm in the east, with a seasonal regime, to 2,000 mm in the west, where it is more-or-less continuous around the year. Numerous streams drain the forests west of the scarp crest, forming part of the Sondu and Mara river systems, which flow into Lake Victoria, and the Southern Ewaso Ngiro system, which flows into Lake Natron. The Eastern Mau is the main watershed for Lake Nakuru, through the Njoro, Makalia and Enderit rivers. The surrounding areas are intensively farmed, with human population densities about twice as high on the western side of the forest as on the east. Vegetation patterns are complex, but there is a broad altitudinal zonation from west to east, lower montane forest below 2,300 m giving way to thickets of bamboo Arundinaria alpina mixed with forest and grassland, and finally to montane sclerophyllous forest near the escarpment crest. The lower montane forest is in best condition in the South-western Mau Nature Reserve, where characteristic trees include Aningeria adolfi-friedericii and Strombosia scheffleri. Elsewhere, this zone has been heavily and destructively logged, most recently for plywood from Polyscias kikuyuensis. Logged-over areas are dominated by pioneer species such as Tabernaemontana stapfiana, Syzygium guineense and Neoboutonia macrocalyx, while pockets of less-disturbed forest hold Olea capensis, Prunus africana, Albizia gummifera and Podocarpus latifolius. Substantial parts of the high Juniperus–Podocarpus–Olea forest have been encroached and cleared, although some sections remain in good condition. Large areas of both the Eastern and Western Mau have been converted to plantation forest.
See Box and Table 3 for key species. The avifauna of the forests (except for the Maasai Mau) is now fairly well studied. The Mau generally has a rich highland bird community, characteristic of the Central Kenya highlands but with some western affinities. A number of regional endemics occur such as Tauraco hartlaubi and the restricted-range Cisticola hunteri and Francolinus jacksoni. Regionally threatened species include Hieraaetus ayresii (scarce and local); Stephanoaetus coronatus (resident in small numbers); Tyto capensis (no recent records); Bubo capensis; Glaucidium tephronotum (fairly common); Indicator exilis; Sheppardia polioptera (uncommon and local); and Campephaga quiscalina (uncommon resident). This forest holds one of the richest examples of a central East African montane avifauna, and its size means that populations of most species are likely to be viable.
Non-bird biodiversity: Notable mammals include the rare Cephalophus silvicultor (LR/nt)), the little-known Felis aurata and the very sparsely distributed bat Stenonycteris lanosus. There appears to be a sizeable population of Loxodonta africana (EN) and what was once probably the largest Kenyan population of Tragelaphus eurycerus (LR/nt), now scarce. The butterfly Capys cupreus is endemic to the Mau Escarpment. There is little information on other fauna. With their relatively high rainfall, the Mau forests, and the South-west Mau in particular, are important for orchids. Three rare and unusual species occur in the South-west Mau. Polystachia bella, one of the few Kenyan endemic orchids, grows on the mossy branches of tall forest trees from 1,800–2,000 m in the Kericho area. Another endemic, Bulbophyllum bidenticulatum, is known from only two specimens collected along the Kiptiget river. Chaseella pseudohydra is a near-endemic recorded only from the South-west Mau and from Honde Gorge in Zimbabwe. The Mau is also one of the centres of abundance for the tree Polyscias kikuyuensis, endemic to central Kenya.
BirdLife International (2022) Important Bird Areas factsheet: Mau forest complex. Downloaded from http://www.birdlife.org on 01/12/2022.