The Aberdare or Nyandarua mountains are an isolated volcanic range that form the easternmost wall of the Gregory Rift Valley, to the east of the high Kinangop/Laikipia plateau. They are c.100 km long from north to south (the northern end almost reaching the equator). There are two main peaks, Ol Donyo Lesatima (3,999 m) to the north and Kinangop (3,906 m) to the south, separated by a long ‘saddle’ of land above 3,000 m. The small peak of Kipipiri (3,349 m) flanks the main range to the west, linked to it by a formerly forested valley at around 2,700 m. Deep ravines cut through the forested eastern and western flanks, and there are many clear streams and waterfalls. Mist and rain occur throughout much of the year, with precipitation varying from c.1,000 mm on the drier north-western slopes to as much as 3,000 mm in the south-east. The vegetation varies with altitude. A rich alpine and subalpine flora, including species of Senecio, Lobelia, Erica, Helichrysum and tussock grasses, gives way at c.3,000 m to bamboo Arundinaria alpina and then montane rainforest (mainly Juniperus procera-Podocarpus falcatus-Nuxia congesta forest on the western and north-western slopes, Ocotea forest on the south-east, andmixed Podocarpus latifolius forest on the east and on Kipipiri). Pockets of Hagenia forest occur in sheltered patches on the rolling moorland. The National Park lies mainly above the tree line, with some forest and scrub at lower altitudes in the so-called ‘salient’ near Nyeri. The Aberdares Forest Reserve (103,300 ha) occupies the lower slopes, in three main blocks that almost surround the park, with Kipipiri Forest Reserve (5,100 ha) tacked on to the east. The southern boundary of the Aberdares Forest Reserve adjoins the Kikuyu Escarpment forest (KE003) to the south. The Aberdares are an extremely important water catchment for the Tana river system, for the northern Ewaso Nyiro river and for Lake Naivasha, and provide much of the water supply for Nairobi and adjoining Districts.
See Box and Tables 2 and 3 for key species. Over 200 species have been recorded, including Aviceda cuculoides, Buteo oreophilus, Francolinus jacksoni, F. psilolaemus and Tauraco hartlaubi. Nectarinia johnstoni is found on the high peaks, foraging largely on lobelias, while other montane sunbirds (including Nectarinia tacazze, N. reichenowi, N. famosa and N. mediocris) are common at slightly lower altitudes. Macronyx sharpei is an uncommon resident of the southern slope grasslands, although like Cinnyricinclus femoralis and Euplectes jacksoni, its current status is uncertain. The restricted-range Cisticola aberdare occurs locally in the tussock moorland, with densities of around 3.2 birds/ha in suitable habitat; more than 20,000 pairs are estimated to occur. Regionally threatened species known from this site include Bostrychia olivacea (few records), Hieraaetus ayresii (scarce), Stephanoaetus coronatus (low density), Sarothrura affinis (rarely recorded), Porzana pusilla (uncommon), Tyto capensis (no recent records), Bubo capensis (local), and Euplectes progne (status uncertain).
Non-bird biodiversity: Globally threatened mammals include Diceros bicornis (CR) and Loxodonta africana (EN) (some 1,500 are resident), Tragelaphus eurycerus (LR/nt) occurs in the forest but sightings are on the decline, and Felis aurata, a rare species in Kenya, is also present. Endemic small mammals include Surdisorex norae (VU) and Tachyoryctes audax (VU). The snake Vipera hindii occurs only here and on Mount Kenya (IBA KE005), and the Aberdares hold several amphibians that are endemic to the central Kenyan highlands, including Hyperolius montanus, H. cystocandicans, Rana wittei and Phrynobatrachus kinangopensis. The butterfly Neptis kikuyuensis is endemic to forests in this IBA and on the Kikuyu Escarpment (KE003), and Charaxes nandina, endemic to central Kenya, has also been recorded. Notable plants include the Aberdare endemics Lobelia deckenii sattimae and Helichrysum gloria-dei, and the Aberdare/Mount Kenya endemics Lobelia bambuseti, Senecio keniensis, Senecio johnstonii battiscombei var. battiscombei and Senecio keniodendron. The Aberdares are rich in species of Alchemilla, including A. hageniae (endemic), A. argyrophylla (also on Mount Kenya), A. cyclophylla (also on Mount Kenya) and the rare A. microbetula (also on Mount Elgon).
Pressure/threats to key biodiversity
The Aberdare mountains IBA comprises 76,600 ha of National Park and 108,400 ha of Forest Reserve. The mountains are one of Kenya’s major water catchment areas, surrounded for the most part by intensive, small-scale agriculture. The high moorland is well protected and appears relatively safe, though the impact of frequent wildfires on Aberdare Cisticola populations needs further study. Habitat on the lower slopes, however, has been severely damaged in recent years. Forest destruction and degradation is the major threat to the site, through agricultural encroachment, illegal Cannabis sativa gardens, poaching of valuable trees and forest grazing of livestock. Forest-fires, either accidental or deliberately set (especially by honey collectors), have destroyed or damaged large tracts of forest during recent dry periods. Human–wildlife conflict has long been intense around the borders of the National Park ‘salient’ and the Forest Reserves. Marauding animals regularly damage crops, and occasionally kill or injure people. Parts of the ‘salient’ are already fenced, and there are plans to continue fencing sections of the Forest Reserves where problems are most severe. As in many of Kenya’s indigenous forests, management is presently inadequate, and is likely to remain so until an integrated management plan is supported by sufficient resources to put it into action. On the moorland, the status of Macronyx sharpei and Cisticola aberdare remains little known, and needs investigation. The unusual vegetation, rugged terrain, streams and waterfalls combine to create an area of great scenic beauty in the National Park, which has tremendous potential for ecotourism. This potential is only partially realised at present thanks to poor access roads and a lack of safe walking trails.