the forest types of kenya

In: Pellikka, P., J. Ylhäisi & B. Clark (eds.) Taita Hills and Kenya, 2004 – seminar, reports and journal of a field excursion to Kenya. Expedition reports of the Department of Geography, University of Helsinki 40, 8-13. Helsinki 2004, ISBN 952-10-2077-6, 148 pp.

The forest types of Kenya

Piritta Peltorinne

Abstract Kenyan forests are biologically rich and harbour high concentrations of endemic species. Forests contain lowland rainforest in western Kenya, and montane forest in the central and western highlands and on higher hills and mountains. Forest classification done by describing dominant species and environmental features of different forest types summarises these forests in six main blocks: the volcanic mountains, the western plateau, the northern mountains, the coastal forests, the southern hills and the riverine forests. Since Kenyan forests are influenced by the farming and herding practices of the local inhabitants, many Kenyan forests are cultural rather than natural entities. However, they still support a forest cover of solely or mainly indigenous species. This is also why most forests are highly fragmented and under pressure – lowland forests are the first forests to be cleared for agriculture and present population pressure is making the forests more and more fragmented and degraded. Classification

In order to make any valid statements about Kenyan forests, I have to define the word first. What are forests? A continuous stand of trees at least 10 m tall, their canopy interlocking (Sayer et al. 1992:11). In FAO´s tropical forest assessment, forests were defined as vegetation types where trees cover more than 10 per cent of the land area (Rietbergen 1993:1). Different sources define forest in a very different way. In the tropics, different people mean different things by forest. In a present-day Western Europe, with its clear boundaries between farm and forest, terms no longer exist for forests that are farmed or grazed, or both. Many Kenyan forests are cultural rather than natural entities: They are influenced by the farming and herding practices of the local inhabitants, but still support a forest cover of solely or mainly indigenous species. The areas presented in Figure 1 are mosaics of relatively undisturbed, plus disturbed, forests and therefore it shows larger areas of forest than are suggested by some other sources. The limits of Kenyan forests are based on vegetation classification provided by F. White. Classification was published by Unesco and it was the result of 15 years of cooperation between Unesco and the Association pour l´Etude Taxonomique de la Flore de l´Afrigue Tropicale (AETFAT) (Sayer et al. 1992); although local conditions of exposure, geology, soil depth, mist frequency and seasonality of rainfall all lead to a finer

pattern of a community differentiation than White was able to portray. Kenyan forests Kenya covers an area of 582 646 km2, of which open waters cover 11 230 km2. 2008 km2 are covered by natural and exotic plantation forests, so the forest cover is 3.4% of the total land area and ~ 15% of the high potential land. Out of this, 1700 km2 represent indigenous forests, 122 km2 exotic plantation forests, 124 km2 privately owned forests and about 613 km2 mangrove forests (Ahmed & Mlay 1998:161). Kenya has the most diverse forests in East Africa, but they are highly fragmented. Forests contain lowland rain forest in western Kenya, and montane forest in the central and western highlands and on higher hills and mountains along the southern border. Many of these largest forested mountain blocks are of recent volcanic origin and are relatively species poor. The most widespread montane association are the moist Ocotea-Polyscias and drier Podocarpus-Cassipourea forests. Juniperus-Olea dominates the upper slopes. In addition, there are some coastal mosaic forests; some forests occur mainly in strips bordering rivers and some are fairly extensive mangroves along the coast, particularly at Lamu and at the mouth of the Tana River. Highest diversities are in the coastal forests, the western plateau forests such as Kakamega, and especially in the tiny,


geologically older mountains at the northern end of the Eastern Arc of block mountains – the Taita hills and Kasigau (Sayer et al. 1992:152). Out of these, only little scientific research relating directly to the northern mountains forests has been done, so they are mentioned here but not studied more closely. Forests can be summarised in six main blocks (see also Figure 1): 1. The high volcanic mountains and high ranges:

Elgon, Kenya, Aberdares, Cherangani and Mau 2. Western plateau: Kabarnet, Kakamega, Nandi,

Trans – Mara 3. Northern mountains: Ndotos, Mathews, Leroghi,

Kulal, Marsabit 4. Coastal forests: Arabuko – Sokoke, Tana,

Kayas, coral rag and mangrove forests 5. Southern hills: Taita Hills, Kasigau, Shimba

Hills, Chyulu Hills, Nguruman 6. Riverine forests: Tana and tributaries, Ewaso –

Ngiro, Kerio, Turkwell, Galana The high volcanic mountains and high ranges The volcanic mountains contain sub-montane forests: evergreen seasonal forests and evergreen forests (Figure 2). Deciduous species, e.g Calodendrum capense and Ekebergia capensis and the association of the Cassipourea malosana-Setaria plicatilis agg., are common in evergreen seasonal forests and the Cassipourea malosana-Popocarpus latifolius and the

Figure 1. The main forest types in Kenya.

Figure 2. Upper montane rain forest with bamboo on

the SE slope of Mt. Kenya (P. Pellikka). Cassipourea mallosana-Olea capensis ssp. hochstetteri communities in evergreen forests. The Aberdare Mountains are a broad mountain range located on the eastern side of the Gregory Rift Valley. They originated from uplift and warping, followed by volcanism and faulting, of the African basement from the early Tertiary to the Pleistocene. Characteristic to climate is the seasonal moisture regime: east of the Rift Valley the long rains last from March to May and are followed by a dry season from June to September. The short rains last from June to September and are followed by the short dry season, January to February. The annual rainfall in the Aberdares ranges from 940 to 3220 mm, and is maximal in the southeast. Low clouds and mist provide additional moisture. Mist is very common during the Gatano, the foggy period from July to August (Goldammer 1992:109). The Elgon Mountain forests contain Rapanea rhododendroides and Hagenia abyssinica. Mt. Kenya forests contain Hypericum keniense and Hypericum revolutum (Virtanen 1991). The Mau is the largest single block of forest in East Africa (Sayer et al. 1992:153). For the forests at Mt. Kenya, see Niemelä & Pellikka (2004). Western plateau Kakamega Forest is considered to be the easternmost outlier of the Guinea-Congolian forest. According to some resources (Virtanen 1991, Marttila & Virtanen 1998), it would be the only tropical rainforest remnant (35 km² area) in Kenya. Kagamega Forest has indigenous tree species such as Elgon teak, Red stinkwood Prunus africanum and African satinwood Zanthoxylum gillettii (Noad 1990).


Kakamega forest has unique plant species, e.g Aningeri altissima, Cordia millensii and Entandrophragma angolense. It also has unique animals, e.g L´Hoest´s monkey Cercopithecus Ihoesti , which only occurs in Kagamega forest, and two globally threatened bird species: Turner´s eremomela Eremomela turneri and Chapin´s flycatcher Muscicapa lendu (Sayer et al. 1992). According to Marttila (1998:82), Kakamega Forest is home to as many as 400 butterfly species. Coastal forests The coastal forests are considered to be the last refuges of an ancient forest mass that covered most of Central Africa between the Atlantic and the Indian Ocean. A long history of anthropogenic activity resulted in the patchy structure of small fragile forests, which is encountered today. The area’s climate is governed by the trade winds. The annual mean rainfall of about 1200 mm is mainly confined to the long rains between April and July and the short rains between October and December. January and February are considered arid. In addition to rainfall, a considerable amount of precipitation occurs in the form of fog and dewfall. Corresponding to the geological underground, some major types occur on the flat parts of coastal plateau – highly diverse Sterculia-Clorophora-Memecylon lowland rainforest, Clorophoro-Strychnatalia and Clorophora-lovoa forests. The coastal forests are diverse in wildlife as well. Two bird species are endemic in the Arabuko-Sokoke Forest: the Sokoke scops owl Otus ireneae and Clarke´s weaver Ploceus golandi. In addition, the forest has a number of endangered and rare animal species such as Golden rumped elephant shrew Rhynchocyon chrysopygus, the Sokoke bushytailed mongoose Bdeogale crassicauda omnivora and Ader´s duiker Cephalophus adersi, and six bird species are rare or threatened. Coral rag forests The coral rag coastal forests are dry, containing the margin Diani Forests. Typical species occurring there are, for example, Antiaris toxicaria, Milicia excelsa and Cussonia zimmermannii (Virtanen 1991). At a conference held in December 1997 in Tanzania, a

recommendation came out that the coastal forests be declared a World Heritage Site (Newmark 2002). The estuarine parts of the coast, where fresh water and seawater mix, are excellent habitat for mangrove forests. Traditionally protected Kaya forests The Kaya forests are relict patches of the once extensive and diverse Zanzibar-Inhambane lowland forests. During the 16th century, the Mijikenda people built defensive structures in these dense forests (the word Kaya means a homestead in several Bantu languages) to avoid the attacks of raiding Galla warriors. After the Mijikenda people moved out at the beginning of the 19th century, the Kayas became sacred sites because they contained the skulls and skeletal remains of ancestors. Forests are often on hilltops protecting water catchments and they are important in supporting a diverse flora, containing many rare plants and some medical plants. The Kaya forests have traditionally been protected by the tribal elders who use the old Kaya clearings for ceremonies (like initiation), but the breakdown in traditional beliefs and increase influence of Christianity and Islam along with the increasing demand for forest products is breaking this system down (Goldammer 1992, Sayer et al. 1992). Southern Hills The Taita Hills The Taita Hills mist forests are scattered forest fragments of different sizes, ranging from 200 ha to 1 ha (Figure 3). Based upon the measure-ments and estimates of the Tanzanian Ministry of Natural Resources and Tourism in 1996, which Newmark (2002) has updated, the total area of natural forest in Taita Hills is approximately six km². The area of closed forest – forest in which the canopy is generally intact and contiguous – is two km², and the area of open forest – forest in which the canopy is broken and non-contiguous – is four km². Approximately only 1.2 km² of land in Taita Hills is protected as forest reserve created through presidential declaration. The Taita Hills forest form the northernmost part of the Eastern Arc Mountains, a group of isolated mountains stretching from southeast Kenya through south central Tanzania (Figure


Figure 3. Indigenous mist forest on Vuria (2205 m)

in the Taita Hills (P. Pellikka). 5). The age and geologic origin of these mountains, the high rainfall and the moisture-laden southeast trade winds originating from the Indian Ocean have contributed to the very diverse and unique biota: the Eastern Arc mountains were recently classified one of the 25 world’s biodiversity hot-spots and the Taita Hills forests are a centre of endemism. Based on the IUCN risk criteria (red list of threatened animals) done in 1996, Taita Hills contains three critically endangered (rate of decline is 80% in 10 years) endemic bird species – Taita thrush Turdus helleri, Taita apalis Apalis (thoracica) fuscigularis and Taita white eye Zosterops (poliogaster) silvanus. Records also include an amphibian, Dickerson´s forest gecko Cnemaspis dickersonii, which is only found in Taita Hills and several endemic reptile species, e.g. the Taita reed frog Hyperolius viridiflavus and Amblyodipsas teitana. The Taita Hills forests are also home to several endemic plant species: Ceropegia verticilliata, Chassalia discolor ssp teitensis, Coffea fadenii, Impatiens engleri ssp. teitensis, Impatiens teitemsis ssp. Teitensis, Memecylon teitense, Psychotria petitii and Zimmermannia ovatoa and to one of the critically endangered African violet species, Saintpaulia teitensis (Sayer et al. 1992; Eastern Arc 2002). The Eastern Arc mountains and its forests are not only valuable for their biodiversity, but they also serve as catchments areas supplying fresh water to over 200 000 people (Eastern Arc 2002). Shimba Hills Shimba Hills are evergreen lowland forests. They contain endemic plants, like Dichapetalum fructuosum. Two endemic amphibians, Afrixallus Sylvaticus and Hyperolius rubrovermiculatus, are confined to the Shimba

Hills, which also house several restricted range species such as the black-and-rufous elephantshrew Rhynchocyon petersi, east coast akalat Sheppardia gunningi, and plain- backed and Uluguru violet-backed sunbirds Anthreptes reichenowi and Anthreptes neglectus. Riverine forests A narrow belt on the floodplain along the Tana River contains mainly evergreen forest. The extent of the forest depends on the water table, which subsides rapidly as one moves farther from the river. The width of the forests extends approximately 1-3 km on either side of the river (Kaarakka 1996). Lower Tana River forests have two endemic species: Tana River red colobus Procolobus rufomitratus rufomitratus and Tana River mangabey Cercobus galeritus galeritus (Sayer et al. 1992:153). In addition to Tana, other rivers also maintain riverine forests some of which are only very narrow belts on the riverside (Figure 4).

Figure 4. Riverine forest along Bura river in Taita

Taveta district (P. Pellikka). The state of the forests Most Kenyan forests are under pressure. That is because of deforestation, forest fragmentation, forest degradation, over-exploitation of species and the introduction of exotic species. One of the ecological communities that have been most extensively exploited is lowland forest, the first forests to be cleared for agriculture. Because the land best suited to the growth of forests is also good agricultural land, the remaining forests in Kenya are highly fragmented. Many species are inhibited from crossing forest gaps and therefore many isolated populations will not be “rescued” or supplemented by individuals


dispersing from forest fragments. Therefore, these species face additional risks of extinction. Deforestation and forest degradation can adversely affect many ecological processes impacting on e.g. soil-water relationship, but the over-exploitation of ecological resources for survival is a complex matter. The Kakamega Forest, for example, has suffered from continued overuse for timber, charcoal, firewood, cash crops and forest plantation. To counter such process, account must be taken of the characteristics of the biophysical environment, patterns of resource use and consumption, socio-cultural conditions and the socio-economic roots of poverty. A shift from commercial re-afforestation programmes to community involvement in forest resources development would have long-term benefits that are sustainable (Pahkasalo 2004). Social and farm forestry practices have emerged as possible sustainable solutions to environmental degradation, because these approaches favour

equity, ownership and desired community participation (Nummelin 1988, Kaarakka 1996, Kaarakka & Holmberg 1999, Odubho 2000, Newmark 2002). Summary Kenyan forests are biologically diverse, they contain numerous local endemic species and they are highly fragmented. Forests contain lowland rainforest in western Kenya, montane forest in the central and western highlands and on higher hills and mountains along the border. Some coastal forests are occurring in strips bordering rivers. The coastal forests, western plateau forests and the northern end of the Eastern Arc Mountains (Taita Hills) are most diverse. Because of recent and past population pressure, the remaining forest fragments are now quite small, scattered and becoming more and more fragmented and degraded.

Figure 5. The Taita Hills are the northernmost part of the Eastern Arc. Being the first barrier from the SE trade

winds, the hills gather clouds and maintain mist forests (P. Pellikka).


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89 p. Unpublished M.Sc. thesis, Department of Geography, University of Helsinki.

the forest types of kenya

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