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. JuniperusOlea 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,
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.
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 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
Figure 1. The main forest types in Kenya.
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).
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.
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 measurements 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
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.
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
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 moistureladen 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
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
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.
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).
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.
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