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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, 14-20. Helsinki 2004, ISBN 952-10-2077-6, 148 pp.
Zonation and characteristics of the vegetation of Mt. Kenya
Tuomo Niemelä1 & Petri Pellikka2
Botanical Museum1 and Department of Geography2, University of Helsinki
Abstract
In this paper the vegetation of Mt. Kenya is briefly summarized, mostly by describing the zonation from the
foothills upwards: Montane rain forests, Bamboo zone, Upper montane forest, Ericaceous zone, Páramo, and
Nival zone. The peculiar giant rosette plants of the upper zones and their ecology are outlined. Mt. Kenya
belongs to the series of volcanoes that occur along the fault lines of the Rift Valley system; they are fairly
young (a few millions of years) if compared to the ancient Eastern Arc mountains closer to the Indian Ocean
coastline, whose origins date back to 20 my or more.
Introduction
The predominantly gentle East African terrain is
here and there interrupted by isolated
mountains. They are of two origins.
Closer to the eastern coastline are ancient
mountains of the Eastern Arc: Taita Hills in
Kenya, and in Tanzania within sight distance
the Pare and Usambara Mountains, and several
others further south. The faulting and upheaval
of these granitic mountains commenced in the
Miocene some 20 million years (my) ago or
earlier still, and their forests are remnants of the
Pan-African tropical forest belt that covered
equatorial Africa from the Atlantic coast to the
Indian Ocean before the formation of the upland
and gorge system of the Rift Valley. Eastern
Arc forests are characterized by a very high
degree of endemism, harbouring endemic tree
species and even genera. For the most part,
these forests lie well below the altitude of 2000
metres, with the foothills just a few hundred
metres above sea level.
Along the Rift Valley fault lines there are
volcanoes, some of them being active, like
Oldoinyo Lengai in northwestern Tanzania (a
major eruption in mid-1960s), or dormant, like
Kilimanjaro and Mt. Meru 70 km west of it, or
extinct, like Mt. Kenya. As compared to the
Eastern Arc mountains, these volcanoes are
fairly young: the first lavas of Kilimanjaro 1
my, Ngorongoro 2.5 my and Mt. Kenya 3 my
old. Their age explains the lower degree of
endemism if compared to Eastern Arc. On the
other hand, their foothills lie at the altitude of
1500 to 2000 m above sea level and peaks of
many of them exceed 5000 m. High altitude
makes these volcanoes characteristic in their
vegetation, and altitudinal zonation is seen
clearly on their slopes.
Even though general features are the same, East
African volcanoes differ from each other in
many details of their vegetation. This is
explained partly by their different ages, and
anomalies in rainfall, but also by the distances
from one mountain to the next, and hence the
degree of isolation, or probability of seed
exchange. The higher up we go, the more
specialized vegetation we encounter.
The vegetation zones are not similar on each
slope of the mountain. Since eastern and
southern slopes receive more rainfall than the
other slopes, the lower montane zone reaches
lower there than on the other slopes. In addition,
there is no bamboo zone on the northern slope
(Figure 1). The vegetation zones are also
modified by human interference. The lower
montane forest is taken for cultivation in the
lower elevations. This has been distinguished on
a Landsat TM satellite scene. There is a sharp
edge between forest and cultivations in each
slope of the massif (Figure 2). The Landsat
MSS satellite scene from 1976 reveals that the
upper montane forest was a continuous belt
around Mt. Kenya. As the northern slope is
lacking a bamboo zone, the agricultural fields
are nowadays practically next to upper
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, 14-20. Helsinki 2004, ISBN 952-10-2077-6, 148 pp.
Figure 1. The vegetation zones of Mt. Kenya, according to Coe (1967), strongly modified.
Figure 2. The vegetation zones around Mt. Kenya interpreted from Landsat TM satellite scenes from 1976 and
the 1990s. The bamboo zone in the west is patchy and zone limits are not as clear than in the east.
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, 14-20. Helsinki 2004, ISBN 952-10-2077-6, 148 pp.
Figure 3. Bamboo thicket on the SW-slope of Mt. Kenya (P. Pellikka).
montane forest. This zone is very favourable for
wheat cultivation, for example. In addition, the
forest reached lower elevations during the 1970s
and did not form such a sharp border with
cultivated land. The upper montane forest zone
and the ericaceous zone are affected by humans
as well. The forest and grassland ARE burned in
order to favour growth of flowering plants for
bees and honey making.
Montane rain forest of Mt. Kenya
The foothills of Mt. Kenya are (or at least were
originally) covered by dense evergreen forests,
extending from about 2200 to 3500 metres.
Their lowermost section, the Lower montane
forests, also called Montane rain forests, are
very similar in structure and general appearance
to the lowland rain forests of the Congo basin.
At the species level, however, they are different:
even though a few tree genera are the same,
lowland rain forests and montane forests do not
share common species. This is mostly due to
cooler climate in upland areas, even though
there are no frosts in the montane rainforest
belt.
Montane rain forests are the most luxuriant ones
in the country. The trees of the upper canopy are
30–40 metres tall, with heavy-branched and
wide-spreading crowns, and very thick and
pole-shaped trunks, often supported by
buttresses. The forest structure is layered:
beneath the emergents there are trees of middle
stratum, 15–30 m tall, which are more shadetolerant and have narrower crowns. Smaller
trees make a lower canopy, but shrubs are few,
and the herb layer is usually sparse, except
along roadsides where there is more light.
Lianes and strangling figs abound, and
epiphytes make thick and speciose colonies on
the branches of larger trees.
The wealth of forest vegetation in this zone is
maintained by abundant rainfall, 1500–2500
mm per annum depending on the exposure of
the slopes, by frequent mists, and rich volcanic
soil. However, there is a dry season of a few
months. Some of the emergent trees shed their
leaves for a short time, but the forest as a whole
is evergreen.
These forests have harboured many valuable
timber trees, and in most areas they have been
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, 14-20. Helsinki 2004, ISBN 952-10-2077-6, 148 pp.
heavily logged in the past. Also, along our
ascent of the mountain via the eastern slope, the
forest structure was obviously disturbed:
emergent trees were much fewer than in a
natural state. Anyhow, we saw, for instance,
giant-size examples of East African camphor
(Ocotea usambarensis), Wild olive (Olea
capensis), and, on drier slopes and further up,
the coniferous trees Podo (Podocarpus falcatus)
and East African cedar (Juniperus procera).
The high rainfall, luxuriant and complex
vegetation, and the abundance of mossy and
other epiphytes make montane rain forests very
important catchment areas. Water is effectively
absorbed in the vegetation, peatlands, and
humid soil, and runoff is even throughout the
year. Therefore, and in order to avoid soil
erosion, the protection of these forests is of
paramount importance.
Bamboo zone
Above the montane rain forests there is a
speciality of tropical African mountains, the
Bamboo zone. While it is fragmentary on some
mountains, like Mt. Kilimanjaro and Meru, it is
spectacularly well developed on Mt. Kenya.
Climbing uphill, the forests end quite abruptly,
and the landscape changes into a uniform
thicket of Mountain bamboo (Arundinaria
alpina). The stands of bamboo culms are so
dense that passage is only possible along roads
and elephant paths (Figure 3). Tree seedlings
usually succumb to the lack of light.
Bamboo thickets make a sickle-shaped belt on
the moister eastern, southeastern and southern
sides of the mountain, while the plant is almost
absent from the drier northwestern slope. The
zone is several kilometres wide at an altitude of
2200–3200 metres a.s.l. The plant needs, in
addition to plentiful rains, also rich and deep
soil and fairly gentle terrain.
Mountain bamboo is a perennial grass, over 10
m tall, and its 3–7 cm thick culms arise from
massive rootstocks. This species is endemic to
the East African mountains. New shoots
develop almost continuously from the rootstock,
while older ones die but stay standing for many
years. No flowers develop, however, until the
bamboo population reaches the age of 7–9 years
(on some mountains 15 years or even 30 years
in
Uganda).
Then
flowering
starts
simultaneously in areas of several hectares: all
the plants burst into flowers, shed the seeds, and
die. A new generation of bamboo develops from
seedlings. The few trees found amongst bamboo
originate from such periods when the bamboo
vegetation temporarily disappears, and enough
light is available close to the ground. It is not
known what triggers the simultaneous flowering, but it is understandable that a strict rhythm
has developed: bamboo individuals with erratic
flowering cycle would have no possibilities to
produce viable seedlings in the deep shadow of
mature bamboo vegetation.
Upper montane forest
Higher up, above the bamboo zone, there are
still forests. Even if a few tree species of the
montane rainforest zone reach so high up – for
instance East African cedar (Juniperus procera)
– the high altitude Upper montane forests are
different in their characteristics and most of the
tree species.
Trees are mostly low, 12–20 metres tall, and
their trunks are twisted and repeatedly
branched, with cupola-shaped crowns. Even
though the tree stands may be fairly dense, the
forest structure is not layered, and enough light
reaches ground level for a thick grass and herb
vegetation to develop (Figure 4). The so-called
Elephant grass (Eleusine jaegeri) is a common,
robust plant growing in big tussocks. Forests
often have a park-like appearance. Rainfall up
here at the altitude of 2500–3500 metres is
lower than in the montane rainforest zone, but
also evaporation is smaller, and frequent heavy
mists contribute to the humidity. Hence the
upper montane forests are often called Cloud
forests or Mist forests.
Along the trail from Mt. Kenya Bandas upward
we saw the tree-like Giant St. John’s wort (Hpericum revolutum) with large yellow flowers;
it is common in all East African mountains high
enough to maintain this forest zone. Robust
Kosso trees (Hagenia abyssinica, Rosaceae; in
Kikuyu Muthithiku) were plentiful around the
Mt. Kenya Bandas and along the path upwards,
growing together with single thick East African
cedars.
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, 14-20. Helsinki 2004, ISBN 952-10-2077-6, 148 pp.
Figure 4. In the upper montane zone the trees are twisted and multi-stemmed and lichen epiphytes are abundant
and conspicuous (P. Pellikka).
Ericaceous zone
True forests end approximately at the altitude
where night frosts become frequent, ca. 3500
metres a.s.l. Above this, the Ericaceous zone
starts (Figure 5). The demarcation between
forest and Erica heath is abrupt, but it does not
make a straight line: because of the hilly nature
of the slopes of Mt. Kenya, the transition is
mosaic-like, forests growing in shaded valleys,
and Erica heathland on exposed slopes, until,
further up, forests end completely.
The zone is named according to Giant heather
(Erica arborea, also other Erica species), a
woody erect shrub, half-metre tall on dry and
upper slopes but 1–2 metres tall throughout
most of the zone. It has scaly leaves of springgreen colour, and little, pink, urn-shaped
flowers. Erica and Muhatu (in Kikuyu; Stoebe
kilimandscharica) with a pastel colour of bluish
green, make an almost continuous heathland as
far as can be seen (Figure 5). Sugar bush
(Protea kilimandscharica) is similar in size, but
it has larger ovate leaves and striking, large,
pale yellow flowers (in fact capitulum
inflorescences). Among these woody shrubs
there is a plenty of lilies and other herbs with
bright coloured flowers.
The Heather family (Ericaceae) seems to have a
Laurasian origin, and could spread from the
Mediterranean to eastern and southern Africa
along mountain chains after the continents
touched some 18 my ago. It became extremely
speciose in South Africa. The Protea family
(Proteaceae) is a typical East Gondwana
element, common in South Africa and also
Australia (for instance Silver oak, Grevillea
robusta, cultivated in Kenya) and neighbouring
islands.
The ericaceous zone is very well developed on
the eastern slope of Mt. Kenya. In its upper
limit the shrubs remain lower and more spaced.
The areas in between are occupied by tussock
grasses and bright-flowered dwarf shrubs,
characteristic of the next altitudinal belt. This
transition is caused by ever more frequent and
severe night frosts, and the rapid decline in
rainfall at the altitude of ca. 4000 metres.
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, 14-20. Helsinki 2004, ISBN 952-10-2077-6, 148 pp.
Páramo
The term Páramo is favoured by most plant
geographers working in the tropics; the more
colloquial term ‘Alpine zone’ is often used but
not recommended as it refers to the Alps of
Europe. Páramo starts from the transition of the
ericaceous zone ca. 4000 m a.s.l, and its upper
limit is somewhere at 4800–5000 metres,
depending on the steepness, exposure and soil
characteristics of the slope.
Páramo is characterized by low vegetation of
10–50 cm tall dwarf shrubs, often growing as
hemispherical cushions; tussock grasses and
sedges; and herbs arising just a few centimetres
from ground level (Figure 6). All the plants are
very well adapted to night frosts of –5 to –10
degrees, very cold moraine soils, soil movement
due to the development of needle ice crystals at
night, and dry winds and extreme solar radiation
during daytime, when air temperature rises up to
+10–15 degrees or more. Rainfall is low, and
often comes down as snow, which melts within
a day or two. The soil’s coldness hampers water
uptake of roots, even in areas where the soil is
wet or there is running water nearby. However,
evaporation from leaves is high, and plants have
many mechanisms and structures to avoid dryup: dense hairiness, compact growth, very small
leaves, and thick cuticle.
The most common and striking plants are
Everlastings (genus Helichrysum with many
species), cushion-shaped, with cream or pink
coloured flowers. Adenocarpus mannii has
silvery leaves and yellow flowers, typical of the
Pea family (Fabaceae). Euryops brownei is an
erect dwarf shrub with green needle-like leaves
and bright yellow flowers like in Dandelion.
Lady’s mantle (Alchemilla) species are creeping
dwarf shrubs with woody stems, unlike the
common herbaceous ones in Northern Europe.
Festuca pilgeri is the commonest grass, and
Carex monostachya the dominant sedge; they
both grow in tall tussocks.
Further up from páramo the term Nival zone
(Cold desert belt) is sometimes used: there is no
continuous vegetation anymore, but soil is
mostly bare moraine, gravel and stones. Here
and there, even close to the glaciers, small
groups of plants can be found in places
protected by larger stones, which warm up in
daytime sunshine, and store some warmth for
the cold nights.
Giant rosette plants
In the ericaceous zone, and even more in
páramo, the giant rosette plants rise above all
the others (Figure 6). Although looking like
small trees, they are not trees in a biological
sense, but a special life form of tropical–
subtropical high mountains. They are
adaptations to an environment where no seasons
(winter) exist, soil is cold, days are warm, and
night frosts of –5 to –10 degrees are frequent,
but last only a few hours at a time.
Figure 5. Erica and Stoebe kilimandscharica forming
an endless heathland on the slopes of Mt. Kenya (P.
Pellikka).
Giant rosette plants, or megaphytes, are found in
all continents that have high tropical mountains.
In Africa such plants belong to two genera,
Senecio (groundsels, Asteraceae family) and
Lobelia (Lobeliaceae). Their taxonomy is
difficult because populations on each mountain
differ from the others; some authors
acknowledge many species while others
consider just a few, variable species to exist.
A striking feature of the megaphytes are their
massive leaf rosettes, situated terminally on
pole-like (Lobelia) or branched (Senecio) stems.
An unfolded rosette is 1–2 metres across,
containing 80–100 leaves, which have a thick
woolly underside. When temperature falls after
sunset, the leaves turn tightly inside, making a
ball around the apical bud, and protecting it
from freezing. Dead leaves often stay attached
for decades, so making an insulating cover over
younger parts of the trunk, like in Senecio
keniodendron. The thick trunk is not woody
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, 14-20. Helsinki 2004, ISBN 952-10-2077-6, 148 pp.
throughout, but its large pith contains
parenchymatous, water-storing tissue, like in
succulents. This water reservoir is needed in
early morning, when sunshine warms up the
leaves and evaporation starts, but roots are in
the still-frozen soil.
yellow according to the species. They are
pollinated by flies and other insects.
Careless smoking and frequent grass fires are
very harmful to the slow-growing Senecio
individuals. Charred and half-dead plants are
seen along the paths, and the Senecio stands no
more have the splendour that can be seen from
old photographs. Also other high-mountain
vegetation (e.g. Erica) would benefit from a
more strict control of handling fire along tourist
trails.
Origins of the high-altitude vegetation
Figure 6. Senecio brassica growing on a swamp and
Senecio keniodenrdon species behind in the páramo
zone (P. Pellikka).
Lobelia telekii has a fairly short stem, but over a
metre-tall, and candle-like inflorescence, in
which flowers are protected behind dense, hairy,
fur-like leaves. Lobelia plants die after
flowering, and on the slopes all the time both
growing and flowering individuals can be seen.
They are pollinated by sunbirds. Senecio species
are slow-growing, long-living (up to 200 years),
and the trunk divides into two equal branches
after each flowering. They seldom burst into
flower, usually once in 10–20 years, but
simultaneously over the whole mountain. Their
inflorescences are large, richly branched, and
contain hundreds of small flowers, white or
A striking feature for a European on the high
African mountains is the abundance of familiar
plant genera in the ericaceous zone and páramo,
while they are almost totally unfamiliar further
down in the forest. This dichotomy has caused
much speculation.
Some plant geographers have proposed a wellfounded theory that African mountains were
almost void of vegetation above the timberline,
until land contact was established between the
European and African continental plates in the
Middle Miocene about 18 my ago, and again 13
my ago. Then a mass migration of dozens of
cool-climate-tolerant plant genera started,
resulting in a colonisation of the African highaltitude areas. This process took place fairly
recently in an evolutionary sense, and the
temperate Eurasian plant genera are still easily
recognizable. Almost all the species, however,
are already locally developed African endemics.
Further reading
Coe, M.J. (1967). The ecology of the alpine zone of Mount Kenya. 136 p. Junk, The Hague.
Friis, I. (1992). Forests and forest trees of northeast tropical Africa. Kew Bull. Add. Ser. 15, 1–396.
Hedberg, O. (1964). Features of Afroalpine plant ecology. Acta Phytogeographica Suecica 49, 1–
144.
Lind, E.M. & M.E.S. Morrison (1974). East African vegetation. 257 p. Longman, London.
Niemelä, T. (1988). Itä-Afrikan vuoristojen metsät ja sademetsät. In: Erkkilä, A. & T. Kuuluvainen
(eds.) Tropiikin metsät. Silva Carelica 12, 57-72.
Rundel, P.W., A.P. Smith & F.C. Meinzer (eds.) (1994). Tropical alpine environments. Plant form
and function. 376 p. Cambridge University Press, Cambridge.
Vuilleumier, F. & M. Monasterio (eds.) (1986). High altitude tropical biogeography. 649 p. Oxford
University Press, New York & Oxford.
White, F. (1983). The vegetation of Africa. 356 p. + 4 maps. UNESCO, Paris.