Flora of Kenya
The vegetation types in Kenya vary between extremes. While the vast plains of the Nyika plateau, but also large parts of north-western Kenya and the Mara river basin have extensive dry forests and savannah landscapes, parts of northern Kenya show true deserts whereas the wetter regions of the country boast forests of differing types, depending on the altitude of the area they grow in.
The tropical coastal belt with its warm and humid climate was covered to large extends by coastal rain forests. However, with the colonization by the Mijikenda people, the original climax vegetation shrank to small remnants. The largest remaining pieces of these coastal rainforests are the Arabuko Sokoke forest and the Boni & Dodori forests which have produced three distinct forest types depending on the rainfall patterns and prevailing soils. The Brachystegia woodland has rather poor soils which produces a light forest with interspersed grasslands. Brachystegia spiciformis, the eponymous species, provides an excellent hardwood. Today it is quite rare though, because of past overuse. The trees in the Brachystegia woodland carry long beards of lichen and epiphytes growing on their branches.
In the wetter areas of Arabuko Sokoke, a dense mixed forest prevails with valuable hardwood trees, such as Afzelia quanzensis and Manilkara sansibarensis. At least 67 native tree species exist in this type of forest. A particularly striking, ancient plant species is the palm-like cycad, which has remained virtually unchanged for millions of years.
In Cynometra forests growing on red laterite soils, the Brachylaena builensis tree can be found, which produces a timber preferred by the Mijikenda people for wood carving.
Small pockets of the original forest vegetation have survived in the sacred kaya grooves of the Mijikenda people, offering a large variety of rare reptiles, butterflies, birds and mammals a habitat.
The mixed forest covering much of the Shimba hills deserves to be mentioned separately for its large number of orchids growing on ground and trees. Between the dense rainforest patches of the Shimba hills, small areas of grassland savannahs are to be found.
In river estuaries and along vast stretches of the Kenyan coast, dense mangrove forests prevail which play an essential role preventing beach erosion. Moreover, they are the ‘nursery’ of many fish, crab and crayfish species. Over centuries, the red mangrove wood was a popular timber exported even to Arabia because of its termite resistance. Mangrove forests are composed of various tree species. Their growing area is determined by the salinity of the water and the time they are flooded by sea water at high tide. The most salt-tolerant species grow closer to the sea, brackish loving species further inland. Most mangrove species have eye-catching aerial roots for breathing and powerful supportive roots the trees cling to the oxygen-poor, muddy grounds with. Behind the mangrove zone follows a coastal evergreen bush 3-4m high.
Other forest types
Along streams and seasonal rivers in Kenya commonly referred to as laggas, another forest type pervades the dry savannahs of Nyika plateau and the grassy savannahs of the Mara basin up to an altitude of about 1500m: The riverine gallery forest. In the extremely arid northern part of Kenya these forests form up to 20m high thickets along the dry riverbeds, mainly composed of various acacia species, such as the large Acacia albida and the umbrella acacia. In wetter regions, this vegetation is complemented by wild fig tree, the branched doum palm and the raphia palm which boasts fronds up to 7m long! These green oases in an otherwise arid landscape offer numerous species of birds, monkeys, antelopes and the elusive leopard a proper habitat. Dense forests of the fever tree, an acacia with bright yellow bark, border many of the Kenyan lakes. The fever tree is an acacia bearing its name because former travelers realized they would often fall ill of malaria when being close to it. The tree, however, is not to be blamed. It simply prefers moist soil conditions, and these often are areas where standing water can be found which again offers an ideal breeding ground for malaria mosquitoes.
Many mountains of Kenya are veritable rain catchers which receive considerably more precipitation than the surrounding country. Especially their windward side often shows rain and cloud forests. These moist climatic conditions are very favorable for agricultural use and therefore the lower layers of the natural vegetation have often vanished. However, there are still a few areas where the characteristic vegetation zones of East African mountains can still be witnessed. In altitudes between 2000-3000m grows an alpine forest, between 2500-3300m follows the bamboo zone, which again is replaced by montane forests above 3500m. The afro-alpine heather and moorland zone follows up to 4600m, from where on only lichens and mosses can exist.
In highlands of up to 2500m of altitude, you will frequently witness large coniferous plantations which have not been part of the indigenous vegetation until introduction as a fast-growing tree species. Under the specific growing conditions of the coast, especially on poor coral soils, casuarina trees originating from Australia have proven successful and are often planted. The eucalyptus tree, which also stems from Australia, was brought into the country by the railway company which needed fast-growing trees for firing the steam locomotives.
In Kenya, even patches of true lowland rainforest can be found. They are constituted by Kakamega and Nandi South forests of western Kenya, marking the former easternmost extension of the Congo rainforest. Hence, the Kakamega rainforest is home to numerous tree and animal species, which stem from West and Central Africa and don't occur anywhere else in the country.
The desert areas of Kenya are confined to the northern part of the country, unless you count in alpine deserts on Mount Kenya and the hostile soda plains at Lake Magadi. Even in the dry north there are only relatively small areas with rainfall below 250mm per year, which is the geographic definition of a desert , namely Chalbi desert east of Lake Turkana, and the Kaisut desert, east of the Ndoto Mountains. Apart from few grasses, scattered shrubs and acacia trees that mainly grow in the dry riverbeds which collect the erratic rainfall, almost no plant growth can be found. The large barren lava fields in the Suguta valley also comply with the general notion of a desert.
In the dry season, the large dry savannahs that cover most of the Nyika plateau resemble a desert. However, this region receives 250-450 mm of rainfall, which is sufficient for some hardy species of acacia and commiphora bush to survive. After the rain, the landscape transforms within a few days into a deceptively green landscape with numerous grasses and flowers, before the parched ground is bare again. A characteristic plant of these areas is the whistling thorn. This acacia species develops strange hollow, blackish bulbous gourds on the branches, which are caused by a species of ant living in symbiosis with the shrub. Once these bulbs break up and the wind hits its holes, a whistling sound emerges.
Further south, the barren semi-deserts of the Nyika turn into bush savannah, which forms an impenetrable thicket reaching up to the coastal hinterland. At the end of the 19th Century, this vegetation still posed a serious obstacle for all who wanted to penetrate inland. Some maps mark this area also as Taru desert. During dry season, the bushes which can reach a height of 3-6m cast their dried up leaves. Since bush fires are a natural phenomenon in this vegetation zone, the plants have developed mechanism to resist fire. In addition to the various types of acacia and commiphora trees, boswellia plants that are related to the frankincense tree grow here, as well as the cactus-like candelabra euphorbia, a plant from the spurge family which reaches up to 6m in height and resembles a candleholder. Especially conspicuous are the massive baobab trees, which store considerable amounts of water in their stems which helps them to persist prolonged periods of drought.
The grassland savannah probably constitutes the vegetation that every tourist would call ‘typical’ African. Especially the Serengeti-Masai Mara ecosystem offers exceptionally good amounts of fodder which nourishes large herds of herbivores. This is, where you also find the most typical tree of East Africa, the umbrella acacia with its distinctive compressed crown, that often hosts whole colonies of weaver birds. The grassland savannahs are dominated by short grass growing to up to 90cm high. In very humid areas, such as the seasonally flooded plains of Ruma National Park, grass grows to up to 2m! When moving through this ‘forest’ of grass, you will feel like a dwarf.
Sweet water lakes and calm rivers often show papyrus thickets growing up to 4m in height. Especially at Lake Victoria and Saiwa Swamp National Park, fields of papyrus provide hideouts for the shy Sitatunga antelope. The Ilchamus people of Lake Baringo, commonly known as Njemps, build small rafts for fishing from the paperweight stems. The water hyacinth, that forms floating colonies on ponds and lakes, is an aquatic plant originating from South America. It is seen more frequently than one would like - despite its pretty purple flowers - , for it causes severe economic and ecological problems in the whole region.
The crop plants of Kenya show an amazing variety, depending on the respective regions, their climate and soil conditions. The coast is mainly characterized by coconut groves, as the palm tree owns an outstanding importance for the local people. Practically all parts are used for a specific purpose. From the palm fronds, baskets and mats are woven, they are also used to build the traditional makuti roofs. The sap dripping from its fruit stems is turned into the popular palm wine, mnazi, while the young fruits contain a refreshing drink which is also widely used in Swahili cuisine. The flesh of the dried fruits are used as a raw material for the oil and soap industry, and the wood is a raw material for furniture making. There are two different coconut palm varieties: the old variety with thin, long stems that reaches a height of up to 30m. It is becoming an increasingly rare sight because all replanting is done with short hybrid varieties which are said to produce higher yields and are much easier to harvest.
Many types of fruit, such as orange, jackfruit, mango, sugar cane and banana, as well as cashew nut and various spices, such as cinnamon and clove trees, are grown by local farmers. The staple food of most Kenyans consists of maize, rice and cassava. Between Mtwapa and Kilifi and in the Voi area, there are significant sisal plantations, in the drier regions north of Malindi, cotton is also widely grown. In highland regions with sufficient rainfall, mainly European fruits and vegetables are grown. Major cash crops of these areas constitute of tea, coffee and pyrethrum.