Savannah refers to wide range of plant communities ranging from unbroken treeless grassland to woodlands in which trees and shrubs form an almost continuous cover. Savanna Vegetation is categorized into two groups:
Savanna grassland: It is covers the biggest part of Uganda mainly in the central region. It covers the districts of Luwero, Kamuli, Iganga, Muyuge, Mubende, Mityana, Hoima, Apac, Lira, Kasese, Sembabule, Masaka, Mbarara and Kiruhura.
In Tanzania, it covers Northern Tanzania, Arusha, Shinyanga, Tabora, Kigoma provinces. In Kenya, it covers the eastern province and some parts of the coast province
Dry savanna wood land: This area covers parts of Kitodo, Soroti, Kitgum, Kumi, Hoima, Moyo, Nebbi, Masindi, Nakasongola and Kabarole districts in Uganda.
In Tanzania, it mostly covers the southern and western Tanzania in Lindi, Dodoma, Ruvuma, Mbeya, Mtwara, Sindiga, Kigoma, Rukwa and Iringa.
Savanna vegetation is characterized by;
The savanna vegetation varies with the amount of rainfall from wood land with long grass, through acacia woodland which has short grass and scattered trees, to open, short grasslands with thorny bushes in the semi- desert areas.
Trees and plants have adapted themselves to the savanna climate rhythm of long winter drought and short summer rain both trees and plants are therefore, deciduous in nature, shedding their leaves in the cool dry season to prevent excessive loss of water through transpiration and lying dominant during the long drought.
They have long roots (like the acacia trees) to search for ground water or broad trunks (like bottle and baobabs trees) to store up excessive water.
Trees are mostly hard gnarled, thorny and may exude gum.
Many trees are umbrella- shaped to shield their roots from the scorching heat and to expose only a narrow edge to strong trade winds that blow all the year round.
The grass is tall and coarse, growing 2 to 4 metres (6-12 feet) high. The elephant grass may attain a height of 15 metres.
The grass which grows in compact tuffs has long roots which reach deep down in search of water.
The appearance of the savanna vegetation changes with the season. It appears green and fresh in the rainy season but turns yellowish-brown and parched with the ensuring dry season.
It has led to development of the tourism industry. Savannah grassland in particular is the home of wild animals like Lions, Uganda Kobs, Giraffes and Zebra.
Livestock farming i.e. Nomadic pastoralism and Beef cattle ranching Growing of Perennial and annual crops like Sorghum, Millet, Maize, cassava, sweet
Api- culture (Bee-keeping). Charcoal burning and gathering of firewood from savanna woodlands
SEMI – DESERT VEGETATION (DECIDUOUS BUSHLAND AND THICKET/ SCRUB VEGETATION)
It covers the rest of North Eastern Uganda in the districts of Kotido, Moroto, Abin Kaabong and Nakapiripirit. In Kenya, the semi desert vegetation is found in the Northern rift valley province, North Eastern Province, part of coast province and part of the eastern province. In Tanzania, this type of vegetation is found in Dodoma, Tanga, Manyara and Sangida.
Semi-desert vegetation is characterized by;
- Most of the scrubs have long roots and are well spaced out to gather moisture and search for ground water.
- Plants have a few or no leaves and the foliage is waxy, leathery, hairy or needle-shaped to reduce the loss of water through transpiration.
- The seeds of many species of grasses and herbs have thick, tough skins to protect them while they lie dormant.
- They germinate at once when their seeds are moistened by the next rain.
- Some of the plants are entirely leafless, with pricks or thorns.
- The predominant vegetation in semi-desert area is Xerophytic or drought-resistant scrub. This includes the bulbous cacti thorny bushes, long-rooted wiry grasses and scattered dwarf acacia.
- It has led to the development of the Tourism Industry i.e. Kidepo Valley National Park.
- Nomadic Pastoralism by Karamojong, Matheniko, Masai and Galla
- Growing of drought resistant crops like millet, Sorghum in Abim.
MOUNTAIN/ MONTANE VEGETATION
This type of vegetation is found on the slopes of Mountain Rwenzori, Mountain Elgon, Muhavura Mountain, Kilimajaro Mountain, and Kenya Highlands. The vegetation is not uniform all over the mountain due to the effect of latitude, temperature, moistures availability and slope steepness.
The vegetation zonation starts at the base of the mountain
At the base there is savanna vegetation (or often, at the lower levels, dry bush or scrubs, grading upward into Savanna grassland and then into woodland, which finally merges into true forest).
– On the lower slopes of the mountain where the rainfall totals are high, there is thick forest (rain forests –at the lower levels grading upward into temperate forests) at 1800metres above sea level.
Temperate forest is not as large as those in the equatorial forests, and with altitude they become smaller. Ferns and Epiphytes are abundant. The leading species of trees in these forests include podocarp, Cedar and Camphor. Near its upper limit, these trees dwindle to low forests that are densely populated with mosses.
Above 3000 metres, this forest usually merges into a very dense thicket of Bamboo.
Above 3,500metres, the vegetation is limited to treeless vegetation. The plants found at this level are adapted to cold and bleak conditions, and the vegetation is alpine, scrub, grassland and heath.
Other plants in this zone include giant lobelia, giant groundsel, and bromeliad (Heath and moorland. The upper limits of plant growth in East Africa are between 4400 – 4500 metres.
Above 4500 metres there is snow and bare rocks because the temperatures are too cold to permit plant growth as illustrated below
They are characterized by the following
- Have single canopy.
- Absence of undergrowth
- Thick cover of moss/cabbage leaf growth and tress ferns
- Threes change with attitude i.e. tropical rain-forest, bamboo, temperate
Growing of tropical and temperate crops like wheat, barley, pyrethrum, coffee (Robusta), banana, Oranges, on the lower and upper slopes of mountain Elgon.
Dairy farming because of the low temperature in Kenya highlands.
Lumbering (presence of Equatorial and temperature forests), this has resulted into the development of pulp and paper industry, soft board and match sticks.
Development of Tourism (flora and fauna), Bamboo shoots are source of food in Mbale, Sironko, Manafwa
This type of vegetation is found in areas that either seasonally (periodically) or permanently flooded. There are two types of swamp vegetation.
Swamp forests: There are swamp forest dominated by trees and other woody vegetation. They are mainly found in the Sango Bay area in Rakai district. Swamp vegetation dominated by tall herbaceous vegetation.
This type of vegetation occurs at the edges of Lakes like Kyoga and Victoria and along the river valleys like river Katonga, Mpologoma and Kagera in Uganda. Swamp vegetation is found in Lorian plains, Boji plain along river Bongal, along river Tana in the coastal area in Kenya.
Along rivers Malagarasi, Wembere, Pangani, Great Ruaha, Kilombero, Northern shores of Lake Rukwa and along River Mara in Tanzania
- Art and Craft Industry
- Papyrus for the production of Bio-gas
- Growing of crops – Irrigation schemes like Doho, Kibimba,
- Fishing and fish farming in Bushenyi
- Brick, tiles making from clay
- Grazing of animals
They are found along the coastal areas of both Kenya and Tanzania.
They are characterized by:
- They have medium height trees.
- They have hard wood species.
- They have short stumpy trunks
- They have evergreen broad leaves.
- They are dense with bushy stands.
- They have twisted trunks.
- They have stilt roots.
FACTORS AFFECTING THE DISTRIBUTION OF NATURAL VEGETATION IN E.AFRICA PHYSICAL FACTORS CLIMATE
The natural vegetation is a direct response to the type of climate experienced in area. It mainly influences vegetation through the aspects of rainfall and temperature.
- Areas with heavy well distributed rainfall over 1500mm with double maxima high temperatures throughout the year are covered with equatorial vegetation.
- Areas receiving moderate and seasonal ranging between 600mm – 800mm, savanna vegetation are common.
- Areas with unreliable and low rainfall less than 550mm with very hot temperature are covered with thicket, scrub and dry bushes.
It affects vegetation distribution and growth by influencing the rate at which water moves to the surface.
- Steep slopes experience rapid water movement/ flow hence little water is left for plants and as a result there is stanted vegetation.
- On the gentle slopes, the speed of water is slow and this allows deep penetration of water into the ground and as a result the gentle slopes have well developed soils and dense vegetation
- Relief also influences vegetation in as much as it determines rainfall distribution and formation. The wind ward side receives high amount of rainfall hence thick vegetation compared to the leeward side which has poor vegetation.
The mineral composition, depth, maturity, acidity and alkalinity of soil directly influence the type of soils directly influence the type of vegetation.
- Thin immature skeletal soils on steep slopes of the mountains
- Highland soils which are rich in organic matter give rise to dense vegetation on the slopes of Mountains of East Africa o The rich fertile loam soils around Lake Victoria support dense equatorial vegetation.
- The rich fertile volcanic soils support dense vegetation cover.
- The poor sandy soils have semi desert vegetation. o Sandy loam soils (dry Land soils) support savanna grassland.
Well drained areas supports different types of vegetation like equatorial vegetation o Water loving plants like papyrus, are found in poorly drained areas.
It is the height above sea level. It plays an important role in influencing vegetation zonation through its influence on temperature and rainfall.
Other physical factors include; pests and diseases, wild animals and natural fires.
- Cultivation of land destroys the original vegetation types like equatorial forests are replaced by perennial crops like coffee, tea. Abandoned areas regenerate secondary forest vegetation and Savanna grassland degenerate into scrub.
- Bush burning causes destruction or elimination of original vegetation species and promotion of fire resistant species o Overgrazing leads to loss of vegetation cover
- Swamp reclamation either for settlement or industrial developed Urbanization, settlement, road and railway construction leads to clearance of natural vegetation o Cutting trees for fuel i.e. Tea curing, fish smoking, Brick baking
- Agro-forestry: introduction of new plant species
- Reafforestation and afforestation programmes to replace original forests with quick growing trees. o Gazette some areas of natural vegetation for conservation o Planting of Peri-urban plantation to meet future wood requirements in Kampala.