To what extent has altitude influenced vegetation distribution in East Africa?
The candidate is expected to: ·
- Define vegetation.
- Identify the vegetation types in East Africa and their location.
- Examine the role of Altitude.
- Examine the role of other factors.
Vegetation is plant cover on earth’s surface.
Vegetation types in East Africa include:
- Tropical rainforests found on shores of Lake Victoria like Mabira; Western Uganda like Maramagambo, Budongo, Bugoma, Itwara, Kalinzu.
- Mangrove forests found on the East African coast at the out skirts of Mombasa, Dar es salaam
- Montane forests (Temperate forests and Bamboo forest) found in highland areas like Mt. Kilimanjaro, Mt. Kenya, Mt. Elgon etc.
- Savanna woodlands like Miombo woodland in Western and Southern Tanzania and isolated areas of Northern Uganda.
- Savanna grassland in Northern Uganda, parts of western Rift Valley in Uganda, Bukoba area in Tanzania, southern Kenya.
- Dry bush, scrub and thicket like Ankole, Masaka corridor, North Eastern Uganda, Turkana land in Kenya, Central Tanzania.
- Desert vegetation e.g. Chalbi desert, Kenya.
- Heath and Moorland on upper slopes of mountains like Kilimanjaro, Kenya.
- Papyrus swamps in lowlands surrounding lake like Victoria, Kyoga and some valleys.
Altitude has influenced the vegetation in East Africa as below through influencing climate, soils and drainage.
Between 0-1000 m above sea level there are mangrove forests like on East African coastal areas particularly belt of Tanzania. They are characterized by evergreen trees, with broad leaves, short stumps and trunks, aerial roots.
Conditions:
- Hot temperatures.
- Heavy rainfall of over I000mm.
- Poorly drained soils.
In some areas at this height there are mixed forests with deciduous, some with thorny trees like acacia, tall grass like western rift valley.
Between 1000-2000 metres above sea level, is savanna vegetation with different savanna vegetation types. Savanna woodland in areas like western Tanzania and isolated areas in Northern Uganda characterized by continuous cover of trees, umbrella shaped trees, with hard barks, deciduous trees, drought resistant trees etc.
Conditions:
- Moderate rainfall 750-lOOOmm.
- Hot temperatures.
- Well drained soils.
- Fairly fertile soils.
Savanna grasslands in Northern Uganda i.e. Kitgum, Nakasongola, Mbarara, Bukoba area in Tanzania etc. characterized by tall grass, elephant grass and spear grass being common, scattered trees which are deciduous. tree like acacia and Baobab, trees and grass drought resistant etc. ‘
Conditions:
- Moderate rainfall 500-750mm.
- Hot temperatures.
- Fairly fertile and well drained soils.
Dry savanna (Dry bush, scrub and thicket). Characterized by drought resistant grass, drought resistant trees, trees are short and scattered, trees have small leaves, thorny bushes etc. these can be found North Eastern Uganda, North Western Kenya, Ankole Masaka corridor etc.
Conditions:
- Low rainfall 300-500mm.
- Hot temperatures.
- Infertile soils in most areas.
- Well drained soils.
Between 2000-2500 metres above sea level there are tropical rain forests like Budongo, Bugoma, ltwara, Maramagambo, Mabira, and on lower slopes of mountains like Kilimanjaro, Elgon etc. They are characterized by tall trees of up to 50 metres, thick canopy, evergreen trees, broad leaves, climbing plants like Lianas, trees have buttress roots etc. ·
Conditions:
- Heavy rain fall.
- Hot temperatures.
- High humidity around 80%.
- Fertile well drained soils.
Between 2500- 4000 metres above sea level there are montane forests with forests with temperate forests at 2500-3500 metres above sea level. These are characterized by trees like camphor, podocarp, Cedar with small leaves and evergreen as well as Bamboo forests at 3500 – 4000 metres above sea level. Trees are characterized by appearing in single layers, trees are evergreen with prop roots.
Conditions for growth
- Low temperatures..
- Moderate to low rain fall.
- Fairly thin well drained soils.
Between 4000 – 4500 metres above sea level there is heath and moorland characterized by grass, flowers, shrubs and plants; like the giant groundsel/lobelia etc.
Conditions for growth:
- Low rainfall
- Low humidity.
- Cool temperatures.
- Thin, infertile soils.
However there are other factors that have influenced vegetation types in £.Africa.
Climate
- Heavy rainfall of over 1000mm, hot temperatures, high humidity of around 80% lead to growth of tropical rain forests and mangrove forests.
- Moderate rainfall to low rainfall (3 00- 1OOOmm), hot temperatures lead to growth of savanna vegetation.
- Low rainfall of less than 300mm and hot/ very hot temperatures led to desert vegetation e.g. chalbi desert.
Soil
- Deep and fertile soils lead to growth of tropical rainforests.
- Poorly drained soils lead to growth of Mangrove forests and papyrus swamps.
- Fairly fertile soils have led to growth of savanna wood land and grass land.
- Thin, infertile soils support growth of heath and moorland.
- Most dry savanna areas and desert vegetation areas have infertile soils.
Relief
- Coastal lowlands and some river valleys have led to growth of Mangrove forests.
- Lowlands and gentle slopes have led to growth of tropical rain forests and savanna vegetation.
- On steep slopes of high mountains there is growth of montane forests, heath and moorland.
- In areas of poor drainage in lowlands and valleys, there is growth of Mangrove and Papyrus swamp vegetation
- Poorly drained areas of high mountains, there is growth of heath and moorland.
- Well drained plateau areas have sustained growth of savanna woodland and savanna grassland.
Human activities,
- Cultivation of crops, grazing of animals, mining and quarrying, burning, construction of settlements has led to clearance of initial vegetation and growth of secondary vegetation.
- Afforestation and re-afforestation has led to growth of artificial/ planted forests like Muko, Mafuga, Lendu.
- Government policy of conservation has led to growth of forests in national parks, Game reserves and forest
- reserves while savanna vegetation has been conserved in relatively dry areas.
