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S.3 Geography Notes

Factors affecting the distribution of natural vegetation in 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 and experience warm-hot 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.

Relief or topography

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 stunted 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.

Soil

The mineral composition, depth, maturity, acidity and alkalinity of soil directly influence the type of soils directly influence the type of vegetation.  Soils factors influencing vegetation type according to their moisture content for example peat soils give rise to riverine forests and swampy vegetation. Soils devoid of moisture like sandy soils give rise to scanty or scrub vegetation. Highland soils which are rich in organic matter give rise to dense vegetation on the slopes of Mountains of Africa.

Drainage

Well drained areas influence vegetation leading to growth of different types of vegetation like equatorial vegetation and grassland In flat areas and valleys, the drainage is likely to be impended and characterized by swampy conditions leading to the growth of Water loving plants like papyrus and mangrove vegetation.

Altitude

It is the height above sea level. Altitudinal differences lead to vegetation zonation due to changes in soils and climatic conditions. The lower altitude areas have savannah grasslands and mid slopes support deciduous forests and bamboo. High altitude areas allow the growth of heath and moorland.

Organisms like wild animals’ influence vegetation distribution through overgrazing, the vegetation changes to secondary type for example in some parts of Queen Elizabeth national park.  Insects like locusts in Senegal and termites are common in the savannah woodland areas destroy the vegetation in those areas.

Latitude:

Latitude has influenced the natural vegetation in the following ways: In the range of 00 - 50 north and south of the equator are areas of low latitude which support the growth of tropical rain forests due to heavy rainfall and warm – hot temperatures throughout the year. In range of 060 – 150 north and south of the equator, savannah grasslands occur due to alternative dry and wet season In the range of 150 – 350 north and south of the equator, there is semi-arid or scrub vegetation dominated by poor grass and thorny trees. The Mediterranean type is found on north western tip of North Africa in the range of 300 - 350 north and south of the equator, western tip of South Africa due to wet winters and warm dry summers.

The effect of dry winds has led to the growth of scanty vegetation in some parts of Africa. Areas adjacent to the cold current like canary and Benguela lead to scanty vegetation.

Human activities

Man’s activities which include cultivation, industrialization, overgrazing, bush burning and forestry activities lead to the growth of the secondary vegetation or have reduced vegetation cover to scanty vegetation or modification of the vegetation Agro-forestry, Reafforestation and afforestation programmes to replace original forests with new plant species or quick growing trees.

Government policy to determine the location of vegetation for example through gazetting some areas of natural vegetation for conservation

Reasons for reduction in natural cover in Africa

  • Human activities like clearance land for settlement, agriculture, road construction, and industrialization.
  • Destruction of forests by wild fires or natural fires
  • Destruction of vegetation by wild animals like elephants
  • Prolonged drought resulting into desertification
  • Loss of vegetation by pests like desert and red locusts and termites and diseases
  • Occurrence of landslides and mass wasting in the mountainous areas due to heavy rainfall
  • Flooding
  • Pollution

Discussion

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