WORLD VEGETATION
PHYSICAL GEOGRAPHY

WORLD VEGETATION

Vegetation is defined as an association or group of plants growing together in a particular habitat or environment.

 

FACTORS AFFECTING VEGETATION

Factors affecting vegetation can be grouped into four major categories. These are:

  1. CLIMATIC FACTORS
  • High temperature with low rainfall leads to sparse vegetation.
  • The higher the rainfall, the denser the vegetation.
  • High temperature and high rainfall lead to luxuriant vegetation.
  • Where temperature is low, no plant grows.
  • Sunshine provides energy for photosynthesis needed for luxuriant growth.

 

  1. GEOMORPHIC OR TOPOGRAPHIC FACTORS
  • The steeper the slope, the lesser the vegetation.
  • Rainfall on steep slopes leads to run-off, leading to low vegetation.
  • Eroded top soil in sloppy area does not support vegetation growth.
  • Given the same climate and soil, flat lands have denser vegetation.
  • In higher latitudes, aspect plays an important role on available energy and vegetation distribution.

 

  1. EDAPHIC OR SOIL FACTORS
  • The type of soil in an area affects the rate of percolation of water.
  • Sandy soils are loose and porous, leading to sparse vegetation.
  • Clayey soils do not allow percolation but support little vegetation more than sandy soil.
  • Loamy soil supports luxuriant vegetation growth.
  • The type of soil determines what plant would grow there.

 

  1. BIOTIC OR HUMAN FACTORS
  • The activities of man either support or reduce vegetation.
  • Bush burning reduces vegetation.
  • Cultivation and animal grazing reduce vegetation.
  • Deforestation also reduces vegetation.
  • Excavation and mining reduce vegetation.
  • Afforestation and irrigation support vegetation.

 

CLASSIFICATION OF WORLD VEGETATION

World vegetation is grouped into two major classes. These are:

  1. Forest: The forest is characterized by the presence of tall trees with little grasses. The forest vegetation is further sub-divided into Tropical rain forest and temperate forests.
  2. Savanna: The savanna is characterized by presence of abundant grasses with short scattered trees. It is further sub-divided into Tropical grassland and temperate grassland.

 

FOREST (Tropical Rain forest and Cool Temperate Forest)

  1. TROPICAL RAIN FOREST

Location: The tropical rain forest is found or located around the equator (i.e. within 5 degrees north and south of the equator). The forest is found in:

  • Amazon Basin of South America.
  • Zaire Basin of Central Africa.
  • The coast of West Africa.
  • Interior Malaysia.

 

CLIMATIC CONDITIONS AFFECTING THE VEGETATION

  • Favorable temperature of 26 degrees Celsius with an annual range of 2 degrees Celsius – 3 degrees Celsius.
  • It has rainfall throughout the year with two peaks (double maxima).
  • It has an annual rainfall of over 2000mm.
  • It experiences abundant sunshine and has fertile soils.

 

VEGETATION CHARACTERISTICS

  • The forest is evergreen and could be up to 60m in height with broad leaves.
  • There are various inter locking branches having layers of trees – lower, middle and upper storeys or canopies.
  • Trees are of great varieties i.e. trees are heterogeneous, big and robust.
  • The trees are not in pure stand i.e. scattered.
  • Presence of abundant hardwoods.
  • Presence of creepers, climbers, epiphytes and parasitic plants.
  • The forest has little undergrowth and sun can hardly get to the bottom or ground.

 

EFFECTS OF CLIMATE ON EQUATORIAL RAIN FOREST

  • Heavy rainfall supports numerous plants growth.
  • High temperature supports the growth of trees – the main (sea-level) temperature of about 27 degrees Celsius with a range of 1 degree – 3 degrees Celsius enhances the growth of various species of plants.
  • It has an annual rainfall of above 2000mm which supports the growth of luxuriant trees.
  • There is rainfall throughout the year and this makes the forest evergreen; hence, it is called evergreen forest.

 

PLANT COMMUNITIES

The rainforest provides tropical hardwood which includes Iroko, Obeche, Mahogany, Ebony, African Walnut, Opepe, Limba, etc. These woods provide timber for building and other construction works.

 

ECONOMIC IMPORTANCE

  • Provision of hardwood which is the source of timber used for building, furniture and other constructions activities.
  • Lumbering is one of the major occupations of the people due to presence of numerous timbers.
  • Cultivation of food and cash crops like yam, cassava, cocoa, oil palm, rubber etc.
  • Hunting of wild animals.
  • Rain forests also serve as tourist centre.
  • Provision of foreign exchange through export of timber and other products.

 

  1. COOL TEMPERATE FOREST

The cool temperate forest is also sub-divided into two as:

  • Mediterranean woodland.
  • Temperate coniferous forest.

 

  • Mediterranean woodland

Location: This vegetation is confined to western portion of continental land masses between 30 degrees and 45 degrees north and south of the equator. The forest is found in North West of Africa (Libya, Tunisia, and Morocco), South West of South Africa, Central Chile, Central California, South West Australia, France and Spain.

 

CLIMATE CONDITION AFFECTING THE VEGETATION

  • Presence of a dry warm summer with temperature between 12 degrees Celsius – 27 degrees Celsius.
  • Bright, sunny weather with hot, dry summer and wet-mild winter.
  • Abundance of rainfall in winter with mean annual rainfall of 600-800mm.
  • Abundance of sunshine with fertile soils.

 

VEGETATION CHARACTERISTICS

  • The trees are evergreen.
  • Plants are adapted to long period of drought prevalent in the region by having:
  • Tough, small, leathery, hairy leaves to guard against excessive transpiration.
  • Some plants like oak, have tough, thick bark for reducing excessive transpiration.
  • Some have long roots for drawing moisture from deep down the soil.
  • The trees have slow growth throughout the year but quicker growth during the winter rains.

 

PLANT COMMUNITIES

  • The dominant plant species are the evergreen wood plants such as oak, wild olive, cypress and redwood.
  • Presence of evergreen coniferous tree (soft wood) such as pines, firs and cedars.
  • Presence of Mediterranean bushes and shrubs such acacia, laurel, rosemary and marquis.

 

ECONOMIC IMPORTANCE

  • Orchard farming where wide varieties of citrus fruits like grape, lemon, orange, etc. are grown. They are used in wine making.
  • Viticulture which is the cultivation of grape fruits is common.
  • Production of oak cork used in corking bottle wine.
  • Trees also provide wood for construction purposes.

 

  • Temperate Coniferous Forest

Location: This forest is found only in the northern hemisphere especially in North America, former U.S.S.R., Europe and some Scandinavian countries like Norway, Sweden and Finland.

 

CLIMATIC FACTORS AFFECTING DISTRIBUTION

  • Presence of cool brief summer and a long cold winter with light rainfall.
  • Temperature range of 10 degrees Celsius – 20 degrees Celsius.
  • Winter is marked by frost and heavy snowfall.
  • Rainfall is light and convectional, which is about 500mm.

 

VEGETATION CHARACTERISTICS

  • The trees are of moderate density.
  • Almost all the conifers are evergreen.
  • The trees are conical in shape.
  • Trees are in pure stand and homogeneous.
  • Leaves are small, thick leathery and needle-shaped.
  • There is little or no undergrowth.

 

PLANT COMMUNITIES

The coniferous forest provides temperate soft wood. The major soft wood includes pine, fir, spruce and larch.

 

ECONOMIC IMPORTANCE

  • The forest provides the world’s chief source of softwood timber, used for building construction, paper, pulp and matches making.
  • The major occupation of the people is lumbering.
  • The people are also involved in hunting and trapping of some animals.

 

SAVANNA (Tropical and temperate Grassland)

  • TROPICAL GRASSLAND

Location: The tropical grasslands are located between 5 degrees and 20 degrees north and south of the equator. Areas where this grassland are found include Central America, North West part of South America, interior of Brazil, West Africa, part of East Africa, South East Asia and Northern Australia.

 

CLIMATIC FACTORS AFFECTING DISTRIBUTION

  • Presence of extremes of temperature which ranges from 21 degrees – 30 degrees Celsius.
  • Annual temperature range of 11 degrees Celsius.
  • High monthly temperature of 27 degrees Celsius.
  • Annual rainfall of about 600 – 1500mm.
  • Seasonal convectional rainfall with single maximum.
  • Summer rainfall and winter dryness.
  • Humidity is high during the rainy seasons i.e. more than 60% during the rainy season and above 40% in dry season.

 

VEGETATION CHARACTERISTICS

  • The dominant vegetation cover is grass; hence, the name given to grassland is savanna or parkland.
  • Presence of tall grasses that is fibrous when old.
  • Presence of short scattered trees.
  • The trees are deciduous i.e. they shed their leaves during dry season to reduce transpiration.
  • Grasses are succulent.
  • Trees have large trunks to store water for the dry season.

 

PLANT COMMUNITIES

  • The major plants are grasses called savanna (in Africa and Australia), campos (in Brazil) and lanos (in Orinoco in South America).
  • Popular trees include acacia, baobab and Shea-butter.

 

ECONOMIC IMPORTANCE

  • Livestock farming, due to presence of abundant grasses and low tsetse fly infestation.
  • Arable crop production in rice, maize, millet, sorghum, etc.
  • People are involved in hunting of wild animals.
  • Savanna provides for excellent centres of tourism.
  • Nomadic herding is also carried out by the local people.
  • The savanna is also used for game reserves or wildlife.

 

  • TEMPERATE GRASSLAND

Location: Temperate grassland is found in the interior continents in Asia, North America, South America (Argentina), South Africa and Australia.

 

CLIMATIC FACTORS AFFECTING DISTRIBUTION

  • The vegetation is associated with the temperate continental climate, also called the steppe.
  • Hot summer with temperature of over 20 degrees Celsius.
  • Cold winter with temperature below 0 degrees Celsius.
  • Average rainfall is about 508mm.
  • Rainfall is convectional and light.

 

VEGETATION CHARACTERISTICS

  • The dominant vegetation cover is savanna; hence, the name given to this grassland is steppe.
  • Grasses tend to have uniform height and are a bit short.
  • Grasses are succulent.

 

PLANT COMMUNITIES

  • The dominant vegetation cover is savanna.
  • The grasses have different names in different areas where they are found. These include:
  • The Steppe of Central Europe and Russia.
  • The Prairies of North America.
  • The Pampas of Argentina.
  • The Veld of South Africa.
  • The Downs of Australia.

 

ECONOMIC IMPORTANCE

  • Mechanized agriculture is practiced where crops are grown with the aid of irrigation.
  • Pastoral farming is also practiced due to abundance of grasses.
  • The grassland is used as tourist centres.
  • Nomadic herding is also carried out by the local people.
  • The savanna is also used for game reserves for wildlife (wild animals).
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