GCSE Revision - Ecosystems - Savanna Grasslands

 

Savanna Grassland Facts

  • The vegetation consists of grasslands with some woodland with isolated trees such as baobab and acacia

  • It is suggested the grasslands have been developed because of fires started by thunderstorms or deliberately by people to encourage new growth of grass

  • The Tropical Savanna Grasslands are found in the centre of continents between 5 and 15 degrees north and south of the equator

  • Temperatures are high throughout the year averaging around 28 degree centigrade

  • There are clear seasons of wet and dry weather

  • Rainfall is convectional with very heavy downpours

How does the vegetation adapt to the climate?

  • The vegetation must survive  the long period of drought and the fires during the dry season

  • Grass grows quickly - up to 130cm high during the short rainy season

  • Baobob trees store water in their trunks and have thick bark which protects against fire and reduces moisture loss

  • Trees have few leaves so less moisture is lost through evaporation and transpiration - leaves are small, waxy and thorny to reduce moisture loss

  • Trees lose their leaves through the dry season to conserve moisture

  • Trees have long roots so as to extract water from the deep ground

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Savanna Soils

 

  • The soil of the Savanna is called Laterite

  • The surface has a hard crust caused by the alternate wet and dry seasons

  • When the hard crust is broken up by ploughing it easily eroded

  • The soils are leached during the wet season and the iron oxides that remain give it the red colour

  • The soils contain few nutrients and tend to be acidic

  • Hard layers prevent drainage and it is not easy for roots to penetrate

Human Impacts in Savanna areas - Desertification in the Sahel

 

  • Desertification is the spread of desert like conditions into dry grassland areas.

  • A desert has less than 250 mm of precipitation per year

  • Every year 12 million hectares of land are becoming a desert

  • The area most at risk from desertification is North Africa - the Sahel Region

The Causes of Desertification

  • Climate change - Many years of drought have been experienced in some areas and average rain has been decreasing

  • Farming - Declining death rates have caused populations to increase - more food and resources are needed and fragile areas have to be farmed

  • Overgrazing - Increase in the numbers of cattle etc has removed vegetation

  • Irrigation - Pumping of water from underground to water crops has reduced the level of the water table - tree roots can no longer reach water supplies

  • Deforestation - Trees have been cut down for fuel and building materials

  • Erosion - When vegetation is removed, soil is no longer held together by roots - soil is eroded by wind in the dry season and by water in the heavy rains of the wet season

The Effects of Desertification in the Sahel

  • Lack of vegetation for grazing will be severe as it is in an LEDC

  • Crop failure will lead to famine and possibly death for people eg Ethiopia in 1984

  • Rural to Urban migration will occur as people leave the countryside

  • Refugees may cross borders in search for food

Just click on the image opposite for two very good animations on the causes - effects and methods to control desertification!

Preventing Desertification

  • Magic Stones - Stone lines are built following contours which slow surface run-off and prevents soil erosion

  • Contour Ploughing - Ploughing parallel to contours - not up and down which also limits soil erosion

  • Planting lines of trees - Reduces wind erosion and if used carefully can provide wood for fuel

  • Drought resistant plants - These may be used to stabilise sand dunes and start the successful development of vegetation

Human Impacts in Savanna areas - The issue of Wildlife, Tourism & Growing Populations

Wildlife & Growing Populations

  • In many parts of Africa many of the wild animals are now protected.

  • This means especially with elephants the increasing numbers can cause great damage to the ecosystem

  • They can also cause conflicts with the local population as they become hungry

  • The wild animals can destroy much of the crops and food intended for the growing population

Tourism

Although tourism can bring many benefits to an area it can also bring many problems:

  • Subsistence farmers living around the edges of the national parks come into conflict with the wildlife

  • Much of the income from tourism does not go to local people

  • Farmers grow crops which help to destroy wildlife habitats

  • Damage is caused by the tourist vehicles

  • Tourism creates environmental pollution to rivers and the countryside

Possible Solutions


In 1991 the Campfire scheme was set up in Zimbabwe where wild animals are being farmed so as to provide game for hunters who pay up to £4600 to kill an elephant. Local communities receive cash payments and compensation for crop losses by wild animals. Attitudes to wildlife has changed and locals are far more eager to put up with the problems of wild animals.

In Kenya they are experimenting with the contraceptive pill for elephants in the hope of cutting the numbers

In other areas culls have taken place or animals have been captured and shipped to other areas

In some African countries they are even advocating the return of the trade in Ivory so as to pay for the increasing cost of the wildlife.
 

Links - Revision DVD - Various programmes on

  • Tropical Rainforest

  • Coniferous Forests

  • Savanna Grasslands

Common Questions

  • What is the relationship between rainfall and vegetation shown on a graph

  • How has rainforest plants adapted to the climate

  • What are the main threats to the tropical rainforest

  • What have the effects of deforestation had on the soil, rivers, etc

  • How can tropical rainforests be better managed for the future

  • How have Coniferous trees adapted to the climate

  • How is the Coniferous Forest been managed

  • Why is Podsol soil acidic

  • What are the main features of savanna grasslands

  • How has Savanna vegetation adapted to the climate

  • What are the causes of desertification in savanna areas

  • What are the effects of desertification and how can the effects be minimised for the future