Write a geographical account of Tropical Grasslands under the following headings: (a) Location; (b) Climatic factors affecting the distribution; (c) Vegetat...

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A Geographical Account of Tropical Grasslands (Savanna)

(a) Location

Tropical grasslands, also called the Savanna, lie between latitudes 5° and 20° North and South of the Equator, forming a broad belt on either side of the equatorial forest. The main regions are:

• Central America and the Llanos of northern (north-western) South America.
• The interior of Brazil (the Campos).
• The interior of West Africa (the Sudan belt, e.g. northern Nigeria).
• Parts of East Africa (Kenya and Tanzania).
• South-East Asia and Northern Australia.

(b) Climatic factors affecting the distribution

The distribution of the Savanna is controlled by the seasonal migration of the rain-bearing winds, which gives a hot climate with one wet season and one dry season. Its main features are:

1. High mean monthly temperatures of about 27°C throughout the year.
2. A fairly high annual temperature range of up to about 11°C.
3. Moderate annual rainfall of about 600 mm to 1500 mm.
4. Rainfall is seasonal with a single maximum, concentrated in the high-sun (summer) months.
5. Summer rainfall and pronounced winter (low-sun season) drought.
6. Relative humidity is high (above 60%) during the rains and lower (about 40%) in the dry season.

These figures are best shown on a climate graph of a typical Savanna station. The temperature curve stays high all year while the rainfall bars rise sharply to a single peak in the wet season, confirming the wet-and-dry rhythm of the region:

From the graph, total annual rainfall is about 867 mm (within the 600 to 1500 mm range), the wettest month is August (250 mm) while November to February are almost rainless. Temperature ranges from about 22°C in the coolest month to 32°C in the hottest, a range of about 10°C, and the mean is roughly 27°C. The single rainfall maximum and the constantly high temperatures are the two climatic controls that separate the Savanna from the equatorial forest to the south and the desert to the north.

(c) Vegetation characteristics

1. The dominant vegetation cover is grass.
2. Tall grasses with fibrous roots, such as elephant grass, dominate the wetter margins.
3. Short, scattered trees grow among the grasses, giving a park-like appearance.
4. The trees are largely deciduous, shedding their leaves in the dry season to reduce water loss.
5. Many trees have large trunks that store water for the long dry period.
6. Common trees include the Baobab and Acacia.
7. Most trees have rough, thick and thorny bark as protection against drought and fire.
8. Grasses are often succulent during the rains but wither and turn brown in the dry season.
9. A typical grass of the region is the elephant grass.