GE2201 : Terrestrial Environments

Monday, March 13, 2006

Tropical grasslands (savanna)

Also known as savannas, tropical grasslands are found near to the equator within the tropics of Cancer and Capricorn in South Africa, Venezuela, South America and parts of India and Australia. They form where there is not enough rain for a forest to develop and yet too much rain for desertification. Also, there are very strong winds there blow across the flat lands and these winds discourage the growth of tall trees.
Temperatures are relatively high all year round, but may vary from location to location. There are dry periods which are followed by thunderstorms bringing rain and which fill up the parched streams.
In winter, a blanket of dry sinking air smothers them, causing them to be rather dry and hot, sometimes up to 18C. After this dry spell r comes. It is considered the rainy season as warm moist air arrived from the equator. However, it is still very hot. Temperatures may exceed 25C. Precipitation varies from place to place; for example African savannas may receive three times the 18inches of rain Australian savannas get. Average annual rainfall ranges from 85 to 150cm.
There is also a surprising amount of life bursting from here. Termites and other insects living in the savannas may number up to the billions. There are also animals, mainly classified into two groups: herbivores and carnivores. The prey usually travel in herds for protection against the predators, which may sometimes follow them when they travel north to seek water during the dry seasons. The animals lose heat through large areas of exposed skin, like the elephant and its ears. Some of them prefer to avoid it entirely by burrowing underground.
There are more trees in tropical grasslands than temperate grasslands; however the concentration is still relatively low and scattered. There are also many tall grasses (some reach 5m) which are hardy and adaptable to dry conditions. These grasses have very deep root systems (compared with the tropical monsoons where prop roots are utilized) which may tap deep into the ground right to the water table. This is to enable them to survive through dry periods. The trees also have thick bark to protect against the frequent fires set by lightning, especially during the dry season. There are also numerous shrubs there, which have thorns as a defense mechanism against animals. Many of the plants grow from bottom up and have storage organs like growth buds and bulbs to make it through the dry season and ensure that not the whole plant perishes in the event of a fire. Because there are so many animals grazing on these grasses, the grasses have adapted such that grazing actually stimulate grass production instead of deterring it.
The soil is low in nutrients and permeability. Hence there are often puddles forming on the surface due to the impermeable subsoil. Since trees only survive where there is better drainage, this explains the scarcity of trees. However the grasses living in areas which get regularly flooded, like in the Llanos in South America, have adapted to be able to survive in semi-wet environments.

2:42 AM

.tts all folks.