Forests and grasslands

Forests. The book calls a forest nature's giant green umbrella: warm, wet, and full of life from the treetops to the damp floor.

Tropical rainforests grow mainly in the hot belt around the Equator, from 23.5° N (the Tropic of Cancer) down to 23.5° S (the Tropic of Capricorn). It is hot and wet there all year, so forests grow thick. The biggest are in the Amazon Basin (South America), the Congo Basin (Africa) and parts of South-East Asia such as Indonesia and Malaysia. Smaller ones are in Central America, and in India in the Andaman and Nicobar Islands and the North-Eastern states.

Rainforests hold the richest variety of life on Earth. They keep the special inherited material (genes) of countless plants and animals. Think of the word bank: a bank keeps money, a blood bank keeps blood, and a rainforest keeps genes. That is why it is called a gene bank, useful for conservation and science.

A rainforest has floors, like a building (Fig. 2.4):

• Emergent layer: the very tallest trees poke out above the rest and get full sunlight;
• Upper canopy: the thick roof of treetops; still a lot of light;
• Understory (lower canopy): shaded; much less light;
• Forest floor: dark and damp; only a little light gets through.

In Fig. 2.4, the yellow shapes shrink as you go down. They show this: the lower the layer, the less sunlight reaches it.

Forests also help keep the oxygen in the air and balance the climate: trees take in carbon dioxide and give out oxygen. That is why forests are called the lungs of the Earth.

Grasslands are big open spaces covered mostly with grass and only a few trees. They form where rain is moderate: enough for grass, not enough for a thick forest.

• Temperate grasslands, like the prairies of North America and the steppes of Asia, have rich, fertile soil, so people farm much of them.
• Tropical grasslands, called savannas (in Africa, for example), have a few trees dotted about and big animals: lions, elephants, giraffes.

Grasslands feed grazing animals and support farming and raising livestock.