Natural Cycles and Diverse Ecosystems

Natural Cycles

In nature, chemical elements vital to life, such as oxygen, carbon, and nitrogen, are neither made nor destroyed. They are recycled, moving round and round in the natural world in the form of minerals and nutrients. On land, they move from the soil into the plants, then into animals that eat plants, and then sometimes into other animals that eat plant-eating animals. Minerals and nutrients return to the soil either through an animal’s droppings, or whenever any plant or animal dies and rots away. Microorganisms in the soil, such as bacteria, play an important part in releasing the nutrients and minerals from the decaying matter.

Polar Lands

The North Pole is surrounded by the permanently icy Arctic Ocean. At the opposite end of the Earth, the South Pole is on the continent of Antarctica. Because the poles never come as close to the Sun as the rest of the Earth, they do not have as much warmth. This means that ice and snow cover the poles all year round. To survive in the cold, many polar animals have thick fur or layers of fat in their bodies. The only humans living on harsh Antarctica are scientists studying the environment. In contrast, different groups of people, such as Inuit of Greenland and North and Canada, have lived in the Antarctic region for thousands of years. They hunt polar animals for food and clothing.

Tundra

Balance board in the Arctic Ocean are bleak and treeless, with a permanent layer of ice lying beneath the soil. This is the tundra. During the short summer, small plants and mosses grow. Herds of reindeer or caribou come from the forest further to feed them. Musk oxen stay in the tundra all year round. If attacked by wolves, they form a circle around their young.

Woodlands

Many parts of the world with a temperate climate are covered by woodlands - or would be if they had not been cleared for farmland or cities. Coniferous trees can survive in lower temperatures than deciduous trees, so coniferous woodlands are often found undistributed in northerly or mountainous regions where few people live. The trees and plants that grow in woodlands provide food and shelter for many different kinds of animals. Many of these animals are nocturnal: they come out only at night to feed on woodland plants, or to hunt other animals.

Taiga

The vast coniferous forest of northern Russia is called the taiga. During the coldest months, some animals, such as the brown bear, hibernate, while others try to find whatever food they can. Elk and reindeer scrape away the snow in their search for mosses. The crossbill uses its strange beak to extract seeds from pinecones. Predators, such as the lynx and goshawk, hunt small mammals as they search for nuts and berries.

Grasslands

Grassland is the name given to large areas of wild grass, with small plants and sometimes scattered trees. Grasslands are found in areas where there is enough rainfall to stop the land from becoming a desert, but not enough to support woodlands or forests. During the wet season in Africa, grasslands are green and rich with fresh new grass and plants. These are food for the many kinds of plant-eating animals that live there. The plant-eaters are themselves prey for meat-eaters, such as lions, cheetahs, or hyenas. In such an open landscape, there is nowhere to hide from predators, so the only means to escape for plant-eaters is to run. Many live in herds, with one member away on the lookout for approaching danger.

Deserts

A desert is an area of land which has little or no rainfall. Many deserts are hot places, bare and rocky or sometimes covered with sand. There are also cold deserts, such as the Gobi in Asia, where winters are bitterly cold. In hot deserts, temperatures can soar to over 50°C during the day. There are no trees to give shade and few places to find water. Even so, some kinds of plants and animals are still able to survive. Desert plants can take in water that condenses from dew or fog. The head-stander beetle from Africa stands on its head on foggy mornings to drink the condensation which trickles down its body.

Rainforest

Half of all the plants and animal species in the world live in tropical rainforests. Heavy rainfall and high temperatures are ideal for many kinds of plants and animals to thrive. Tall trees reach up to form a thick roof of branches called the canopy. Many animals live there, feeding on fruits and flowers. Beneath the canopy is a layer of lower trees. The forest floor is dark as little light can reach through the trees. Rivers and streams, also teeming with life, run through the rainforest. They serve as forest “highways” for the native peoples of the forest. In the rainy season in South America, the rivers flood huge areas of the forest. Fish swim in between the tree trunks.