Biomes

Biomes are large scale ecosystems. They are defined by factors such as climate, soils and vegetation. The world's major biomes include rainforest, desert, savanna grassland and tundra.

Ecosystems are communities of plants and animals that live in a particular environment. They range from small ecosystems such as a freshwater pond, to global ecosystems such as deserts. They contain biotic and abiotic components.

Biotic means living things like insects, plants, trees and mammals.

Abiotic means non-living things such as soils, rocks and the climate.

• Tropical forests are found near the equator in Central and South America, parts of Africa and Asia. They are hot and humid and contain a huge variety of plants and animals - around half of all the world's species. The trees are mostly hardwood. The climate is called equatorial.
• Savanna or tropical grasslands are hot and dry, dominated by grass, scrub and occasional trees. They have two distinct seasons - a dry season when much of the vegetation dies back, and a rainy season when it grows rapidly. They are found in central Africa (Kenya, Zambia, Tanzania), northern Australia and central South America (Venezuela and Brazil).
• Desert is the driest and hottest of areas. The world's largest desert is the Sahara in North Africa. Areas of scrub land that border the desert are called desert scrub.
• Temperate deciduous forests contain trees that lose their leaves and are found across Europe and USA. The weather is mild and wet. The climate is called temperate maritime.
• Coniferous forests, containing evergreen trees, are found in Scandinavia, Russia and Canada. They have a cool climate with moderate rainfall called cool temperate.
• Tundra/Polar surrounds the north and south poles. They have an extremely cold climate, with limited numbers of plants and animals able to survive there.

Climate is the average weather conditions over a longer period and over large areas.

The temperature and the amount of rainfall an area receives depend on:

• geographical position in relation to the poles and equator
• the effect of any nearby large water bodies such as seas and oceans
• the way that the landscape changes in height, which is called relief

Climate graphs show the average annual rainfall and temperature throughout the year for a particular area. They can give us a better understanding of the type of climate experienced in a biome. This is an example graph:

This graph shows temperature and rainfall of a tropical rainforest. The example graph shows that there is a distinct rainy season from December to May. The amount of rainfall varies over the year - with the highest monthly rainfall in March with over 300mm, while the lowest is in August with less than 50mm. Over the year, the temperature only varies by 2°C.

Other biomes would also have distinct climate graphs. The desert biome would receive very little rainfall across the year with average temperatures being high throughout. A deciduous forest would have a milder temperature and a consistent amount of rainfall all year round.

In order to survive in each biome, plants and animals have had to adapt to cope with the environment they live in and the challenges they might face.

Here are two examples of how animals have adapted to their habitat.

Deforestation is the clearing of large areas of trees. It is a particular threat to tropical rainforests in places such as the Amazon Basin.

Increased human activity has led to large portions of the forests across the world being lost. This is mainly as a result of:

• logging - trees like mahogany are cut down and sold for timber to make furniture. Other trees are cut down for making paper products
• farming - large areas of the rainforest are cut down to make areas for cattle ranches that produce beef
• mining - the Amazon Basin is rich in natural resources such as iron ore, copper, tin, aluminium, manganese and gold. Areas are cleared to get access to these resources

The trees and plants of the Amazon Basin absorb carbon dioxide. If there are fewer trees and plants, due to deforestation, then less carbon dioxide is removed from the atmosphere. In this way deforestation contributes to global warming and therefore climate change.

As forests are cleared, animals lose their habitats and sources of food, forcing them to move elsewhere and, in some cases, leading to extinction.

The orangutan is a prime example of a threatened species. Once widespread across south-east Asia, today orangutans are found only on the islands of Sumatra and Borneo.

A reason why they are a threatened species is because the rainforests where they live are being cut down to make way for agriculture, including the growing of trees for palm oil plantations.

Climate change affects the world's biomes.

In arid and semi-arid biomes, desertification is becoming more common. Desertification is a reduction in the productivity of the land, either temporarily or permanently. As a result, the land is less able to support plant growth than it was in the past.

Desertification can be caused by several factors, including:

• drought
• deforestation
• overgrazing
• fire
• overfarming

When land becomes less productive, it can be more difficult to farm and can lead to economic challenges.

Polar biomes are affected by rising global temperatures. In many areas, the extent and thickness of sea ice have decreased.

Changes to sea ice and habitats can make it more difficult for animals such as polar bears and walruses to find food and breeding grounds. As a result, some animal populations have migrated further south in search of land and food to sustain themselves.

In Antarctica, reductions in sea ice can affect penguin populations that depend on it for feeding and breeding.