What is a biome?
A large naturally occurring community of flora and fauna occupying a major habitat, e.g. forest or tundra. Biomes are very large areas on the earth’s surface, with animals and plants adapting to their environment. Biomes are often defined by abiotic factors such as climate, relief, geology, soils and vegetation. A biome is not an ecosystem.
Examples of biomes
Savannah or tropical grasslands
Temperate deciduous forests
What is the biosphere?
The biosphere is the layer of the planet earth where life exists. This layer ranges from heights of up to ten kilometres above sea level, used by some birds in flight, the depths of the ocean such as the Puerto Rico trench, at more than 8 kilometres deep.
Tropical rainforest lies mostly in a band either side of the equator. here, the sun’s rays are concentrated, heating moist air and causing it to rise. Heavy rainfall is the result- perfect conditions for evergreen rainforest.
Deciduous forest grows in higher latitudes. It is found in the UK and other places along the coast of continents where rainfall is high. The suns rays are less strong at this latitude, and cooler winter temperatures encourage trees to shed leaves at the end of autumn (this is what deciduous means).
Deserts are found close to the Tropic of Cancer in the northern hemisphere and close to the Trophic of Capricorn in the southern hemisphere and close to the Tropic of Capricorn in the southern hemisphere. The air that rises over the equator travels polewards after losing its moisture sinks back down at the Tropics (due to complex air patterns caused by the Earth’s rotation). The suns rays are still highly concentrated at this latitude and because the air is dry it brings desert conditions to places like the Sahara.
Coniferous forest dominates by 60 degrees north. Temperatures are so cold that trees have evolved with needle leaves that reduce moisture and heat loss.
Tundra (cold desert) is found at the arctic circle. The suns rays have little strength here and temperatures are below freezing for most of the year. Only tough short grasses can survive.
The world map of biomes does not show the variations occurring at a local level. For example, the UK is shown as entirely covered with deciduous forest- which clearly is not true. Physical factors, especially drainage, affect local conditions. In parts of Scotland, where soil conditions are especially wet, there are flat bogs rather than forests. But it is human factors- deliberate clearance of the original forests, that have caused the most change, wiping out most of the natural biome.