LW-distribution+of+ecoystems

__**The distribution of global ecosystems**__


 * The big ones**

The world can be divided up into 8 big ecosystems, or biomes. Each one has its own type of vegetation. The locations and characteristics of each biome are mainly etermined by climate. This is because climate affects the growth conditions for vegetation. It does this through:
 * Temperature - especially the seasonl pattern and he length of the gorowing season
 * Precipitation or rainfall - particularly the total amount and how it's distributed throughout the year
 * The number of sunshine hours - which determines the amount of light available for photosynthesis
 * Rates of evaporation, transpiration and humidity

The map below shows the distribution of the world's main ecosystems/biomes.



You need to be able to describe the distribution of the 3 ecosystems we will investigate:


 * Tropical rainforest - Generally found between the Tropics 23.5 degrees north and south, also across the Equator, found on the west coast of Africa, a lot on the east coast of continents such as South America, covers most of the islands in Indonesia
 * Deciduous Woodland - often found north of the Tropic of Cancer, so mainly all in the Northern Hemisphere, can be found on both the coast and inland areas of continents such as Asia and North America, The largest expanse is across Northern and Eastern Europe spreading right across Northern parts of Asia
 * Hot Deserts - often found around the Tropics – 20 – 30, degrees north and south, more extensive in Northern Hemisphere, a number are on western side of continents such as South America and Africa. The largest expanse is across northern Africa, into the Middle East and Asia

__**Explaining the global distribution of ecosystems**__


 * Temperature**

Average temperature is the main factor affecting plant growth. Temperature gradually decreases as you move away from the Equator. In the Tropics, the sun's rays are at a high angle in the sky for the whole year - and are concentrated over a smaller area than at the Poles. They provide a lot of heat and sunlight, so plants grow well here and vegetation is dense. In Polar areas, the sun's rays are less concentrated. The lack of heat and light limits vegetation growth, so plants are stunted and low growing.


 * Precipitation**

Around the world, precipitation is more likely in some places than in others. Pressure belts determine how much rain an area receives. These belts give rain all year and are found at the Equator and at mid-latitudes. Forests grow in both these areas. In high pressure belts, the air is descending and you get dry conditions - creating deserts. The North and South Poles are high-pressure areas with dry conditions. The pressure belts move and this can create seasons in different places


 * Local factors**

Other factors affecting plant growth include:
 * **altitude** - temperatures decrease by 1 degree for every 100 metres in height. So, the top of Mount Kilimanjaro in Tanzania is covered in snow, although it's near the Equator
 * **continentality** - this is the term for distance from the sea. Away from the sea, the land heats up in the summer and cools quickly in the winter. This increases the annual temperature range and reduces precipitation
 * **nutrient-rich environments** - environments rich in nutrients to encourage plant growth. Nutrients are supplied by the soil or ocena currents
 * geology (rock type), soils, relief and drainage and water

__**Key terms**__

Temperate deciduous forest: forests comprising broad-leaved trees such a oak that drop their leaves in the autumn.