Biomes The Broad Vegetation Types Of The World

On the broadest scale, certain forms of vegetation occur again and again, scattered between different places around the planet. Depending on how finely you might choose to subdivide them, there arc between five and twenty fundamental vegetation types in the world. They include, for example, tropical rainforest and savanna in the tropics, and in the high latitudes temperate forest and steppe. Such broad-scale vegetation types are known as "biomes". and each one of them is distributed between several continents (Figure 2.1a*).

The distribution of biomes is not random—it depends mostly on climate, although underlying rock and soil type and local drainage conditions also determine the precise limits of each biomc. Humans have also influenced the vegetation through burning, forestry and agriculture, so that in some placcs one finds that a biomc has been rcduccd or shifted in area in response to human disturbance during the last few-thousand years (Figure 2.1b*).

Exactly how broadly or narrowly a biomc is defined can vary between one ecologist and another. For instance, most ecologists would define the world's tropical evergreen forests (tropical rainforests) as a biome by itself, but others would also tend to lump this and various other types of tropical forest into a single larger "tropical forest" biome. Some would even include all forests anywhere in the world— as part of a grand "forest" biomc.

Each biome is made up of thousands of individual plant species. Although tending to lit in with the general growth pattern and appearance of the biome. each of these species has its idiosyncrasies. A species also has its own distribution pattern, determined by its specific requirements for climate and soil, and also the chance legacies of history.

* See also color section.

water land ice oesert coa na. coa wot coa bl evo tree occ tree dec tree coa un warm Na tree evc tree

WARM 81

dec tree mx tree water land ice oesert coa na. coa wot coa bl evo tree occ tree dec tree coa un warm Na tree evc tree

WARM 81

dec tree mx tree trop evc trop occ evc tree tree savannah tuno« a ocao coa for warm for tundra crop crop coa crass warm crass tundra evcrn shrub oeco shrub semi coa irr desert crop coa crop warm rr crop warm crop forest non-f wetland wetland

Figure 2.1. (a) Map of major biome distributions. This is for "natural" vegetation as it would be without human disturbance, based on what we know of broad climate vegetation relationships. The categories vary somewhat between different authors and so show up differently on different maps. Source: Chase et al. (2000).

In this chapter we will explore the ways in which climate selects and shapes vegetation, both in its general form (as in a biome) and in the detailed appearance and composition of spccics within it. Then, in the next chapter (Chapter 3) we will take a look at how vegetation can move if the climate changes.

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Renewable Energy 101

Renewable Energy 101

Renewable energy is energy that is generated from sunlight, rain, tides, geothermal heat and wind. These sources are naturally and constantly replenished, which is why they are deemed as renewable. The usage of renewable energy sources is very important when considering the sustainability of the existing energy usage of the world. While there is currently an abundance of non-renewable energy sources, such as nuclear fuels, these energy sources are depleting. In addition to being a non-renewable supply, the non-renewable energy sources release emissions into the air, which has an adverse effect on the environment.

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