Climates and Biomes

Climates

The Köppen climate classification system is one of the most widely-used methods of dividing the world according to climate. The system features five basic climate types. Four of these types are based on temperature, while the fifth is based on precipitation.

Summary of the Köppen Climate Classification System
climate criterion
tropical warm year-round
temperate warm summers, cool winters
continental warm summers, cold winters
polar cold year-round
arid low precipitation

Arid climate can be further divided into hot arid climate (which stays hot year-round) and cold arid climate (which features hot summers and cold winters).

World Climate Map

Biomes

Whereas climates divide the world according to annual temperature and precipitation, biomes divide the world according to prevalent forms of life. More specifically, biomes are typically classified by prevalent vegetation. Six basic types of terrestrial biome are identified here.

Summary of Basic Biome Types
biome prevailing vegetation
desert none or scattered
grassland grass
shrubland grass and shrubs
savanna trees (open canopy) and smaller vegetation
forest trees (closed canopy) and smaller vegetation
tundra grass and possibly shrubs

The forest biome is a tree-covered region with a closed canopy. Canopy denotes the above-ground vegetation of a plant community; a "closed canopy" is present when this vegetation is thick enough to prevent virtually all sunlight from reaching the ground. Thus, a region covered in trees is technically not a forest unless the branches and leaves of those trees form a continuous, dense layer that blocks out the sun.

The more precipitation an area receives, the larger and denser its vegetation; the forest biome is therefore found in the wettest regions of the world. The driest regions, on the other hand, feature the desert biome. Vegetation in a desert is either non-existent or extremely sparse, such that most of the ground is bare. (The extreme northern and southern regions of the world are referred to as polar desert; precipitation is irrelevant in these areas, since vegetation is precluded by insufficient warmth and sunlight.)

Between forest and desert lie a number of intermediate biomes. The most common is grassland (aka steppe or prairie), which is covered in grass but lacks woody plants (i.e. shrubs or trees). The term grass denotes short, narrow-leaved plants; tree denotes a tall woody plant with a single main stem; and shrub (or bush) denotes a short woody plant with multiple stems. Shrubs are generally under ten feet in height.1

The grassland biome receives somewhat greater precipitation than desert; if precipitation is increased further, one obtains shrubland (aka scrub or scrubland), which is essentially grassland with the addition of shrubs. If rainfall is increased once again, trees will appear. A biome with trees that don't form a closed canopy is called savanna; most of the world's savanna is found in Africa.

Finally, the tundra biome is found in regions too cold for tree growth, yet warm enough for smaller vegetation. Tundra lies in the sub-Arctic and sub-Antarctic regions, as well as lands of extreme elevation. Plants are limited to grass and (possibly) shrubs, as well as "surface vegetation" (e.g. mosses, lichens).

World Biome Map
1 - "Shrub", Encyclopedia Britannica. Accessed May 2010.