BIOMES

Biomes are climatically delineated assemblages of organisms that have a characteristic appearance and that are distributed over a wide land area. Biomes are classified in several ways, but, for our purposes, we will discuss them under seven categories: (1) tropical rain forests, (2) savannas, (3) deserts, (4) temperate grasslands, (5) temperate deciduous forests, (6) taiga, and (7) tundra. They vary remarkably from one another because they have evolved in regions with very different climates. The distributions-of the principal biomes that we will discuss, along with those of some of the related communities.

If there were no mountains and no climatic effects caused by the irregular outlines of the continents and by different sea temperatures, each biome would form an even belt around the globe. In fact, their distribution is greatly affected by these factors, especially by elevation. Those biomes that normally occur at high latitudes follow an altitudinal gradient along mountains, thus the summits of the Rocky Mountains are covered with a vegetation type that resembles tundra, whereas other forest types that resemble taiga occur further down. It is for reasons such as these that the distributions of the biomes are so irregular. We will now examine some of the distinctive features of the individual biomes, using the seven enumerated before to organize our discussion.