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Progressive changes in temperature, solar radiation, and precipitation from the equator toward the poles and similarly from the low-lands to the mountain peaks control the distribution of certain major vegetation types and these, in turn, are accompanied by characteristic sets of plants and Associated animal species.
As a result, we may recognize a series of life zones or terrestrial habitats extending across the land from the tropics to the Polar Regions, and also, though on a much smaller scale, extending up mountain slopes from the warm lowlands to the alpine conditions of high elevations or altitudes.
Thus, horizontal sequence of biomes between equator and pole is repeated more or less exactly in a vertical direction, along the slopes of mountains (Fig. 4.20). For example, on a high mountain in the tropics, the sequence of biomes from mountain base to snowline is the tropical rain forest, deciduous forest, coniferous forest, and low herbaceous growths (mosses and lichens).
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The farther north a mountain is situated, the more northern a biome covers its base and the fewer biomes cover its slopes. For example, in the taiga (northern coniferous forest biome) the foot of a mountain is coniferous forest and the only other biome higher along the slopes is the zone of low shrubby plants. Conditions above timber line on high mountains resemble those of the tundra with some differences in lengths of day and night, temperatures, and atmospheric pressures.
The vegetation is similar in general appearance and in mountains of the temperate zone both vegetation and much of the fauna may consist of species related to those in the arctic. Ptarmigan and varying hares, related to arctic hares and also turning white during winter, extend far south of the tundra in alpine environments. Alpine insects are often closely related to arctic species.
On upper parts of very high tropical mountains, even the general aspect of fauna and flora is like that of the arctic tundra but the species are more distinct. In this way, the terrestrial habitat zones which are spread over thousands of miles latitudinally are telescoped altitudinally into a few thousand feet.
