BIOMES

BIOMES

A biome is a large, distinctive complex of plant communities created and maintained by climate.

How many biomes are there?

A study published in 1999 concluded that there are 150 different "ecoregions" in North America alone. But I shall cast my lot with the "lumpers" rather than the "splitters" and lump these into 8 biomes:

• tundra

• taiga

• temperate deciduos forest

• scrub forest (called chaparral in California)

• grassland

• desert

• tropical rain forest

A number of climatic factors interact in the creation and maintenance of a biome. Where precipitation is moderately abundant — 40 inches (about 1 m) or more per year — and distributed fairly evenly throughout the year, the major determinant is temperature. It is not simply a matter of average temperature, but includes such limiting factors as:

• whether it ever freezes;

• length of the growing season

If there is ample rainfall, we find 4 characteristic biomes as we proceed from the tropics (high temperatures) to the extreme latitudes (low temperatures). In order, they are:

• tropical rain forest or jungle

• temperate deciduous forest

• taiga

• tundra

Tropical Rain Forest

In the Western Hemisphere, the tropical rain forest reaches its fullest development in the jungles of Central and South America.

Characteristics:

• The trees are very tall and of a great variety of species.

• One rarely finds two trees of the same species growing close to one another.

• The vegetation is so dense that little light reaches the forest floor.

• Most of the plants are evergreen, not deciduous.

• The branches of the trees are festooned with vines and epiphytes (see the photo taken in the Luquillo National Forest of Puerto Rico).

Temperate Deciduous Forest

This biome occupies the eastern half of the United States and a large portion of Europe. It is characterized by:

• hardwood trees (e.g., beech, maple, oak, hickory) which

• are deciduous; that is, shed their leaves in the autumn.

• The number of different species is far more limited than in the jungle.

• Large stands dominated by a single species are common.

• Deer, raccoons, and salamanders are characteristic inhabitants.

• During the growing season, this biome can be quite productive in both natural and agricultural ecosystems.

Taiga

The taiga is named after the biome in Russia.

• It is a land dominated by conifers, especially spruces and firs.

• It is dotted with lakes, bogs, and marshes.

• It is populated by an even more limited variety of plants and animals than is the temperate deciduous forest.

• In North America, the moose is such a typical member that it has led to the name: "spruce-moose" biome.

• Before the long, snowy winter sets in, many of the mammals hibernate, and many of the birds migrate south.

• Although the long days of summer permit plants to grow luxuriantly, net productivity is low.

Tundra

At extreme latitudes, the trees of the taiga become stunted by the harshness of the subarctic climate. Finally, they disappear leaving a land of bogs and lakes.

• The climate is so cold in winter that even the long days of summer are unable to thaw the permafrost beneath the surface layers of soil.

• Sphagnum moss, a wide variety of lichens, and some grasses and fast-growing annuals dominate the landscape during the short growing season.

• Caribou feed on this growth as do vast numbers of insects.

• Swarms of migrating birds, especially waterfowl, invade the tundra in the summer to raise their young, feeding them on a large variety of aquatic invertebrates and vertebrates.

• As the brief arctic summer draws to a close, the birds fly south, and

• all but a few of the permanent residents, in one way or another, prepare themselves to spend the winter in a dormant state.

Temperate Rain Forest

• The temperate rain forest combines high annual rainfall with a temperate climate. The Olympic Peninsula in North America is a good example. An annual rainfall of as much as 150 inches (381 cm) produces a lush forest of conifers.

Grasslands

Grasslands are also known as prairie or plains. The annual precipitation in the grasslands averages 20 inches (~51 cm) per year. A large proportion of this falls as rain early in the growing season. This promotes a vigorous growth of perennial grasses and herbs, but — except along river valleys — is barely adequate for the growth of forests.

Desert

Annual rainfall in the desert is less than 10 inches (25 cm) and, in some years, may be zero. Because of the extreme dryness of the desert, its colonization is limited to

• plants such as cacti, sagebrush, and mesquite that have a number of adaptations that conserve water over long periods;

• Fast-growing annuals, whose seeds can germinate, develop to maturity, flower, and produce a new crop of seeds all within a few weeks following a rare, soaking rain.

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