THE NATURAL ENVIRONMENT

Geography 101

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LIFE

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Biomes

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Temperate

Cold

Hawai'i

Cold Climate Biomes

Long, cold winters and short, cool summers characterize high latitude biomes. Plants must be able to withstand cold, drought, high wind, and a short growing season. Soils are usually poorly developed and often acidic. Mountain zones merit special consideration, but are included here as higher elevations often have harsh climates similar to high latitude areas.

Taiga

Taiga, also called northern coniferous forest or boreal forest, occurs only in the northern hemisphere. These expansive northern forests fill almost all of the land area between about 50° and 70° North latitude. Taiga does not occur in the southern hemisphere simply because very little land area exists at the appropriate latitudes. Coniferous evergreens, such as spruce, pine, fir, and larch dominate these cold forests. Unlike the highly diverse tropical forests, one or two species may dominate hundreds of square kilometers of taiga

Tree adaptations to the harsh climate include a conical shape to shed snow, rolled needle leaves to reduce moisture loss and retention of leaves through the winter so that they can quickly photosynthesize whenever temperature and moisture conditions permit. Animals, too, have adapted. Some, like bears, hibernate to avoid most of the winter. Others, like the fox and ermine, have very thick fur as insulation. Others, like squirrels, store food to survive the winter months.

Today, vast tracts of untouched taiga still remain, mostly in Russia. In the US and Canada, large areas have been cleared by logging, with some replanting as tree farms. A major environmental threat comes from acid rain. Polluted air from industrialized areas to the south is carried over the taiga where it reacts with rainwater to produce sulfuric and nitric acids. These acids rain out over wilderness areas, killing lakes and blighting forests.

Tundra

Tundra is a Russian word (as is taiga) that means "treeless plain." North of about 70° latitude conditions are too harsh to support trees. As you approach this latitude, the taiga gradually thins out, trees become more scattered and smaller and eventually disappear altogether. This point is called the tree line, north of which lies tundra.

Plants of the tundra are mostly low shrubs, grasses, lichens, and mosses. They have developed special adaptations to extreme conditions, such as:

1. Most of their mass lies below ground where it is protected from the howling, icy winds.
2. They seldom grow more than 15 cm (6 inches) high because strong winds bounce an abrasive load of ice crystals along the surface, eroding away any plant matter that juts out.
3. Many of the plants have hollow stems that retain heat inside and require less energy to produce. They may also have dark colors to decrease albedo or fuzzy surfaces to trap heat.
4. The seeds are generally very hardy and the tissue remains viable in frozen permafrost for a long, long time. Russian scientists grew arctic campion flowers from the fruit of a plant that died in Siberia 32,000 years ago.

Animal survival strategies include migration, especially tundra birds like the Arctic tern which flies 34,000 kilometers (21,000 miles) each year on its round trip migration to Antarctica. Polar bears have "optical fiber" fur that transmits sunlight directly to the skin where it is absorbed. The arctic wood frog freezes so solid that its heart stops and all brain function ceases. When spring comes, it thaws out and hops off as if nothing had happened. Lemmings periodically undertake large-scale migrations, apparently in response to overpopulation, that can result in mass drownings.

Although no large human populations exist in tundra, the biome is, nonetheless, affected by development. Oil and natural gas pipelines cross tundra affecting the migration of caribou. Radioactive fallout from Russia's Chernobyl meltdown showed up in tundra-grazing reindeer milk in northern Scandinavia. The rain of pollution from northern factories has concentrated in slow growing tundra plants, driving some to extinction.

Mountain Zones

Mountains are a special case in biogeography. Going up a high tropical mountain is similar to moving from tropical areas, to temperate areas, to polar areas, because temperature decreases with elevation. Also, the rainfall amount can vary greatly with elevation and with exposure such as windward or leeward and south or north facing slope. Thus, mountain climates, and their associated plant and animal communities, can vary greatly over small distances.

The interplay between elevation, latitude, and vegetation can be summarized in a simplified diagram. Recall from above that the tree line forms at about 70° N at sea level as shown in the diagram. As you move south into warmer climates, a tree line can also be found at successively higher elevations. At 60° N, it has risen to around 1000 meters (3000 feet). At 40° N (central Rocky Mountains), it lies at about 3300 meters (11,000 feet). At 20° N (Central America), the tree line is found at about 4200 meters (14,000 feet) and in equatorial mountains, it occurs at about 5000 meters (16,000 feet) elevation.

Above these mountain tree lines, the environment is too harsh to support trees and tundra-like plants called alpine vegetation prevail. Although alpine plants grow in cold conditions and look similar to tundra plants, the environments have significant differences. Tundra lies near sea level on the fringes of the Arctic Ocean. Alpine vegetation, on the other hand, grows at high elevations where the air pressure is much lower and the ultraviolet radiation exposure is much greater. Tundra also lies north of the Arctic Circle, meaning that it is exposed to 24 hours of daylight during summers and 24 hours of darkness during winters. Alpine areas, however, have a much more equal division of daylight and darkness. Equatorial mountains, in fact, experience 12 hours of each throughout the year. The difference between daytime and nighttime temperature is also generally much greater in high mountains than sea level tundra.

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