There are two types of tundra in the world, Arctic and Alpine. The arctic tundra is at the top of the world around the North Pole. The tops of tall cold mountains are alpine tundra. The most distinctive characteristic of the tundra soil is its permafrost, a permanently frozen layer of ground often 2000 feet thick. Shallow rooted tundra plants and microorganisms grow in the permafrost. Animals are adapted to handle cold winters and to breed and raise young quickly in the short summers. Average yearly temperatures range from -70 degrees F to 20 degrees F.
Artic wildlife is circumpolar (surrounding or near either pole of the earth), the same or closely related species are found around the world. The variety of animal life is also limited in the challenging environment. Musk-ox, caribou, and reindeer are the dominant large grazers, feeding on grass, sedge, lichen, and willow. Arctic hare, or snowshoe rabbit, and lemming feed on grass and sedge. Predators include the wolf, artic fox, and snowy owl. Polar bears, and sometimes brown bears are seen. Many birds nest in the tundra shrubbery in summer, migrating to milder climates before the winter season sets in. Invertebrate life is scarce, but insects such as black flies and mosquitoes are abundant. Alpine animal life includes the mountain goat, big-horned sheep, pika, marmot, and the ptarmigan, a grouselike bird. Flies are scarce but butterflies, beetles, and grasshoppers are abundant.
The tundra ecosystem is extremely sensitive to disturbance with little ability to restore itself. Disruption of vegetative cover causes permafrost to melt deeply, causing collapse of ground and loss of soil. Automobile tracks cause deep gullies that persist for years. The tundra wildlife is vulnerable to habitat destruction, to overhunting, and to extinction through loss of any of the animal or plant species that make up the fragile, highly individual tundra community of life.
Typical arctic vegetation comprises cotton grass, sedge, and dwarf heath, together with associated mosses and lichens. These plant communites are adapted to sweeping winds and to soil disturbance from frost heaves. They carry on photosynthesis at low temperatures, low light intensities, and long periods of daylight. Alpine plant communities consist of mat-making and cushion-forming plants. These plants are rare in the Arctic. These plants are adapted to gusting winds, heavy snows, and widely ranging temperatures. They carry on photosynthesis under brilliant light in short periods of daylight.
Cushion Plants Many tundra plants, such as this one, are called cushion plants which means they grow in a low, tight clump and look like a little cushion. Cushion plants are more common in the tundra where their growth habit helps protect them from the cold.
Cotton Grass Cotton grass has seeds that are spread out across the tundra when their wings are caught by the wind.
In relatively well-drained locations, the periodic freezing and thawing of the soil forms cracks in the ground in regularly patterned polygons. Poorly drained areas produce irregular landforms such as hummocks, or knolls, frost boils, and earth stripes. Thawing of slopes in the summer may move soil downslope to produce solifluction, or "flowing soil" terraces. All of these patterns, produced on the arctic tundra, also appear on a smaller scale on the alpine tundra. Common to the alpine tundra is bare rock-covered ground, called fell-fields, supporting a growth of lichens. The numerous smaller habitats provided by these landforms give variety to the tundra landscape.
Frostbite is another problem in areas of extreme cold. Frostbite is caused by exposure to severe cold. Frostbite occurs more often when the wind is blowing, quickly taking heat from the body. The ears, cheeks, nose, toes, and fingers are frostbitten the most frequently. When the part of the body is exposed to cold, the blood vessels constrict. When this occurs the blood supply to the chilled parts decreases and the tissues don't get the warmth they need.