The tundra is a cold, windy, dry region. The tundra is located in the Northern Hemisphere just south of the polar ice caps in Alaska, Canada, Greenland, Iceland, Scandinavia, and Russia. In the Southern Hemisphere, the region that would be the tundra is covered by oceans. The tundra is one of the larges biomes, making up almost 10 percent of the Earth's surface. However, fewer organisms live in the tundra than in any other biome. The lack of biodiversity makes tundra ecosystem very fragile and unstable if disturbed.
Like the desert, the tundra receives little precipitation. The tundra usually receives less than 25 cm of precipitation each year. The main difference between deserts and tundra is temperature. In the tundra, air temperatures rarely reaches above 10 degrees Celsius, even in the summer. Most precipitation falls as ice and snow. Temperatures, therefore, are the limiting factor in the tundra.
Summer days are long and cool. Only the top layer, or active zone, of soil thaws during the summer months. The active zone may be as thin as 8 cm. Beneath the active zone, the soil never thaws. The frozen soil below the active zone is called permafrost. A dense mat of mosses, grasses, and other plant life covers the active zone during summer. This mat keeps the ground insulated and prevents the permafrost from melting.
Because of the short growing season and low temperatures, tundra vegetation does not recover from disruption as quickly as does vegetation in other biomes. Tracks from wagons that crossed the tundra 100 years ago are still visible in some areas.
The tundra does receive a small amount of rain in the summer months. The rain cannot drain through the permafrost. Instead, the water collects at the surface, forming bogs, marshes, ponds, and small streams. These areas serve as the breeding grounds for insects such as mosquitoes and black flies. These insects are an important link in the food web of the tundra. The permafrost is therefore an important factor in the stability of a tundra ecosystem.
The summer growing season lasts only 60 days. The most common tundra plants are mosses, shrubs, grasses, lichens, and small, colorful wildflowers. Tundra plants tend to be small and grow very close to the ground's surface. Trees that grow in the tundra such as willow and alder are much smaller than their relatives in warmer climates. In fact, tundra trees are usually less than 1 m tall are are more like shrubs than trees. These plants are dwarfed by the short growing season, by the limited space for roots to grow, and by strong polar winds.
Many of the animals that live in the tundra are seasonal visitors. Season travel is called migration. Many species of birds migrate to the tundra to breed. There are fewer predators in the tundra, which makes it a safer place than most to raise young. Migratory birds feed on abundant flies and mosquitoes. The birds, in turn, serve as a food source for migratory predators such as the Arctic fox. Small herbivores are also common, but there are no reptiles or amphibians.
Caribou is a large migratory mammal of the tundra. Caribou have some adaptations that enable them to live in this environment. First, caribous have a thick coat. Their hairs are filled with air which acts as an insulator, reducing the loss of body heat. The second adaptation is that caribou also have wide hooves to help them move easily through snow or on the muddy ground in warmer months. Caribou feed on lichens. Lichens are sensitive to pollution. Because of the increase pollution, lichens grow very slowly, which in turn have decreased the migration of caribou.
Musk oxen, coastal polar bears, and wolverines are other permanent members of the tundra community.