Tundra describes an area where there are few if any trees and the temperatures are cold. The term tundra normally brings to mind the area that occurs in the northern hemisphere above the tree line in places, such as Siberia, Canada and Alaska. A tundra also occurs in mountainous regions where the high elevation and cold make the growth of trees impossible. This type of tundra is known as an alpine tundra. In the Antarctic, the tundra exists near the coast but supports only two plant species and there are no land animals that live there. Plant and animal life on the tundra have had to adapt to harsh conditions, and few animals live on the northern tundra year-round.
The Arctic tundra is subject to summers that are fleetingly short and winters that are very long. In this part of the world the ground is always in a frozen state. This is known as permafrost. Above it is a layer near the surface of the ground that will thaw only when the warmer weather comes in the summer. This active layer's thickness depends on just how far north you go on the tundra, with the southern portions of the tundra having a thicker layer than the northern ones. Since nothing can penetrate this frozen soil, trees are unable to put down roots--this results in the distinct lack of any large trees. Melting snow on the tundra actually will result in pools of surface water since the water cannot make it through the permafrost and into the ground. At certain latitudes on the tundra, the sun will not be seen for as long as two months due to the region's proximity to the pole. The average winter temperatures on the Arctic tundra are in the range of 20 to 30 below zero, while it seldom tops 50 degrees F in the summer. This northern tundra experiences low precipitation, with just 6 to 10 inches falling each year. The winds are somewhat constant and gust steadily at 20 to 40 miles an hour.
Many species of birds will spend their summers on the tundra but then migrate south once the cold weather begins to manifest itself. Birds from all over the world show up on the tundra to feast on the incredible supply of bugs, plants and different species which multiply during the tundra's warm months when the hours of daylight are increased. Some birds will travel as far as thousands of miles to come to the tundra where they will breed, eat, and then leave before returning the next year. Geese, loons, plovers, terns, swans, ducks, different songbirds and shore birds all find their way to the tundra. Snowy owls, ravens, ptarmigans and a bird called a redpoll are among the few species hardy enough to spend the whole year in these harsh conditions.
The largest predator on the tundra is the polar bear, which spends some time there and the rest on the pack ice off shore searching for seals to eat. The musk ox is a bovine species with an extremely thick coat that allows it to survive the cold winters. The caribou, also called reindeer, has a coat featuring hollow hairs that trap heat next to the skin; huge herds of caribou traverse the tundra. The arctic fox and the snowshoe hare also live on the tundra, with both of these animals having the ability to change the color of their fur from brownish in the warm months to white when it gets cold so that they are camouflaged all the time. The grizzly bear is a year-round resident of the tundra but it will hibernate to avoid the long winters when food is scarce as will the ground squirrel. Lemmings, a relative of the vole, are a smallish rodent that stays active throughout the tundra year, existing beneath the snow on grasses it finds as it burrows.