The Tundra
The tundra biome is one of the largest biomes in the world, covering about 20% of the Earth's landmasses. The Arctic tundra is a biome where the tree growth is limited by temperatures that can range from a glacial low of -46 degrees Celsius (-71.5 degrees Fahrenheit) in the winter, to a balmy high of 12 degrees Celsius (59 degrees Fahrenheit) in the summer. Even during the summer, however, the temperature can still drop to below freezing at night. There are three types of tundra: Arctic, Antarctic, and Alpine. The Alpine tundra occurs in northern mountain ranges ringing the Arctic Circle. Antarctic tundras occur on Antarctica and several Antarctic and sub-Antarctic islands. The Arctic tundra occurs in areas north of the taiga. The ecotone, or ecological boundary region, between the tundra and the forest is known as the timberline, or tree line. For most of the year, the Arctic tundra is frozen. Then, once the permafrost thaws to create lakes and marshes, millions of birds migrate there to feast on the suddenly abundant insects. However, overall biodiversity of the Arctic tundra remains low. There are only 48 animal species that live in the Arctic tundra year round: caribou (reindeer), musk ox, arctic hares, arctic foxes, snowy owls, lemmings, and, usually staying near ocean-fed bodies of water, polar bears.