The locations of areas of Tundra are limited to colder places, including northern Greenland, Alaska, Canada, Europe, and Russia. There are two different kinds of Tundra, arctic and alpine, the difference between them being that Alpine Tundras are located at high altitudes, and lack trees, that can't grow at such high altitudes. The temperate of Tundras are always cold, with a constantly frozen layer of permafrost. The things that live in Arctic Tundra consist of animals like polar bears, caribou, musk ox, grey wolves, lemmings, rabbits, squirrels, birds like penguins, falcons, ravens, terns, and loons, and fish that live in icy rivers like trout and salmon. Some animals that live in Alpine Tundra are elk, pika, and marmots, and some birds include white-tailed parmigan and the grouse. Some plants that live in tundra are shrubbery, lichen, moss, and flowers, because of the frozen layer of permafrost, roots of plants can't go deep into the ground, limiting the plant species that can survive there. One thing that's threatening the Tundra is global warming, threatening to shorten winters and melt part of the layer of permafrost.