Farthest north in Eurasia, North America, and their associated islands, between th taiga and the permanent ice, occurs the open, often boggy community known as th tundra. This is an enormous biome, extremely uniform in appearance that covers a fifth of the earth's land surface. Trees are small and are mostly confinei to the margins of streams and lakes; in general, the tundra is dominated by scatters patches of grasses and sedges (grasslike plants), heathers, and lichens, with dense stands in wet places.

Annual precipitation in the tundra is low, usually less than 25 centimeters, am the water is unavailable for most of the year because it is frozen. During the brie arctic summers, water sits on frozen ground, and the surface of the tundra is oflei extremely boggy then. Permafrost, or permanent ice, usually exists within a meter of the surface.

 The tundra receives little precipitation, usually less than 25 centimeters per year, but the water is often trapped near the surface by the widespread permafrost. For that reason, the undra is often boggy.



As in the taiga, the herbs of the tundra are perennials that grow rapidly during the brief summers, using food stored underground. Large grazing mammals, includ. ing musk-oxen, caribou, reindeer, and carnivores such as wolves, foxes, and lynx, Uvf in the tundra, which teems with life in the short summer. Lemmings, a genus oj small rodents, are animals of the tundra, and their populations rise rapidly and then crash on a long-term cycle, with important effects on the populations of the animals that prey on them.