tundra

The tundra is a cold, dry biome characterized by a permanently frozen subsoil called permafrost and a treeless plain. Mean annual temperatures are well below freezing in most areas, with short, cool summers. Precipitation is low, usually under 250 mm per year, most as snow. The tundra occurs at high northern latitudes around the Arctic Circle and on high mountain tops (alpine tundra).

Soils are thin and acidic; an active summer layer thaws briefly but remains frozen for most of the year. Low temperatures and a short growing season limit plant life to low-lying vegetation: lichens, mosses, grasses, sedges, and dwarf shrubs. Trees do not establish, because and the ground remains unfriendly to deep root growth.

There are two main tundra types: Arctic tundra and alpine tundra. Arctic tundra encircles the northern continents; alpine tundra occurs at high elevations worldwide. Vegetation is adapted to wind, cold, and freeze-thaw cycles, often forming patterned ground and peat bogs in wetter areas.

Animal life is adapted to scarcity of food and extreme cold. Common inhabitants include caribou or reindeer, muskox, Arctic fox, lemmings, and various migratory birds. Insects proliferate briefly in summer. Many species migrate or hibernate to survive winter.

Human activity is limited but present, with indigenous peoples practicing subsistence hunting and reindeer herding, and mining or energy exploration in some regions. The tundra is sensitive to climate change: warming prompts permafrost thaw, shrub expansion, and changes in ecosystem structure and albedo, with broader climate feedbacks.