Some five million acres of tundra stretch across Northern America, Northern Europe and Siberia. Although there is variation from place to place within the biome, temperature, precipitation, and evaporation are characteristically low, the warmest months averaging below 10°C and the wettest with about 25 mm of precipitation. Despite the small amount of precipitation, water is usually not a limiting factor because the rate of evaporation is also very low.
The ground usually remains frozen except for the uppermost 10 to 20 cm, which thaw during the brief summer seasons. The permanently frozen deeper soil layer is called permafrost. The permafrost line which may exist at a depth of a few centimeters to several meters is the ultimate limit of plant root growth, but the immediate control is the depth to which soil is thawed in summer.
The rather thin carpet of vegetation of tundra biome includes few species: grasses and sedges are characteristic of numerous marshes and poorly drained areas, but large areas consist of ericaceous heat plants (bilberries and dwarf huckleberries), low flowering herbs, and lichens. Perhaps the most characteristic arctic tundra plant is the lichen known as ”reindeer moss” (Cladonia).
The animals that have adapted to survive in the tundra are caribou or reindeer, the arctic hare, arctic fox, polar bear, wolves, lemmings, snowy owls, ptarmigans and during the summer, swarms of flies, mosquitoes and a host of migratory birds.
Further, certain animals such as caribou and reindeer are highly migratory because there is not enough vegetation produced in any one local area to support them. Though tundra’s are barren areas yet a surprisingly large number of organisms have become adapted to survive the cold.
During the long daylight hours of the brief summer, the rate of primary production is quite high. The production from the vegetation on the land, from the plants in the many shallow ponds that dot the landscape and from the phytoplankton in the adjacent Arctic Ocean provides enough food to support a variety of resident mammals and many kinds of migratory birds and insects.
Diversity is very low, and despite the extreme hardiness of the tundra organisms, their growth rate tends to be very low, and the community as a structural unit is exceedingly vulnerable.
Moreover, Alpine tundra is quite similar to some of Arctic tundra, but in the absence of permafrost and in the growing season, mosses and lichens are less prominent, flowering plants more so.