In physical geography, tundra (/ˈtʌndrə, ˈtʊn-/) is a type of biome where tree growth is hindered by frigid temperatures and short growing seasons.

[3] Tundra vegetation is composed of dwarf shrubs, sedges, grasses, mosses, and lichens.

The ecotone (or ecological boundary region) between the tundra and the forest is known as the tree line or timberline.

[2] The polar tundra is home to several peoples who are mostly nomadic reindeer herders, such as the Nganasan and Nenets in the permafrost area (and the Sami in Sápmi).

Instead, bare and sometimes rocky land can only support certain kinds of Arctic vegetation, low-growing plants such as moss, heath (Ericaceae varieties such as crowberry and black bearberry), and lichen.

During the summer, temperatures rise somewhat, and the top layer of seasonally-frozen soil melts, leaving the ground very soggy.

The thawing of the permafrost in a given area on human time scales (decades or centuries) could radically change which species can survive there.

[13] It also represents a significant risk to infrastructure built on top of permafrost, such as roads and pipelines.

In locations where dead vegetation and peat have accumulated, there is a risk of wildfire, such as the 1,039 km2 (401 sq mi) of tundra which burned in 2007 on the north slope of the Brooks Range in Alaska.

However, some portions of the continent, particularly the Antarctic Peninsula, have areas of rocky soil that support plant life.

[21] More recent approaches have since recognized it as a temperate grassland, restricting southern tundra to coastal Antarctica and its islands.

[28] The flora is adapted to the harsh conditions of the alpine environment, which include low temperatures, dryness, ultraviolet radiation, and a short growing season.

[29] The cold limit generally meets the EF climates of permanent ice and snows; the warm-summer limit generally corresponds with the poleward or altitudinal limit of trees,[30] where they grade into the subarctic climates designated Dfd, Dwd and Dsd (extreme winters as in parts of Siberia), Dfc typical in Alaska, Canada, mountain areas of Scandinavia, European Russia, and Western Siberia (cold winters with months of freezing).

[31] Despite the potential diversity of climates in the ET category involving precipitation, extreme temperatures, and relative wet and dry seasons, this category is rarely subdivided, although, for example, Wainwright, Alaska can be classified ETw and Provideniya, Russia ETs, with most of the rest of the tundra fitting into the ETf subcategory.

Rainfall and snowfall are generally slight due to the low vapor pressure of water in the chilly atmosphere, but as a rule potential evapotranspiration is extremely low, allowing soggy terrain of swamps and bogs even in places that get precipitation typical of deserts of lower and middle latitudes.