The tundra biome is characterized by extremely low temperatures throughout most of the year, along with a short summer season, during which plants and animals reproduce. The tundra biome cannot support many plants. The majority of flora consists of low growing plants, along with some stunted and scattered trees. Plants and animals are adapted to survive in the harsh conditions of tundra. There exist three types of tundra which are named based on the region of the world they´re located: the arctic tundra, Antarctic tundra and alpine tundra. These biomes share common features; however, each of them conserves distinct characteristics which make them unique.
In the tundra biome, tree growth is hindered by cold temperatures and short growing seasons, ranging from 40-60 days. All tundra biomes share a layer of permanent frozen soil (permafrost) which makes it difficult for plants and trees to grow with the greater part of tundra flora consisting of mosses, lichens, sedges, grasses and low growing shrubs. The winter season is usually long with varied temperatures, depending on the type of tundra. Animals are adapted to cold winter temperature, and they usually breed during the summer.
Arctic tundra is found in the Northern Hemisphere, encircling the North Pole, and is delimited by the tiga forest in the south. The transition between tiga and tundra is characterized by an open landscape with patches of stunted trees and dense thickets of shrubs. The arctic tundra is characterized by treeless landscape with extremely cold winters and short cool summers. The temperature in the arctic biome is determined by the angle of the Sun with respect to the Earth. A layer of permafrost, which persists throughout the year, prevents the growth of plants; however, there are some plant species that are able to resist the cold climate.
The mean average temperature vary according to location, with temperatures of -12° C (10° F) in Point Barrow, Alaska located at (71.3 ° N) to -28° C (-18° F) at the Northern region of Greenland (71° N). Temperature for the warmest months in the arctic tundra ranges from 3-12° C (37- 57° F). Annual precipitation varies from about 25 cm (10 inches) in the southern regions to approximately 4.5 cm (1.7 inches) in the northern Polar Regions; however, heavy rain of about 110 cm (43 inches) may persist in subarctic maritime regions. Winds ranging from 48-97 km/h (30-60 miles/h) are very common in the arctic tundra.
The landscape of the arctic tundra remains frozen throughout much of the year, making it impossible for trees to grow. Bare and, in some parts, rocky land support low growing plants, including moss, and lichen. During the summer months, the permafrost layer melts, leaving a very soggy land. During these months, the arctic tundra is covered throughout most of the land with lakes, bogs, marshes and streams. Vegetation in the arctic tundra reflect the typically tundra landscape with plant communities having canopies that extend for more than 3 meters (10 feet) high to deserted Polar Regions, where vegetation is scarce and is dominated by lichens, herbs, algae, fungi and mosses.
Animal biodiversity in the arctic tundra accounts to approximately 55 mammal species with only a few of them making large populations, although, millions of birds migrate each year. There are few fish species, including the flatfish. Some of the most prominent animals in the arctic tundra include the musk ox, the caribou, arctic fox, arctic hare, lemmings, snowy owl and the polar bear which can only be spotted in the northern extremes of the tundra. Due to the harsh climate, human activity is very rare in the arctic tundra.
The Antarctic tundra occurs in the Antarctic continent and a number of islands, including the South Sandwich Islands, Kerguelen Islands and South Georgia Islands and sub Antarctic islands, such as the Auckland Islands, Bounty Islands, Macquarie Island, Antipodes Islands and Campbell Island group. The greatest part of Antarctica is extremely cold for vegetation to grow, and most of the continent is covered with ice, however, some areas of the continent, such as the Antarctic Peninsula presents the mildest climate, allowing a few flora species, such as lichens, mosses, liverworts and terrestrial and aquatic algae, along with the only two flowering plants (Antarctic Hair grass and Antarctic pearlwort), to grow in the exposed rocky and sandy regions of the Peninsula.
Unlike the Arctic tundra, the Antarctic tundra lacks animal diversity due to the extremely cold environment and isolation from other continents. Sea birds and Sea mammals, including seals and penguins, inhabit the shorelines. Other mammals, such as cats and rabbits have been introduced by humans in some of the sub Antarctic islands. Species characteristic of the Macquarie Island include the royal penguin, the antipodean albatross and the only subantarctic orchid plant, which is listed as an endangered species by UNESCO.
The alpine tundra occurs in most mountainous regions of the world at altitudes that prevent the growth of trees. The alpine temperature varies according to location, ranging from below freezing to 10-15° C (50-59° F). The annual precipitation average 50 cm (20 inches) and is often in the form of snow accompanied by strong dry winds. The alpine tundra vegetation, which has developed methods of adaptation in such harsh environment, includes small growing shrubs, mosses, sedges, forbs, lichens, heaths and perennial grasses with some scarce trees. Animals found in the alpine biome include the nutcracker, hoary marmot, pika and the chickaree, although some animals are only found in certain alpine biomes, including the mountain goat in North America and llamas and chinchilla in the Andes in South America.
Global warming represents a serious threat for the Antarctic tundra. The melting of the permafrost is likely to determine the survival of some species. Even a few centimeters of permafrost thaw could alter the habitat of some animal and plant species. Larger melting plaques of permafrost could expose vast regions of land to the wind, affecting the distribution of plant and animal species. According to the National Center for Atmospheric Research, permafrost melting releases greenhouse gases (carbon dioxide and methane) into the atmosphere.