Taiga, also known as theboreal forest, is a biome characterized by coniferous forests.
Taiga is the world's largest terrestrial biome and covers: in North America most of inland Canadaand Alaska as well as parts of the extreme northern continental United States; and in most ofSweden, Finland, inland and northern Norway, much of Russia, northern Kazakhstan, northern Mongolia, and northern Japan.
The term boreal forest is sometimes, particularly in Canada, used to refer to the more southerly part of the biome, while the term taiga is often used to describe the more barren areas of the northernmost part of the taiga approaching the tree line.
Taiga is the world's largest land biome, and makes up 29% of the world's forest cover;[2] the largest areas are located in Russia and Canada. The taiga is the terrestrial biome with the lowest annual average temperatures after the tundra and permanent ice caps. However, extreme minimums in the taiga are typically lower than those of the tundra. The lowest reliably recorded temperatures in the Northern Hemispherewere recorded in the taiga of northeastern Russia. The taiga or boreal forest has a subarctic climate with very large temperature range between seasons, but the long and cold winter is the dominant feature. This climate is classified as Dfc, Dwc, Dsc, Dfd and Dwd in theKöppen climate classification scheme,[3] meaning that the short summer (24-hr average 10 °C or more) lasts 1–3 months and always less than 4 months. There are also some much smaller areas grading towards the oceanic Cfc climate with milder winters, whilst the extreme south and (in Eurasia) west of the taiga reaches into humid continental climates (Dfb, Dwb) with longer summers. The mean annual temperature generally varies from -5 °C to 5 °C,[4] but there are taiga areas in eastern Siberia and interior Alaska-Yukon where the mean annual reaches down to -10 °C.[5][6] According to some sources, the boreal forest grades into a temperate mixed forest when mean annual temperature reaches about 3 °C.[7] Discontinuous permafrost is found in areas with mean annual temperature below 0 °C, whilst in the Dfdand Dwd climate zones continuous permafrost occurs and restricts growth to very shallow-rooted trees like Siberian larch. The winters, with average temperatures below freezing, last five to seven months. Temperatures vary from −54 °C to 30 °C (-65 °F to 86 °F) throughout the whole year. The summers, while short, are generally warm and humid. In much of the taiga, -20 °C would be a typical winter day temperature and 18 °C an average summer day.
external image 220px-Talkessel_von_Werchojansk.JPGexternal image magnify-clip.pngThe taiga in the river valley nearVerkhoyansk, Russia, at 67°N, must deal with the coldest winter temperatures in the northern hemisphere, but the extreme continentality of the climate gives an average daily high of 22 °C in July.
The growing season, when the vegetation in the taiga comes alive, is usually slightly longer than the climatic definition of summer as the plants of the boreal biome have a lower threshold to trigger growth. In Canada, Scandinavia and Finland, the growing season is often estimated by using the period of the year when the 24-hr average temperature is 5 °C or more.[8] For the Taiga Plains in Canada, growing season varies from 80 to 150 days, and in the Taiga Shield from 100 to 140 days.[9] Some sources claim 130 days growing season as typical for the taiga.[10] Other sources mention that 50–100 frost-free days are characteristic.[11] Data for locations in southwest Yukon gives 80–120 frost-free days.[12] The closed canopy boreal forest in Kenozyorsky National Parknear Plesetsk, Arkhangelsk Province, Russia, on average has 108 frost-free days.[13] The longest growing season is found in the smaller areas with oceanic influences; in coastal areas of Scandinavia and Finland, the growing season of the closed boreal forest can be 145–180 days.[14]The shortest growing season is found at the northern taiga–tundra ecotone, where the northern taiga forest no longer can grow and the tundra dominates the landscape when the growing season is down to 50–70 days,[15][16] and the 24-hr average of the warmest month of the year usually is 10 °C or less.[17] High latitudes mean that the sun does not rise far above the horizon, and lesssolar energy is received than further south. But the high latitude also ensures very long summer days, as the sun stays above the horizon nearly 20 hours each day, with only around 6 hours of daylight occurring in the dark winters, depending on latitude. The areas of the taiga inside the Arctic circle have midnight sun in mid-summer and polar night in mid-winter.
external image 220px-Helvetinj%C3%A4rvi.JPGexternal image magnify-clip.pngLakes and other water bodies are very common. The Helvetinjärvi National Park, Finland, situated in the closed canopy taiga (mid-boreal to south-boreal) [18] with mean annual temperature of 4 °C.[19]
The taiga experiences relatively low precipitation throughout the year (generally 200–750 mm annually, 1,000 mm in some areas), primarily as rain during the summer months, but also as fogand snow. This fog, especially predominant in low-lying areas during and after the thawing of frozen Arctic seas, means that sunshine is not abundant in the taiga even during the long summer days. As evaporation is consequently low for most of the year, precipitation exceeds evaporation, and is sufficient to sustain the dense vegetation growth. Snow may remain on the ground for as long as nine months in the northernmost extensions of the taiga ecozone.[20]
In general, taiga grows to the south of the 10 °C July isotherm, but occasionally as far north as the 9 °C July isotherm.[21] The southern limit is more variable, depending on rainfall; taiga may be replaced by forest steppe south of the 15 °C July isotherm where rainfall is very low, but more typically extends south to the 18 °C July isotherm, and locally where rainfall is higher (notably in eastern Siberia and adjacent northern Manchuria) south to the 20 °C July isotherm. In these warmer areas the taiga has higher species diversity, with more warmth-loving species such asKorean Pine, Jezo Spruce, and Manchurian Fir, and merges gradually into mixed temperate forestor, more locally (on the Pacific Ocean coasts of North America and Asia), into coniferous temperate rainforests.
The area currently classified as taiga in Europe and North America (except Alaska) was recently glaciated. As the glaciers receded they leftdepressions in the topography that have since filled with water, creating lakes and bogs (especially muskeg soil) found throughout the taiga.
Taiga, supports a large range of animals. Canada's boreal forest includes 85 species of mammals, 130 species of fish, and an estimated 32,000 species of insects. Insects play a critical role as pollinators, decomposers, and as a part of the food web. Many nesting birds rely on them for food. The cold winters and short summers make the taiga a challenging biome forreptiles and amphibians, which depend on environmental conditions to regulate their body temperatures, and there are only a few species in the boreal forest. Some hibernate underground in winter.
The taiga is home to a number of large herbivorous mammals, such as moose andreindeer/caribou. Some areas of the more southern closed boreal forest also have populations of other deer species such as the elk (wapiti) and roe deer. There is also a range of rodentspecies including beaver, squirrel, mountain hare, snowshoe hare, and vole. These species have evolved to survive the harsh winters in their native ranges. Some larger mammals, such as bears, eat heartily during the summer in order to gain weight, and then go into hibernation during the winter. Other animals have adapted layers of fur or feathers to insulate them from the cold.
A number of wildlife species threatened or endangered with extinction can be found in the Canadian boreal forest, including woodland caribou,American black bear, grizzly bear, and wolverine. Habitat loss, mainly due to logging, is the primary cause of decline for these species.
Due to the climate, carnivorous diets are an inefficient means of obtaining energy; energy is limited, and most energy is lost between trophic levels. Predatory birds (owls and eagles) and other smaller carnivores, including foxes and weasels, feed on the rodents. Larger carnivores, such as lynx and wolves, prey on the larger animals. Omnivores, such as bears and raccoons are fairly common, sometimes picking through human garbage.
More than 300 species of birds have their nesting grounds in the taiga.[32] Siberian Thrush, White-throated Sparrow, and Black-throated Green Warbler migrate to this habitat to take advantage of the long summer days and abundance of insects found around the numerous bogs and lakes. Of the 300 species of birds that summer in the taiga only 30 stay for the winter. These are either carrion-feeding or large raptorsthat can take live mammal prey, including Golden Eagle, Rough-legged Buzzard (also known as the Rough-legged Hawk), and Raven, or else seed-eating birds, including several species of grouse and crossbills.

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