Taiga or Boreal Forest

Introduction.The taiga or boreal forest exists as a nearly continuous belt of coniferous trees across North America and Eurasia. Overlying formerly glaciated areas and areas of patchy permafrost on both continents, the forest is mosaic of successional and subclimax plant communities sensitive to varying environmental conditions. Taiga is the Russian name for this forest which covers so much of that country. However, the term is used in North America as well.

Climate: The taiga corresponds with regions of subarctic and cold continental climate (Koeppen's Dfc, Dfd, and Dwd climate types). Long, severe winters (up to six months with mean temperatures below freezing) and short summers (50 to 100 frost-free days) are characteristic, as is a wide range of temperatures between the lows of winter and highs of summer. For example, Verkhoyansk, Russia, has recorded extremes of minus 90 Fand plus 90 F. Mean annual precipitation is 15 to 20 inches, but low evaporation rates make this a humid climate.

Vegetation: Needleleaf, coniferous (gymnosperm) trees are the dominant plants of the taiga biome. A very few species in four main genera are found: the evergreen spruce (Picea), fir (Abies), and pine (Pinus), and the deciduous larch or tamarack (Larix). In North America, one or two species of fir and one or two species of spruce are dominant. Across Scandanavia and western Russia the Scots pine is a common component of the taiga.

Broadleaf deciduous trees and shrubs are members of early successional stages of both primary and secondary succession. Most common are alder (Alnus), birch (Betula), and aspen (Populus).

Growthforms: The conical or spire-shaped needleleaf trees common to the taiga are adapted to the cold and the physiological drought of winter and to the short-growing season:

Soil: Podzolization occurs as a result of the acid soil solution produced under needleleaf trees. The main soil order associated with the taiga is spodosol.

Subclimaxes: Edaphic conditions result in sometimes extensive, persistent patches of vegetation other than spruce and fir:

  1. bogs (muskeg) occur in poorly drained, glacial depressions. Sphagnum moss forms a spongy mat over ponded water. Growing on this mat are species of the tundra such as cottongrass and shrubs of the heath family. Black spruce and larch ring the edge.
  2. Pine forests, in North America dominated by the jack pine (Pinus banksiana), occur on sandy outwash plains and former dune areas. These are low nutrient, droughty substrates not tolerated by spruce and fir.
  3. Larch forests claim the thin, waterlogged substrate in level areas underlain with permafrost. These forests are open with understories of shrubs, mosses and lichens. In Alaska stands of Larix larichina are localized phenomena, but in Siberia east of the Yenesei River the extreme continentality and nearly continuous permafrost give rise to vast areas dominated by Larix dihurica.

    Fauna: Fur-bearing predators like the lynx (Felis lynx) and various members of the weasel family (e.g., wolverine, fisher, pine martin, mink, ermine, and sable) are perhaps most characteristic of the boreal forest proper. The mammalian herbivores on which they feed include the snowshoe or varying hare, red squirrel, lemmings, and voles.

    Large herbivores are more closely associated with successional stages where there is more nutritious browse available and include elk or wapiti (Cervus elaphus, known as red deer in Europe) and moose (Alces alces, known as elk in Europe). The beaver (Castor canadensis), on which the early North American fur trade was based, is also a creature of early successional communities, indeed its dams along streams create such habitats.

    Among birds, insect-eaters like the wood warblers are migratory and leave after the breeding season. Seed-eaters (e.g., finches and sparrows) and omnivores (e.g., ravens) tend to be year-round residents. During poor cone years, normal residents like the evening grosbeak, pine siskin, and red crossbill leave the taiga in winter and may be seen at bird feeders here in Virginia.

    Distribution patterns within the boreal forest: The boreal forest is restricted to the northern hemisphere. It is circumpolar in distribution, as are many of the species which comprise it and even more of the genera. In general, plants have different species represented on North America and Eurasia; the mammals of both continents tend to be conspecific.

    There are latitudinal zones within the forest . Running north to south, one finds

    Alpine expressions of the biome: In Merriam's Life Zones, the Hudsonian and the Canadian zones correspond with the Boreal Forest

    In North America, several variants of the boreal forest occur in the mountains of the West.

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    Created by SLW, October 1996