Taiga

I

Introduction

Taiga or Boreal Forest (also Northern Coniferous Forest), forest biome covering about 11 per cent of the Earth's land surface, or one third of its total forested area (about 1.5 billion hectares/3.7 billion acres). It occurs in the Northern hemisphere, in a circumpolar band, running though Canada, Scandinavia, Russia, China, Mongolia, the Korea Peninsula, and northern Japan. Although taiga is the Russian name, it can be used interchangeably with “boreal forest” for the biome as a whole. In addition to these forests in high latitudes, pockets of the biome can also be found at high altitude in more southerly mountainous regions. These are known as oroboreal forests, from the Greek word oro meaning “mountain”.

The region is of great importance because of its size and biodiversity. These areas constitute some of the largest extent of wilderness on the planet. The impact of human activity and habitat loss in such areas is, however, becoming a matter of concern.

II

Climate

Climate controls the distribution of the high latitude boreal forests. They occur in regions with subarctic and cold continental climate characterized by long severe winters (up to six months with mean temperatures below freezing) and short warm summers (50 to 100 frost-free days). Average winter temperatures are as low as -30^o C(-22° F), while summers are cool averaging 6 to 14^o C (43 to 57° F). Due to the size of the land areas, there is often little moderating influence from the sea, and temperatures can be extreme. Precipitation is also low, ranging from 350 mm to 500 mm (14 in to 20 in). The strong winds cause high evaporation rates and the wind chill factor is high. Due to the high latitude, the daylight period is short in winter and long in summer. To the north, the forest grades into the tundra biome, where temperatures are too low to support full-sized tree growth. In the south the taiga gives way to grasslands in the drier continental interiors or deciduous forest in the more moist, maritime climates.

III

The Taiga Ecosystem

A

Plants

The forests are dominated by gymnosperms. These are cone-bearing tree species, and those found in the taiga have needle-shaped leaves. The most common species are members of the spruce (Picea), fir (Abies), and pine (Pinus) families, along with deciduous trees such as larch (Larix). In North America, black and white spruce are found as well as jack pine and balsam fir. In Scandinavia and western Russia the Scots pine (Pinus sylvestris) is common.

Conifers are adapted to the cold and the drought conditions of winter when water is frozen. Their conical shape allows snow to fall off easily, while the small surface area of their needles reduces water loss through transpiration, and a thick, waxy cuticle protects the leaf stomata from the drying winds and prevents water loss. By retaining their dark-coloured leaves throughout the year (see Evergreen), the trees are ready to photosynthesize as soon as temperatures rise above 6° C (43° F) in spring. The evergreen strategy enables them to exploit fully the short growing season.

The coniferous forest is the climatic climax vegetation. However, variations in topography, soils, and local climate result in a mosaic of different types of forest. Patches of broadleaf temperate forest occur in sheltered areas and to the south of the region. Species from the birch (Betula), aspen (Populus), and alder (Alnus) families are common. Where drainage is poor and the terrain low-lying, extensive bog areas with lakes and swamps are found with associated peat soils. Forests dominated by larch cover large tracts in Eurasia where they are underlain by permafrost. The winter drought here occurs for such long periods that conditions are too harsh to support the other boreal species. These different types of mosaic are very important because they increase the biodiversity of the taiga.

B

Animals

The taiga supports a variety of animals. The major herbivores are deer, with more species found here than in any other biome. Small herbivores include rodents such as beavers and voles. Predators include members of the weasel family, as well as lynxes and wolves.

Many animals show specific adaptations to the conditions found in the biome. For example, many have thick coats of fur or feathers for insulation. Large body size, relative to similar species found in more southern biomes, is another strategy that prevents heat loss. For example, the elk is the largest member of the deer family, and the wolverine is the largest of the weasels. Several species, such as the northern red-backed vole, shrews, and lemmings, have developed the ability to live beneath the snow-covered ground in winter. Others (such as the brown bear, Siberian chipmunk, and squirrel species) over-winter by hibernation. Some animals do not hibernate, but hoard or store food to enable them to survive the winter period.

Migratory behaviour is also a common adaptation to the climate of the taiga. In North America, for example, Barren Ground caribou migrate south into the biome from the tundra in winter. By contrast other birds and mammals only spend the summer months in the taiga, moving further south when temperatures fall.