The greatest threat to the boreal forest is deforestation. There is an increase in industrial logging operations which clearcut large areas of boreal forest across North America, Scandinavia and Russia for timber and pulp. Deforestation is happening faster in boreal forests than rainforests. Even though some forests are replanted, there is a growing trend in North America, Scandinavia and Russia to fell mixed conifer forest and replant with single species: Pinus contorta, Pinus sylvestris and Picea abies being common choices.
Road construction for industrial and military purposes is destroying wilderness areas.
'Acid rain' or acidification is a major cause of forest deterioration. Coniferous forests seem especially vulnerable to such pollution. Rising levels of Carbon dioxide may alter climate in the high latitudes enough to affect presently grown conifer species, some of which require a cold winter to flourish. Over half of the existing boreal forest may disappear, due to the effects of climate change.
Fire is the major natural disturbance agent in the boreal forest. Large scale insect outbreaks can weaken or kill trees over vast areas, often leading to forest fires. Where human settlements and transportation routes are present in the boreal forest the great majority of the number of individual fires are human caused. However, around 90% of the area burned in the North American boreal forest is the result of natural ignition caused by lightning. Observations from satellites indicate that during the 1987 fire season approximately 14.5 million ha were burned in Asia.
The taiga or boreal forest exists as a nearly continuous belt of coniferous trees across North America and Eurasia in a circumpolar belt of the far northern hemisphere immediately south of the Arctic Circle. Within this boreal zone, forests and other wooded land cover 1.2 billion hectares (ha) of which 920 million ha are closed forest. The latter number corresponds to about 29% of the world's total forest area and to 73% of its coniferous forest area. The boreal forest region is variously reported as occupying between 11 to 17 percent of the earth's land surface area and is equivalent to about 18 percent of the earth's total biomass. The biomass is so huge and so vital that when the taiga is in maximum growth phase during the northern spring and summer, the worldwide levels of carbon dioxide fall and the worldwide levels of oxygen rise.
Extensive parts of the boreal forest occur on permafrost soils and formerly glaciated areas. and corresponds with regions of subarctic and cold continental climate. Primary productivity is often limited by cold soil temperatures. Long, severe winters and short summers are characteristic, as is a wide range of temperatures between the lows of winter and highs of summer. Mean annual precipitation is 15 to 20 inches, but low evaporation rates make this a humid climate.
Of all the major forest regions of the world, the boreal zone supports the lowest density of settled human populations.
Needleleaf coniferous trees are the dominant plants of the taiga biome. A very few species in four main genera are found: the evergreen spruce Picea sp., fir Abies sp. and pine Pinus sp., and the deciduous larch or tamarack Larix sp. In North America, one or two species of fir and one or two species of spruce are dominant. Across Scandinavia 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 sp., birch Betula sp., and aspen Populus sp. So-called climax communities in the taiga undergo an approximately 200-year cycle between nitrogen-depleting spruce-fir forests and nitrogen-accumulating aspen forests.
A distinctive feature of the flora of boreal forest is the abundance and diversity of mosses. An estimated one third of the ground cover under boreal forest as a whole is dominated by moss. It is probable that in no other major ecosystem region of the earth are mosses more prominent. Moss makes up much of the ground cover in older conifer stands, and grow on rocks, tree boles, and in the pits formed by upturned trees. Extensive peaty wetlands in the boreal region are often thick accumulations of dead sphagnum, other mosses, sedges, and other plants; a living moss layer continually grows at the surface. Lichens make up a significant part of ground cover in the lichen woodland or sparse northern taiga. Lichens are also generally well distributed on tree boles and especially in the canopy of older conifers throughout the boreal forest. Much of the boreal forest still supports most of its native wildlife including free-ranging large predators such as wolves, lynx and bear; also various members of the weasel family (e.g. wolverine, fisher, pine martin, mink, ermine and sable). 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).