The world's largest land biome is only about 12,000 years old
The taiga, or boreal forest, blankets 17 million square kilometres across Canada, Alaska, Scandinavia and Siberia, more than a tenth of Earth's land. Yet in its present form it appeared only after the last ice age, spreading over ground that had been ice sheet or mammoth steppe. Its winters can outdo the tundra's for cold.
The name comes from Russian tayga, probably from Turkic or Mongolic words for wild, wooded country. North American writers sometimes reserve taiga for the sparse northern fringe near the tundra and call the whole belt boreal forest, while Russian usage applies taiga to the entire biome. Conifers dominate: spruce in North America, spruce mixed with pine and birch in Scandinavia and Finland, and in eastern Siberia a vast forest of larch. Only deserts and xeric shrublands cover more land, and Russia and Canada hold the largest share.
Apart from ice caps and tundra, no land biome averages colder, with mean annual temperatures of roughly minus 5 to plus 5 °C. Parts of eastern Siberia and interior Alaska and Yukon average minus 10 °C, and the lowest reliable temperatures in the Northern Hemisphere were measured in the taiga of northeastern Russia. A typical winter day might be minus 20 °C and a summer day 18 °C, but summer lasts only one to three months against five to seven months of freezing winter. The Dahurian larch of eastern Siberia survives the harshest cold of all.
Plants cope by starting growth at lower temperatures than most, and some sources cite a growing season of about 130 days. That shrinks to 50 to 70 days at the edge where forest yields to tundra, and stretches to 145 to 180 days on oceanic coasts of Scandinavia and Finland. Precipitation is modest, usually 200 to 750 millimetres a year, but evaporation is so low that water still outpaces loss, supporting big trees where a warmer steppe with similar rain would hold mostly grass. Near the Arctic Circle, summer brings midnight sun and winter polar night.
Soils are young and poor. Recently retreated glaciers left hollows that filled into lakes and muskeg bogs, and acidic needles leach the ground into podzol, where often only lichens and mosses grow. Even so, the variety of soil organisms rivals that of tropical rainforest. Because the Bering land bridge once joined Asia and North America, many animals and some plants occur right around the pole. Climate change threatens the biome, and how to count the carbon it absorbs or releases remains disputed.
Source: Taiga
