Forest Structure and Species

Because many hardwood trees are both sensitive to low winter temperatures and require a long and warm summer, the true boreal forest begins where the few remaining hardwoods become a minor part of the forest. Four coniferous genera dominate a major part of the taiga: Picea (spruce), Abies (fir), Pinus (pine), and Larix (larch). The hardwoods, which largely occur in dwarf form, include Alnus (alders), Populus (poplars), Betula (birches), and Salix (willows). The hardwoods tend to be early successional species following disturbances such as fires or erosion/deposition processes on riverbanks, which are eventually shaded out by slower-growing spruces and firs. Much of the main boreal forest is dominated by a few spruce species. These form a dense canopy in the central and southern taiga, with a ground cover of dwarf shrubs, such as cranberries and bilberries, and mosses and lichens. In northern Siberia, huge areas are covered almost solely by larch, and the canopy is much less dense. Pine species, which can withstand a range of harsh conditions, grow in light, sandy soils and other dry areas. As the boreal forest-tundra boundary is approached, conifers thin out to a woodland, with lichen and moss dominating the ground. Trees become more and more stunted.

The standing stock of biomass of the boreal forest ranges is estimated at 200 (range 60-400) metric tons per hectare (t ha— ). This compares with an estimate of 350tha—1 for the temperate deciduous forest and 10tha—1 for the tundra ecosystems. The boreal forest differs from the temperate forest in having a much higher percentage of its total biomass as photosynthetic foliage (7% vs. 1%). It differs from the tundra in having a lower percentage of root biomass (22% vs. 75%).

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