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The Northern Boreal Forest, sometimes also called Taiga or Northern Coniferous Forest, stretches unbroken from eastern Canada westward throughout the majority of Canada to the central region of Alaska. The Northern Boreal Forest biome also covers extensive areas of Asia and Europe. Taken together the Northern Boreal Forest of North America and Eurasia consitutes Earth's most extensive biome. The Northern Boreal Forest of North America is dominated by a few species of conifers. In contrast to the richness of the forests of the Eastern Deciduous Forest, the dominant tree species of the Northern Boreal Forest can be counted on the fingers of one hand; Black Spruce, White Spruce, Balsam Fir, Paper Birch, and Quaking Aspen. There are other species, of course, but the relative diversity of tree species is very low compared to the Eastern Deciduous Forest.

In eastern North America the Taiga is bounded on the south by a transition zone between it and the northern reaches of the Eastern Deciduous Forest. The midwestern region boundary is with the Prairie Biome and the transition is marked by a scrubby forest of Quaking Aspen, Paper Birch, small conifer individuals intermixed with patches of Prairie. The southwestern boundary of the Northern Boreal Forest is with the Montane Coniferous Forests of British Columbia and Alberta. To the north, of course, is the tundra.

The Northern Boreal Forest covers a wide variety of climatic differences, but all climates in the Northern Boreal Forest tend to have cold, long winters, short cool summers, and low precipitation. The two graphs on the left show average annual temperature and precipitation for localities at the two margins of the Northern Boreal Forest. Fort Yukon is located in east-central Alaska and is on the boundary between the Northern Boreal Forest and the tundra. Iron Mountain, Michigan is located in the transitional zone between the Northern Boreal Forest and the Eastern Deciduous Forest.

Fort Yukon is obviously a very cold and dry place. Iron Mountain is considerably wetter and warmer, but its annual precipitation is still less than that typical of the Eastern Deciduous Forest. The tundra to the north is even colder and drier than the climate at Fort Yukon. Indeed precipitation levels in the northern half of the Northern Boreal Forest and the Tundra are equivalent to those of the deserts of the United States and northern Mexico.
The Northern Boreal Forest, in short, is dry and cool. Why should there be so little precipitation? Cool air holds less water than warm air and, consequently there is less water to form precipitation. Moist, warm air from the Gulf of Mexico rarely reaches this far north and moisture laden air from the Pacific dumps most of its water along the Pacific Coast because of the mountain ranges in the region and the rapidly cooling temperatures as one moves inland.

The description of the Northern Boreal Forest as a place of little precipitation poses a contradiction, however. As you walk through the Northern Boreal Forest you see water everywhere; swamps, marshes, bogs, rivers, and lakes. If the Northern Boreal Forest is really that dry, where does all the water come from? There is no single answer, but a number of factors figure into the equation.

1. The Northern Boreal Forest is located in an area of flat topography and water does not run off readily.

 

2. Water evaporates more rapidly in warm area than in cool air. Therefore the cooler the climate, the slower the rate of evaporation.

3. Sphagnum Moss (picture above). Sphagnum moss is an atypical genus of mosses found throughout the boreal regions of both the northern and southern hemispheres. As you look at the Northern Boreal Forest you may think that the Wolf, Black Spruce, or the Snowshoe Hare are the dominant component of the ecosystem. Not so. The king of Northern Boreal Forest is the lowly Sphagnum Moss. Sphagnum Moss grows in wet environments. Bogs are covered with Sphagnum moss and you see it everywhere while walking in the forest. The northern half of the Northern Boreal Forest is dominanted by a type of ecosystem called Muskeg. Muskeg is literally a solid mat of Sphagnum Moss with a few spindly Black Spruce. Sphagnum Moss contains specialized cells that store water and the mass of moss acts as a great sponge holding water. Sphagnum Moss covers over small bodies of water (bogs) and prevents evaporation. Dead sphagnum moss under the cool, acid conditions of the Northern Boreal Forest does not decay but forms a layer of Peat. Peat and disolved salts form a hardpan preventing water from draining into the underground rock strata (aquifers).

4. Most of the soil of the northern half of the Northern Boreal Forest and the Tundra is permanently frozen all year, the so-called Permafrost. The upper soil layer thaws during the summer (Active Layer), but a layer of ice is always present below the active layer preventing water from draining into the underground rock strata.

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