|Nature Gallery (Eco Regions)|
Boreal Evergreen Forests
|A great band of evergreen conifer forests extends around the northern hemisphere in the subarctic latitudes. Within this zone, the growing season is brief and the winter is long and cold. These circumstances exclude most broadleaf deciduous trees, which require more time to regrow their leaves than the subarctic climate provides. Evergreen trees, on the other hand, are ready to resume photosynthesis whenever the air grows mild enough. Furthermore, the compact, cylindrical shape and waxy skin of the needle-like leaves retard moisture loss during the winter, when environmental water is unavailable because it is frozen.|
|Compared with the forests
of lower latitudes, the boreal
forests—often called by their Russian name of taiga—are
rather uniform in structure and species
composition. Trees, often in dense stands of even age, dominate. Many
assume a narrow, pointed habit that permits snow to be shed readily.
within the shady forest is sparse, comprising low shrubs, many of them in
family, and a layer of mosses. Another conspicuous feature of the taiga
region, from which the ice
sheets retreated only about 10,000 years ago, is the countless ponds
that pock the flat and poorly drained terrain.
In Eurasia, the taiga spans the continent from the Russian Far East to Scandinavia. The westernmost forests are very monotonous, but the number of species increases as one moves to the east, and the forests of Hokkaido in northern Japan are comparatively diverse. An exception to the evergreen character of most of the taiga is the deciduous larch forests of eastern Siberia, where the bitterly cold winters of the continental interior make the retention of any leaves, even needles, a liability.
The boreal forests of North America are richer in species than their Eurasian counterparts but are in other ways similar. The north–south alignment of North American mountain ranges means that taiga-like conifer forests extend far into the temperate zone along the spines of the Cascade Range and Sierra Nevada, the Rocky Mountains, and the Appalachians.