Boreal Forest Ecosystems

The boreal forests ring the regions immediately south of the Arctic Circle in a vast expanse.The northern boreal ecoregion accounts for about one third of this planet's total forest area. This broad circumpolar band runs through most of Canada, Russia and Scandinavia. About two-thirds of the area is in Eurasia.

Known in Russia as the taiga, the boreal forest constitutes one of the largest biome in the world, covering some 12 million square kilometres. It has relatively few species, being composed mainly of spruces, firs, and conifers, with a smattering of deciduous trees, mostly along waterways.

Temperatures in the north forest can be lower than the Arctic tundra in winter. In central areas of Alaska and Siberia, far from the sea’s moderating influence, seasonal temperature fluctuations are the greatest on the planet. Central Siberia has the coldest temperatures outside of Antarctica, dropping as low as -68C (-90F), while in the summer it may reach +30C (+85F).

In this harsh winter climate, snow drifts may stay unmelted for more than six months. Water is locked up in snow and ice most of the year, so the vegetation has to cope with drought conditions. Average annual precipitation is only 38- 50 cm (15-20"), with much of that falling as snow. Temperatures are usually below freezing for six months of the year.

Although summers can be very warm, the growing season is a short 50-100 frost free days. There are only about 30 days when light is sufficient and the temperature high enough - 10C (50F) - for full size trees to grow.

Locked up in the boreal forests are vast amounts of carbon. Their biomass is so huge that during their maximum growth phase in the spring and summer, worldwide levels of carbon dioxide fall, and worldwide levels of oxygen rise. The boreal forests are just as important to the global ecosystems as the tropical rainforests, and should be given equal attention.

The taiga acts as a carbon sink, meaning it takes more carbon dioxide out of the atmosphere than it puts in. The forest is the world’s richest source of softwood timber and pulpwood for making paper, and it has been increasingly exploited over the last 200 years. In this cool climate, forest regeneration is painfully slow, and can take centuries. When trees are cut down the sun’s rays reach the surface providing growing conditions for smaller vegetation. Without the binding action of tree roots, soil erosion begins on deforested slopes.

The most characteristic feature of the boreal forest is muskeg. A muskeg bog is neither land nor water, but a mixture of the two, like a thin, crusty porridge. Sphagnum moss forms a spongy mat over standing water, and wherever you stand, you’re standing in water. A few hardy plants that can tolerate wet, highly acidic conditions grow in the muskeg, such as black spruce, willow shrubs, cranberries, pitcher plants and orchids.

Hordes of insects, and therefore the muskeg bring thousands of migrating song birds north each year to breed in the boreal forest. The boreal is also dotted with thousands of rivers, small lakes, marshes and potholes in depressions left by retreating glaciers, which provide food and shelter for ducks, geese, swans and other waterfowl.

Fire is crucial to a healthy boreal forest. It removes old, diseased trees along with the pests in their bark. Some tree species, such as aspen and jack pine, actually need fire to stimulate their reproductive cycle. The nutrient-rich ash left behind helps fuel plant growth, and the variety of plant communities that spring up after a fire sustain different varieties of wildlife. The elimination of natural forest fire cycles in national parks, combined with the warming global temperatures, have allowed insect pests such as the pine beetle to decimate thousands of hectares of the forest.

Compared to the southern forests, there is much less diversity of both plant and animal life in the taiga. This is due to the relative geological youth of the forest, plus the severity of the winters.

Animal Adaptations

Mammals in this climate have thick layers of fur, and the boreal has a wealth of fur-bearing animals such as lynx, sable, mink, marten and others. In addition to insulating coats of fur or feathers, many animals of the north forest are larger than their cousins to the south, an advantage when it comes to conserving heat. Moose are the biggest deer, wolverine are the largest member of the weasel family, and capercaille are the biggest grouse.

The major large herbivores are the deer, with more species found in the northern forests than any other world habitat zone. Deer have an unusual circulation system to allow life in the snow. Veins and arteries send blood from the heart throughout the body and legs keeping them warm, while a different set of veins return the cooled blood back to the heart.

Some animals remain active throughout the winter, burrowing beneath the snow for warmth during the cold nights. Small rodents have elaborate tunnel systems dug into the snow so they can forage without ever going to the surface. Others eat as much as they can in the autumn and build up large fat reserves. They spend the winter hibernating in dens; their body temperature falls to near freezing; their heart rate slows dramatically and they seem lifeless. Bears give birth and suckle their young during the depths of a northern winter.

There are cold-blooded reptiles and amphibians living in the boreal forest. In North America, red sided garter snakes are found as far north as the Northwest Territories. They spend the frigid winter months coiled together in dens, with up to 8,000 individuals overwintering together.

Wood frogs live further north than any other amphibian in North America. Known as a freeze-tolerant species, they can remain frozen at -3C (26F) for several weeks. Up to 65% of their body fluids freeze, and they are able to freeze and thaw repeatedly.

Plant Adaptations

The typical conical shape of the evergreens is an adaptation to the cold winters and short growing season. The spire shape promotes shedding of snow and prevents loss of branches; the narrow shape of the needles reduces surface area where water may be lost through transpiration; a waxy coating also helps protect them from drying winds. By not losing their foliage in the winter, evergreens can photosynthesize as soon as temperatures warm in the spring, rather than first having to grow leaves. The dark colour of the spruce and fir needles also helps them absorb maximum heat from the sun.

The low temperatures mean plant decomposition is slow. The highly lignified needles of the evergreens decompose slowly, creating a thick mat over the soil. Tannins and other acids from the needles cause the upper soil layers to become very acidic, limiting undergrowth vegetation. The cool temperatures and permanent shade from the evergreens keeps evaporation to a minimum. The soils under the conifers are often wet, and in some cases they are waterlogged nearly all year, which limits nutrient recycling.

Effects of Global Warming on the Boreal Forest

• Trees in the boreal forest are being affected by acid rain generated by the burning of fossil fuels in industrialized areas far south of the forest; acid rain weakens trees, allowing insects and other pests to attack more easily. It also dissolves metals previously locked in the soil which are toxic to tree roots 
• Large scale mining and oil exploration and their accompanying roads, towns and infrastructure have totally disfigured the natural environment in many places. 
• Ore smelting plants and pulp and paper mills have produced massive air pollution 
• Unregulated trapping of fur-bearing mammals, and poaching of large predators such as Siberian tigers, Amur leopards and bears is reducing populations of hunters at the top of the food chain 

See also

• Forest Ecosystems
• Tropical Forest Ecosystems
• Temperate Forest Ecosystems