Boreal forests and taiga

The boreal forest is the world's largest terrestrial biome, characterized by coniferous forests. It makes up 29 percent (about 20 million hectares) of the world's forest cover. It occurs in a broad band (50–70 degrees north latitudes) across northern North America, Europe, and Asia in regions with cool temperatures and adequate moisture. It forms a nearly unbroken belt of trees that circles the Earth. Fifty-eight percent of the Earth's boreal forest is in Russia, 24 percent in Canada, and 11 percent in the United States. Boreal forest is also known as taiga or northern coniferous forest. The term taiga is of Russian origin and means “marshy pine forest.” The term boreal forest is sometimes used to refer to the more southerly part of the biome, while the term taiga is often used to describe the more barren areas of the northernmost part.

The boreal forest has a subarctic climate characterized by long, cold winters and short, cool to mild summers. The main seasons in the forest are winter and summer. The spring and autumn are so short that we hardly know their existence. Long, cold winters last up to six months, and short summers last one to three months. There is a very large temperature range between seasons. Summer temperatures are mostly cool, averaging from about 19 degrees F to 70 degrees F (minus 7 degrees C to 21 degrees C), and winter temperatures range from about minus 65 degrees F to 30 degrees F (minus 54 degrees C to minus 1 degree C). Mean annual precipitation is relatively low (average 12–33 inches, or 300–850 millimeters), but low evaporation rates make the region a humid climate, which is sufficient to sustain the dense vegetation growth. The precipitation arrives mostly as rain in summer, but also as snow in winter. Annual snowfall varies from about 15 to 40 inches (40 to 100 centimeters). The average length of the growing season in boreal forests is about 130 days, and the length varies in different regions. For example, growing season varies from 80 to 150 days in the boreal plains in Canada, and from 100 to 140 days in the boreal shield.

As a result of its glacial history, most of the boreal forest's soil is geologically young and nutrient poor. Soil development progresses in the forest are very slow because of cold climates. Fallen leaves and moss can remain on the forest floor for a long time in the cool, moist climate, which limits their organic contribution to the soil; acids from evergreen needles further leach the soil. As a result, plants cannot efficiently use much of this mineral content in the soil. There are only lichens and mosses growing on the forest floor because of the acidic soil. In some parts of the forest, permafrost exists, which makes it difficult for plants to root deep into the soil generally.

Overlying formerly glaciated areas and areas of patchy permafrost, the forest is a mosaic of successional and subclimax plant communities that are sensitive to varying environmental conditions. The boreal is typically dominated by a few species of coniferous trees, such as spruce (genus Picea), fir (Abies), pine (Pinus), and larch (Larix). There are two main types of boreal forest. One is called “closed forest,” which has trees that grow close together and a shaded, often moss-covered forest floor. The other is called “open, lichen woodland,” which has trees spaced far apart, with lichen growing in open areas. Decomposition rates are relatively slow due to cool temperatures. Leaf litter in the boreal decomposes 60 times slower than that in the rainforest. Slow decomposition results in an accumulation of peat and humic acids, which render many soil nutrients unavailable for plant growth and limit diversity and productivity of the few tree species. Often the canopy is not dense, and a well-developed understory of acid-tolerant shrubs, mosses, and lichens may be present in the most mesic sites.

Compared with the tropical or temperate biomes, there are not a lot of plant species in the boreal because of the harsh conditions. Flora consist mostly of cold-tolerant evergreen conifers with needlelike leaves, such as pine, fir, spruce, and hemlock. In North America, one or two species of fir and one or two species of spruce are dominant. Across Scandinavia and western Russia, the Scots pine is a common component of the boreal, while the boreal of the Russian Far East and Mongolia is dominated by larch, a deciduous conifer species. It also has some broadleaf deciduous trees such as birch, aspen, and poplar, mostly in areas escaping the most extreme winter cold. Underneath the trees, some shrubs (e.g., blueberries, willows, and alders), herbs, mushrooms, lichens, and mosses grow.

The Boreal Habitat

The boreal forest provides habitat for diverse wildlife, including a large range of birds, mammals, and insects. Fauna include woodpeckers, hawks, moose, bear, weasel, lynx, fox, wolf, deer, hares, chipmunks, shrews, and bats. Over 300 bird species live in the boreal in the summertime, while only 30 species stay for the winter. The rest are summer visitors, and they migrate there to nest and feed because the boreal has millions of insects in summer, providing abundant food for birds. The forest also provides birds with a good place to raise their young, with generally more space and less competition with other birds than in the tropic and temperate forests. In fact, about 30 percent of North American migratory birds depend on the boreal for breeding habitat. The boreal is also rich with large herbivorous mammals (e.g., moose and caribou), carnivorous (e.g., lynx, coyote, foxes, and weasels), and omnivores (e.g., bears and raccoons). Although the boreal does not have as many animal species as the tropical or the temperate biomes, it does have millions of insects in the summertime.

For example, Canada's boreal forest includes an estimated 32,000 species of insects. These insects play an important role in the forest—they decompose litter, supply food for birds and small animals, and eliminate diseased trees. Unfortunately, a number of wildlife species are threatened or endangered with extinction in the boreal, including the Amur (Siberian) tiger, the Amur leopard, woodland caribou, American black bear, grizzly bear, and wolverine. For example, the Amur tiger, the largest of all cats, has all but disappeared from China, Korea, and most of Siberia, and a small population (less than 400 lives) in the far east of Russia. Habitat loss, fragmentation, and extensive poaching for illegal trade are the primary cause of decline of these species.

Mainly covered with forest, the boreal zone also contains a large amount of lakes, rivers, wetlands, bogs, and fens that support beaver, fish, waterbirds, and many other wildlife. Especially in Canada, the boreal contains 25 percent of the world's wetlands, extending over more than 459,460 square miles (1.19 million square kilometers). It has been estimated that Canada's boreal region contains over 1.5 million lakes with a minimum surface area of almost 10 acres (40,000 square meters).

The extensive undammed watered landscape of the boreal serves as last refuge for many of the world's sea-run migratory fish, including half of the remaining populations of North American Atlantic salmon. The watered landscape also makes vast and critical contributions to the global environment by stabilizing climate and feeding the productivity of the world's oceans. The wetlands and peatlands store an estimated 147 billion tonnes of carbon, more than 25 years worth of current man-made emissions. The input of freshwater from boreal rivers to the Arctic and other northern seas is critical to forming sea ice, which cools the atmosphere and provides the basis for much of arctic marine biodiversity.

A Threatened Treasure

Around the world, boreal forests are highly valued by humans. They supply many ecosystem goods and services. They act as a reservoir for maintaining biological and genetic diversity. Boreal forests store carbon, purify air and water, and help regulate regional and global climates. They also provide food, renewable raw materials, and outdoor recreational places for human use. In Canada alone, the boreal have long been central to the natural environment, history, culture, and economy of the country. More than 4 million people live in Canada's boreal, and the boreal sustains over 7,000 forestry businesses and 400,000 jobs. For Canada's aboriginal people, the boreal sustains the traditional lifestyle and provides many plant resources that hold special dietary, medical, economic, and spiritual value.

Boreal forest has been influenced and shaped by natural disturbances such as wildfires and insect infestations, which create openings or clearings in the forest. The forest provides a large amount of fuel for fires. Conifer needles and branches are highly flammable, especially during dry weather. The number and distribution of forest fires and area burned varies annually across the boreal. In Canada, there are about 8,000 forest fires recorded every year, which burn, on average, about 2.1 million hectares of the forest annually. That average annual burn area is equivalent to more than three times the current annual industrial timber harvest. Fire is a recurring event in the boreal. The recurrent cycle of large, damaging fire occurs approximately every 70 to 100 years. Fire is a natural and essential part of the boreal forest ecosystem, and many boreal plants and animals flourish in the aftermath of wildfires. For example, the intense heat of the fire releases seeds from hardy cones of black spruce, jack pine, and lodgepole pine. Moose invade the burned area after a fire to find food (various parts of deciduous trees and shrubs). Insects are big consumers of trees. Repeated attacks by insects can kill a tree or weaken it. Acres of trees may be partly defoliated in a single season by insects such as the spruce budwork or the larch sawfly.

Despite its global significance, the boreal forest is in great danger today. Industrial logging, mining, hydroelectric dams, and global warming are among the largest threats to the boreal forest. The boreal forest is being clear-cut to create building materials and consumer products such as toilet paper, office paper, books, and catalogs. Approximately half of the boreal forest is under lease to forestry companies. In Canada, it was estimated that the annual harvest in the boreal was about 1 million acres (404,686 hectares) per year. In addition to unsustainable logging, exploration and development of oil and natural gas reserves is another large threat to the boreal. From Alaska to Canada to Russia, it is estimated that vast amounts of petroleum products lie under these forests. The high demand for fossil fuels nowadays is pushing exploration and development in the boreal. Global warming is another serious threat. The boreal biome is expected to experience the greatest increase in temperature as a consequence of global warming, especially during the last three decades. Therefore, the boreal forests should suffer most from the climate change. Scientists have already noted that the impacts of climate change on the forest are expected to be largely detrimental. The warmer and drier weather in the summer is also expected to increase tree mortality and reduce tree growth and reproduction. The effects of climate change are expected to create unprecedented levels of insect infestation, drought, and forest fires in the boreal forest.