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The Canadian boreal forest is a very large bio-region that extends in length from the Yukon-Alaska border right across the country to Newfoundland and Labrador. It is over 1,000 kilometres in width (north to south) separating the arctic tundra region from the various landscapes of southern Canada. The taiga growth (as defined in North America) along the northern flank of the boreal forest creates a transition to the tundra region at the northern tree line. On the southwestern flank, the boreal forest extends into sub-alpine and lower elevation areas of northern British Columbia. The central interior of the province is occupied by a sub-boreal transition zone between the main boreal forest and the dry forests of the southern interior. However, across the Prairie Provinces, a band of aspen parkland marks a different kind of transition along the south-central flank from boreal forest to grassland. In Central Canada, the southeastern flank is marked by the Eastern forest-boreal transition of Central Ontario and western Quebec. It consists mainly of mixed coniferous and broad-leaf woodlands. South of this transition can be found the deciduous woodlands of Southern Ontario.

Canada’s boreal forest is considered to be the largest intact forest on earth, with around three million square kilometres still undisturbed by roads, cities and industrial development.Its high level of intactness has made the forest a particular focus of environmentalists and conservation scientists who view the untouched regions of the forest as an opportunity for large-scale conservation that would otherwise be impractical in other parts of the world.

General forest ecology

The Canadian boreal forest in its current form began to emerge with the end of the last Ice Age. With the retreat of the Wisconsin Ice Sheet 10,000 years ago, spruce and northern pine migrated northward and were followed thousands of years later by fir and birch.About 5,000 years ago, the Canadian boreal began to resemble what it is today in terms of species composition and biodiversity. This type of coniferous forest vegetation is spread across the Northern Hemisphere. These forests contain three structural types: forest tundra in the north, open lichen woodland further south, and closed forest in more southern areas. White spruce, black spruce and tamarack are most prevalent in the four northern eco-zones of the Taiga and Hudson Plains, while spruce, balsam fir, jack pine, white birch and trembling aspen are most common in the lower boreal regions. Large populations of trembling aspen and willow are found in the southernmost parts of the Boreal Plains.

One dominant characteristic of the boreal is that much of it consists of large, even-aged stands, a uniformity that owes to a cycle of natural disturbances like forest fires, or outbreaks of pine beetle or spruce budworm that kill large tracts of forest with cyclical regularity. For example, the many stands of white spruce, black spruce, and balsam fir are vulnerable to the cyclical outbreaks of a species of the spruce budworm, the Choristoneura fumiferana. Since the melting of the great ice sheet, the boreal forest has been through many cycles of natural death through fire, insect outbreaks and disease, followed by regeneration. Prior to European colonization of Canada and the application of modern firefighting equipment and techniques, the natural burn/regeneration cycle was less than 75 to 100 years, and it still is in many areas.

Terms like old growth and ancient forest have a different connotation in the boreal context than they do when used to describe mature coastal rain forests with longer-lived species and different natural disturbance cycles. However, the effects of forest fires and insect outbreaks differ from the effects of logging, so they should not be treated as equivalent in their ecological consequences. Logging, for example, requires road networks with their negative impacts, and it removes nutrients from the site, which may deplete nutrients for the next cycle of forest growth. Fire, on the other hand, recycles nutrients on location (except for some nitrogen), it removes accumulated organic matter and it stimulates reproduction of fire-dependent species.

Ecosystems

Typical upland taiga in Quebec

Canada’s boreal region can be divided into seven ecozones. These seven can be divided into two main groups. The northern regions of the boreal forest consists of four eco-zones – Taiga Cordillera, Taiga Plains, Taiga Shield and Hudson Plains – that are the most thinly treed areas where the growing season and average tree size progressively shrinks until the edge of the Arctic tundra is reached.The southern tier of the boreal meanwhile consists of three other ecozones that form the largely uninterrupted or continuous forest in stretching as far south as Lake Superior in Ontario (as the Central Canadian Shield forests ecoregion) and the Manitoba-North Dakota border. These three southern zones are the Boreal Shield, at 1,630,000 square kilometres the largest of the eight zones, the Boreal Plains and Boreal Cordillera. A typical ecoregion of this southern tier would be the Eastern Canadian Shield taiga that covers northern Quebec and most of Labrador. Within the boreal region, there are about 1,890,000 square kilometres that are between 80% to 100% forested and another 650,000 square kilometres with 60% to 80% forest cover.

Forest species

The Calypso orchid grows in the shade of boreal forest.

Most trees native to the Canadian boreal are conifers, with needle leaves and cones. These include: black spruce, white spruce, balsam fir, larch (tamarack), lodgepole pine, and jack pine. A few are broad-leaved species: trembling and large-toothed aspen, cottonwood and white birch, and balsam poplar. There are large areas of black spruce, a species which is tolerant of shallow soil, permafrost, and waterlogged substrates, although as a consequence they have relatively low biological productivity. Owing to the short growing season, generally infertile soils, generally shallow soils, and frequent waterlogging, most of these forest types are slow-growing species, which generally tend to predominate in stressed habitats. Similarly, many of the understory shrubs are in the Ericaceae, a family known to tolerate acid, infertile and flooded habitats: examples include Labrador tea, sheep-laurel and blueberry. Since nutrient levels are so low, overall, the productivity of forest trees is highly dependent on the rate at which mineral elements such as nitrogen and phosphorus are recycled by litterfall and decomposition. After logging, the loss of nutrients may convert forested areas into shrub barrens dominated by shrubs such as sheep-laurel.Many of the plant species are fire-dependent, since fire removes neighbouring plants, and recycles nutrients locked in organic matter.

Although there are rather few species of trees in the boreal forest, there is a considerable diversity of other kinds of plants. An accurate summary is difficult, since most compendia on plants are organized by political, rather than ecological boundaries; one exception addresses the flora of the Hudson Bay Lowland,but much of this area is not forested. One portion of the boreal forest can be used to illustrate plant diversity; consider the Flora of the Yukon.In this western part of the boreal forest, there are, for example 127 species of grass (Poaceae), 118 species of Asteraceae, 115 species of sedge (Cyperaceae), 93 species of crucifer (Brassicaceae), 52 species of Rosaceae, 37 species of Saxifragaceae and 36 members of the snapdragon family (Scrophulariaceae). Overall, the flora has 1112 species – there are even 15 species of orchids.

A Sphagnum bog with spruce trees on a forested ridge in Quebec

Inland water and wetlands

Canada’s boreal landscape contains more lakes and rivers than any comparably sized landmass on earth. It has been estimated that the boreal region contains over 1.5 million lakes with a minimum surface area of 40,000 square metres as well as some of Canada’s largest lakes. Soft water lakes predominate in central and eastern Canada and hard water lakes predominate in Western Canada. Most large boreal lakes have cold water species of fish like trout and whitefish, while in warmer waters, species may include northern pike, walleye and smallmouth bass.

The boreal forest also has vast areas of wetland, particularly bogs and fens.Two wetland areas, the Hudson Bay Lowland and the Mackenzie River basin, are among the ten largest wetlands in the world.The boreal forest wetlands provide wildlife habitat (particularly for migratory birds), they maintain water flow in rivers, and they store significant amounts of carbon that otherwise would be released to the atmosphere.

Deforestation

Sheep laurel grows in clearings and shallow soils. It can form extensive shrub barrens after logging.

In contemporary times, the boreal forest has suffered little deforestation, defined as the permanent conversion of forest area to non-forest due to activities associated with agriculture, urban or recreational development, oil and gas development, and flooding for hydroelectric projects. In Alberta, the province with the largest oil and gas industry, more trees are cut for agriculture or oil and gas exploration than for timber.In eastern Canada, over 9,000 square kilometres of peatlands and forest have been flooded over the past four decades for hydroelectric projects. As of 2005, Canada as a whole has 91% of the forest cover that existed at the dawn of European settlement. More deforestation has occurred outside the boreal region, in more southerly areas of the country. The forest sector annually harvests approximately ½ of 1% of the region. However, this is not considered deforestation by some, given that provincial laws are meant to ensure that areas harvested by the forest sector are replanted or regenerated naturally. However, the resulting road network from logging has effects that persist long beyond the period of harvest; indeed, one can make the case that road construction is one of the most harmful and persistent effects of logging.

The Canada warbler nests on the ground in boreal forests.

Wildlife

There may be as many as five billion landbirds, including resident and migratory species. The Canadian boreal region contains the largest area of wetlands of any ecosystem of the world, serving as breeding ground for over 12 million waterbirds and millions of land birds, the latter including species as diverse as vultures, hawks, grouse, owls, hummingbirds, kingfishers, woodpeckers and passerines (or perching birds, often referred to as songbirds). It is estimated that the avian population of the boreal represents 60% of the landbirds in all of Canada and almost 30% of all landbirds in the United States and Canada combined.

Many of the wildlife species, are, like the forests, dependent upon natural disturbance from fire and insect outbreaks. For example, at least three species of warbler (Cape May warbler, bay-breasted warbler and Tennessee warbler), have distributions and abundance related to spruce budworm outbreaks. The black-backed woodpecker shows a preference for burnt over forests, where it forages for insects burrowing in the dead trees that remain standing. Fireweed, as the name suggests, is a plant that similar thrives in recently burned areas. Blueberries and huckleberries are also stimulated by fires, probably benefiting from the removal of shade, and the nutrients released in ashes. The resulting berries are an important food source for boreal forest animals.

Few species of boreal wildlife are classified under government conservation regimes as being at risk of extinction. However, the decline of some major species of wildlife is a concern. Boreal woodland caribou, whose lichen-rich, mature forest habitat spans the boreal forest from the Northwest Territories to Labrador, is designated as a threatened by the Committee on the Status of Endangered Wildlife in Canada. The Newfoundland population of marten is threatened by habitat loss, accidental trapping and prey availability.