A biome is a large community of plants and animals that occupies a distinct type of environment. This section reports on six biomes and a seventh category of particular importance to Canadian ecosystems – ice across biomes.
Forests cover 3.5 million km2 (60%) of Canada’s landscape. Of this, about 70% is boreal forest. The northern boreal forest has relatively little human imprint, but the southern boreal forest is fragmented by human disturbance. Only 0.01 to 0.02% of Canada’s forest is lost annually to other types of land cover. Although old forests have shifted to young forests in some areas, old forests still make up 40% of both Newfoundland and Labrador’s boreal forest and British Columbia’s coastal rainforest. Ecosystems near northern and mountain treelines are changing. For example, trees are expanding northward along the Labrador coast and tree growth and density are increasing near treelines in the Yukon and northern Quebec.
Grassland losses exceed those of other major biomes in North America. Most loss in Canada occurred before the 1930s as the result of conversion for cropland. Estimates of total loss prior to the 1990s include 97% of tallgrass/savannah in southern Ontario, 70% of prairie grasslands (by far the largest of Canada’s grasslands), and 19% of bunchgrass/sagebrush in British Columbia. Losses continue in some areas, particularly small, remnant patches. Grassland health has also suffered. Over the long term, changes in natural disturbance regimes due to factors like fire suppression and confined cattle grazing have had negative impacts on grasslands. Sound stewardship practices in some areas are helping to address the problem. Other stressors include invasive non–native species, forest encroachment, fragmentation, and intensification of agriculture.
Approximately 16% of Canada’s land area is covered by freshwater wetlands, making the country steward to about a quarter of the world’s remaining wetlands. Wetland conversion was rapid in southern Canada post–settlement, with an estimated 200,000 km2 lost prior to 1990. Despite significant efforts to conserve and restore wetlands in some areas, overall loss and degradation continue. Wetlands near urban areas are particularly threatened, with 80 to 98% of original wetlands converted to other uses in or near Canada’s large urban centres. Current threats include conversion to other land uses, water regulation, pollution, and invasive non–native species. Climate change poses a significant threat to wetlands. In the North, wetland changes due to permafrost thaw and greater evaporation during warmer summers are already apparent.
Annual low flows in natural streams decreased at many sites in southern Canada and increased at sites in the west and northwest. Annual peak flows decreased at many sites across Canada, but increased in the Atlantic Maritime. Other trends, such as changes in seasonal average flows, were also specific to regions and types of streams. Changes in stream flow affect aquatic life. For example, decreased low flows can cause problems for late–spawning fish and increase heat stress and predation for all fish. Trends in lakes include decreases in seasonal and year–to–year water–level fluctuations in some of the Great Lakes. In Lake Ontario, since 1960, water–level regulation has reduced plant diversity and altered habitat for animals living along the shoreline.
On the Atlantic coast, wetlands, dunes, and beaches are at risk from coastal development and increased erosion – and are known to be declining in some areas. The erosion results from several interacting factors: changes from development make the shoreline more vulnerable, and rising sea level combines with more intense storm surges. On the Pacific coast, development in the early 20th century resulted in loss of intertidal wetlands, mudflats, and estuarine habitat. Losses continue today, with increasing human populations. Eelgrass meadows are internationally recognized as productive, at–risk coastal ecosystems. There is evidence of recent rapid declines in eelgrass in areas of James Bay, the Atlantic Coast, and the Gulf of St. Lawrence.
Management efforts to reverse long–term fisheries declines have been largely unsuccessful, hampered by shifts in ocean regimes and loss of habitat for spawning and rearing fish. Food webs in waters off all three of Canada’s coasts are changing. The most dramatic example is the increase in invertebrates, such as shrimp, following the collapse of Atlantic ground fish. Ocean changes include shifts to warmer, less salty seawater over the past few decades, a result of natural climate oscillations and, possibly, climate change. Ocean acidification, caused by the oceans absorbing the increased atmospheric carbon dioxide, is already occurring in Canada’s oceans, with severe consequences for marine biodiversity predicted by the end of this century.
Ice is a defining feature of much of the Canadian landscape and many plants and animals are adapted to seasonally or permanently frozen environments. Loss of ice alters entire biomes – thawing permafrost is already changing frozen peatland ecosystems to wetlands in some areas. Over the long term, thawing permafrost will lead to shifts in plant and animal communities across the current permafrost zone. Sea ice has undergone the most dramatic, large–scale decline, especially in the last few years. There are direct impacts on species, including seals, polar bears, Arctic cod and Arctic foxes. Indirect effects include changes in coastal climate and impacts on Arctic food webs, including the range expansion of killer whales into ice–free areas.