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Old-Growth Forests

Old Growth ForestThe term Old-Growth Forests describes ecological conditions where large trees in the mature stages of their life cycle generally dominate the forest vegetation. The old-growth stage may be reached at different ages depending on the tree species and site condition. At 50 to 100 years old, aspen forests can be dominated by large trees nearing the end of their life cycle. In undisturbed coniferous forests, spruce trees can reach 150–200 or more years of age.

Old-Growth forests have a more complex structure than younger stands. This is due largely to the presence of fallen trees, snags, gaps in the canopy, shrubs and understory vegetation. This structural diversity provides a greater variety of micro-habitats. Consequently, there is a particularly rich diversity of mosses, lichens, insects, and smaller microbial organisms. Many forest species require old-growth stands for part of their life cycle. Examples in Alberta include woodland caribou, fisher, flying squirrel, bats, forest owls and hawks, and a variety of songbirds.

Certain old-growth forests in Canada, with trees hundreds of years old, have become the focus of major disputes regarding appropriate use. Among the most contentious issues are logging versus conservation of the old-growth temperate rain forests of British Columbia, the eastern white pine and red pine forests of Ontario, and the hardwoods of the Maritimes. Public interest in their conservation centres on old-growth forest ecosystems, with their many unrecorded species and general vulnerability to change. There are also many strong aesthetic, recreational and spiritual values associated with these ecosystems.

Alberta's forests have developed under a history of frequent fire. As a result there are few areas where forests are over 200 years old. Stands of older trees tend to be found in river valley floodplains and areas with a higher moisture regime. Even where older forests are found, light fires may have passed through these stands, burning the understory vegetation.

Over the past century, fire suppression has changed forests in Alberta and other parts of North America, allowing more stands to reach maturity. This also increases the quantity of fuel (deadwood) available to be burned and consequently, it has increased the risk of major, intense forest fires.

Prescribed burning and timber harvesting can be used to reduce the risk of catastrophic fires. The goal is to incorporate natural disturbance patterns into forest management planning at the landscape level to break-up the large, even-aged stands produced after major fires, and reduce the overall fuel load. The resulting forest will feature a variety of forest stages, including areas of old-growth forest.

Department of the Environment. State of the Environment Report, Terrestrial Ecosystems. Edmonton: n.p., 2001. With permission from Alberta Environment.



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