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 150200 or more years of age.
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.
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.
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.
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
Department of the Environment. State of the Environment Report, Terrestrial Ecosystems. Edmonton: n.p., 2001. With permission from Alberta Environment.