18. Biodiversity of Canadian Forests
365
Obviously, the impact of clearcutting is not a simple reduction in
species diversity, but rather a differential effect , with some old-growth
dependent species of plants and animals being lost from the system,
presumably until suitable environmental conditions are restored. However, the scale and pattern of clearcuts are also vitally important in
determining the response of different species to disturbance. The resultant
spatial heterogeneity and fragmentation of the landscape have significant
impact of species diversity and abundance. Fragments smaller than a
species' home range will result in a reduction in abundance of that
species, or its complete elimination. The ecosystem itself may then be
threatened with destruction. Research on boreal fragmentation in Sweden
has demonstrated that 1 ha reserves that are required by law are composed
entirely of edge habitat, and therefore do not function as forest ecosystems
(Dr. Per-Anders Esseen, personal communication). Because edge effects
penetrate some distance into the remaining forest, even a low intensity of
clearcutting can cause substantial habitat fragmentation (Hansen, Spies,
Swanson et aI., 1991). Pielou (1990) has also called attention to the
potential loss of genetically distinct demes , and the consequent impact on
genetic diversity of many species as a result of clearcutting.
It is important to contrast secondary forests resulting from clear-cut
harvesting with those derived from natural disturbances. In the former , as
almost all standing biomass is usually removed, the resulting secondary
forest is structurally very simple and uniform. In contrast, natural secondary forest usually retains a substantial component of surviving oldgrowth individuals, standing dead trees, etc., which provide much greater
structural diversity and therefore species diversity.
Concern with forest fragmentation and the resultant extensive edge
effects, together with a recognition of the importance of structural diversity in forests, has led to the development of a philosophy termed "The
New Forestry" in the Pacific Northwest of the United States (Franklin ,
1989; Maser , 1990; Hansen et aI., 1991). Part of this philosophy calls for
large cut blocks, to minimize edge effects. Large trees, snags, and fallen
logs are retained on the harvested area to provide habitat for cavitynesting, amphibians , fungi, and other microorganisms.
In British Columbia, a substantial amount of effort is being devoted
to designing management strategies that are effective in maintaining
biodiversity. The provincial government has recently developed a management strategy proposal for the coastal region that integrates a system
of reserves with appropriate practices on managed land outside reserves.
The principles of ecosystem management and a consensus-building approach to decision making are key factors in the strategy (Pojar &
Hamilton, 1993). The ecological reserve component of this management
strategy seeks to protect a minimum of 10 to 12% of old-growth forest in
each forested site series, with rare ecosystems being overrepresented
365
Obviously, the impact of clearcutting is not a simple reduction in
species diversity, but rather a differential effect , with some old-growth
dependent species of plants and animals being lost from the system,
presumably until suitable environmental conditions are restored. However, the scale and pattern of clearcuts are also vitally important in
determining the response of different species to disturbance. The resultant
spatial heterogeneity and fragmentation of the landscape have significant
impact of species diversity and abundance. Fragments smaller than a
species' home range will result in a reduction in abundance of that
species, or its complete elimination. The ecosystem itself may then be
threatened with destruction. Research on boreal fragmentation in Sweden
has demonstrated that 1 ha reserves that are required by law are composed
entirely of edge habitat, and therefore do not function as forest ecosystems
(Dr. Per-Anders Esseen, personal communication). Because edge effects
penetrate some distance into the remaining forest, even a low intensity of
clearcutting can cause substantial habitat fragmentation (Hansen, Spies,
Swanson et aI., 1991). Pielou (1990) has also called attention to the
potential loss of genetically distinct demes , and the consequent impact on
genetic diversity of many species as a result of clearcutting.
It is important to contrast secondary forests resulting from clear-cut
harvesting with those derived from natural disturbances. In the former , as
almost all standing biomass is usually removed, the resulting secondary
forest is structurally very simple and uniform. In contrast, natural secondary forest usually retains a substantial component of surviving oldgrowth individuals, standing dead trees, etc., which provide much greater
structural diversity and therefore species diversity.
Concern with forest fragmentation and the resultant extensive edge
effects, together with a recognition of the importance of structural diversity in forests, has led to the development of a philosophy termed "The
New Forestry" in the Pacific Northwest of the United States (Franklin ,
1989; Maser , 1990; Hansen et aI., 1991). Part of this philosophy calls for
large cut blocks, to minimize edge effects. Large trees, snags, and fallen
logs are retained on the harvested area to provide habitat for cavitynesting, amphibians , fungi, and other microorganisms.
In British Columbia, a substantial amount of effort is being devoted
to designing management strategies that are effective in maintaining
biodiversity. The provincial government has recently developed a management strategy proposal for the coastal region that integrates a system
of reserves with appropriate practices on managed land outside reserves.
The principles of ecosystem management and a consensus-building approach to decision making are key factors in the strategy (Pojar &
Hamilton, 1993). The ecological reserve component of this management
strategy seeks to protect a minimum of 10 to 12% of old-growth forest in
each forested site series, with rare ecosystems being overrepresented