354
T.J.B. Boyle
environment (Alaback , Chapter 7). West coast forests are also unique in
terms of their successional history, which is dominated by such small-scale
disturbances as individual tree deaths and local wind throws. This results
in the maintenance of a very high proportion of the forest in "oldgrowth" conditions , with high-structural diversity. Finally, the physiographic complexity of the region results in very high ecosystem diversity,
and consequently beta species diversity. Whilst this paper touches on
biodiversity in all of Canada's forests, the forests of the west coast are
given special attention.
Statusof Biological Diversity in Canada's Forests
Biodiversity covers the entire range of the hierarchy of biological organization, and this results in an inherent problem in its measurement
and monitoring. Biodiversity is usually divided into a three-to-five level
hierarchy (e.g., Cohen & Potter, 1993); here four levels are recognized:
genetic, species, community/ecosystem, and landscape diversity. There
are also a multitude of other ways of measuring or defining biodiversity.
Rather than considering biodiversity in terms of hierarchical organization,
it is also possible to characterize it in terms of ecological processes
or functions. Thus it is possible to assess trophic diversity, structural
diversity, or functional diversity (Franklin , 1988); and evolutionary, or
historical diversity (Arroyo et aI., Chapter 8). However , although this
latter group of terms may have great value for certain applications or for
examining particular aspects of biological systems, the genetic-speciesecosystem-landscape approach is conceptually simpler and easier to apply
at multiple spatial scales.
Genetic Diversity
Most west coast conifer species have high genetic diversity, typical of
tree species generally (Hamrick , Mitton, & Linhart , 1981), with the
notable exception of western red cedar (Thuja pUcata) (Copes, 1981). For
example, estimates of among-population genetic variation for Sitka spruce
(Picea sitchensis) (Yeh & El-Kassaby, 1980) were typical of those for
all conifers (Hamrick et aI., 1981). Two species of west coast conifer
that have been studied more intensively than any other are Douglas fir
(Pseudotsuga menziesii) and lodgepole pine (Pinus contorta). These
species both have large latitudinal ranges as well as coastal and inland
varieties. For both species, there is no indication of differences in genetic
structure among coastal and inland varieties (EI-Kassaby, 1990), apart
from one study of inland Douglas fir from the southern end of its range in
the United States, where among-population differences are much larger
than elsewhere (Li & Adams , 1988). EI-Kassaby and Sziklai (1982)
T.J.B. Boyle
environment (Alaback , Chapter 7). West coast forests are also unique in
terms of their successional history, which is dominated by such small-scale
disturbances as individual tree deaths and local wind throws. This results
in the maintenance of a very high proportion of the forest in "oldgrowth" conditions , with high-structural diversity. Finally, the physiographic complexity of the region results in very high ecosystem diversity,
and consequently beta species diversity. Whilst this paper touches on
biodiversity in all of Canada's forests, the forests of the west coast are
given special attention.
Statusof Biological Diversity in Canada's Forests
Biodiversity covers the entire range of the hierarchy of biological organization, and this results in an inherent problem in its measurement
and monitoring. Biodiversity is usually divided into a three-to-five level
hierarchy (e.g., Cohen & Potter, 1993); here four levels are recognized:
genetic, species, community/ecosystem, and landscape diversity. There
are also a multitude of other ways of measuring or defining biodiversity.
Rather than considering biodiversity in terms of hierarchical organization,
it is also possible to characterize it in terms of ecological processes
or functions. Thus it is possible to assess trophic diversity, structural
diversity, or functional diversity (Franklin , 1988); and evolutionary, or
historical diversity (Arroyo et aI., Chapter 8). However , although this
latter group of terms may have great value for certain applications or for
examining particular aspects of biological systems, the genetic-speciesecosystem-landscape approach is conceptually simpler and easier to apply
at multiple spatial scales.
Genetic Diversity
Most west coast conifer species have high genetic diversity, typical of
tree species generally (Hamrick , Mitton, & Linhart , 1981), with the
notable exception of western red cedar (Thuja pUcata) (Copes, 1981). For
example, estimates of among-population genetic variation for Sitka spruce
(Picea sitchensis) (Yeh & El-Kassaby, 1980) were typical of those for
all conifers (Hamrick et aI., 1981). Two species of west coast conifer
that have been studied more intensively than any other are Douglas fir
(Pseudotsuga menziesii) and lodgepole pine (Pinus contorta). These
species both have large latitudinal ranges as well as coastal and inland
varieties. For both species, there is no indication of differences in genetic
structure among coastal and inland varieties (EI-Kassaby, 1990), apart
from one study of inland Douglas fir from the southern end of its range in
the United States, where among-population differences are much larger
than elsewhere (Li & Adams , 1988). EI-Kassaby and Sziklai (1982)