124
Paul B. Alaback
which the ecological characteristics of managed forests have been directly
contrasted with those of natural secondary forest. These comparisons are
needed to identify the linkage between structure and function in the
maintenance of biological diversity in these forests and to provide
guidance for land managers on how to enhance the functional characteristics of managed forests.
Comparisons with Ecological Analogs in the Southern Hemisphere
The temperate rainforests of North America would be expected to
be more diverse than their ecological equivalents in the Southern
Hemisphere, because of their recent connection to a large and diverse
temperate forest biome and the diversity of climates that occur in the
region. Several other complicating factors both in history and current climate appear to counteract this influence, resulting in roughly
equivalent species diversity in the principal rainforest regions of the
world.
As shown in Figure 7.1, Chile has a significantly more equitable climate
than ecologically equivalent ecosystems in North America , both in terms
of annual variation in temperature and in distribution of rainfall. Chile
also has a significantly more exposed coastline, with higher storm frequencies and higher wind velocities, resulting in a much more extensive
subpolar rainforest than in North America. Seasonal rainforest , arising
primarily as a transitional type between more northerly drier climates and
more continental climates, is much more extensive in North America ,
perhaps again as a result of the greater continental mass in temperate
North America as compared to South America. It appears that the
Chilean flora has a close association with tropical and subtropical regions
to the north , from which many of the species probably evolved. Although
regional vascular plant diversity in Chile appears to be substantially less
than that in North America , forest species richness is equal or greater in
Chile than in North America (Arroyo et aL, this volume). See Table 7.1.
In the perhumid zone of both hemispheres, approximately 250 species
occur in forest habitats (Arroyo et aL, this volume; Martin , 1989). One of
the principal contrasts in the forest flora of the two regions is much higher
regional endemism (or smaller average geographic distributions) in Chile,
whereas high regional endemism occurs only in the warm temperate zone
in the Pacific coastal forest of North America.
The rainfore sts of Tasmania provide an interesting contrast with those
of North America and Chile with respect to the influence of both evolutionary and human factors on biodiversity patterns (Brown & Read, this
volume; Jarman et aI., 1991; Read et aL, 1990). Tasmania has a relatively
isolated rainforest flora, with large extinctions associated with the
development of cooler climates since the Tertiary. Poor migration cor-
Paul B. Alaback
which the ecological characteristics of managed forests have been directly
contrasted with those of natural secondary forest. These comparisons are
needed to identify the linkage between structure and function in the
maintenance of biological diversity in these forests and to provide
guidance for land managers on how to enhance the functional characteristics of managed forests.
Comparisons with Ecological Analogs in the Southern Hemisphere
The temperate rainforests of North America would be expected to
be more diverse than their ecological equivalents in the Southern
Hemisphere, because of their recent connection to a large and diverse
temperate forest biome and the diversity of climates that occur in the
region. Several other complicating factors both in history and current climate appear to counteract this influence, resulting in roughly
equivalent species diversity in the principal rainforest regions of the
world.
As shown in Figure 7.1, Chile has a significantly more equitable climate
than ecologically equivalent ecosystems in North America , both in terms
of annual variation in temperature and in distribution of rainfall. Chile
also has a significantly more exposed coastline, with higher storm frequencies and higher wind velocities, resulting in a much more extensive
subpolar rainforest than in North America. Seasonal rainforest , arising
primarily as a transitional type between more northerly drier climates and
more continental climates, is much more extensive in North America ,
perhaps again as a result of the greater continental mass in temperate
North America as compared to South America. It appears that the
Chilean flora has a close association with tropical and subtropical regions
to the north , from which many of the species probably evolved. Although
regional vascular plant diversity in Chile appears to be substantially less
than that in North America , forest species richness is equal or greater in
Chile than in North America (Arroyo et aL, this volume). See Table 7.1.
In the perhumid zone of both hemispheres, approximately 250 species
occur in forest habitats (Arroyo et aL, this volume; Martin , 1989). One of
the principal contrasts in the forest flora of the two regions is much higher
regional endemism (or smaller average geographic distributions) in Chile,
whereas high regional endemism occurs only in the warm temperate zone
in the Pacific coastal forest of North America.
The rainfore sts of Tasmania provide an interesting contrast with those
of North America and Chile with respect to the influence of both evolutionary and human factors on biodiversity patterns (Brown & Read, this
volume; Jarman et aI., 1991; Read et aL, 1990). Tasmania has a relatively
isolated rainforest flora, with large extinctions associated with the
development of cooler climates since the Tertiary. Poor migration cor-