106
Paul B. Alaback
further underscoring the need to understand the region in a broad-scale
sense.
The west coast is one of the last major forest regions to be exploited in
North America and as such contains some of the greatest remaining
examples of pristine forest on the continent. This region provides one of
the best areas for testing ideas about how natural landscapes are structured
and how changes in landscape structure influence ecological processes ,
since both managed and pristine landscapes are present here. The temperate rainforest region is of particular interest for biodiversity studies ,
since it encompasses a broad range of landscape types both within
and between latitudes and includes both Pleistocene and recent glacial
environments.
In this chapter, we present an overview and synthesis on vegetation
biodiversity patterns in coastal-forest vegetation from the southern limit
of continuous forest in the redwood region in northern California north to
the limit of coastal forest in central Alaska. The key focus of this paper is
on the temperate rainforest region of the coastline, which includes most
of the coastal forest in the north but only a narrow belt of forest in the
south. Basic patterns of forest biodiversity and forest genetics are discussed
to provide a basis for prioritizing research needs on how better to predict
the effects of global climate change across this broad region and to
identify data gaps. This synthesis should also provide guidance to resource
managers on the kinds of information needed to understand how best to
adapt ecosystems or landscapes to the uncertain future presented with
climate change.
Physical Environment
The gradient from 38°N to 61°N across western North America extends
from fog-drenched, almost Mediterranean climates to perpetually wet
rainforests and tundra. For our purposes, rainforest is defined to include
maritime climates with 1400mm annual precipitation or greater, and with
cool temperatures year-round. For convenience of discussion, North
American'rainforests are divided into four principal zones: 1) the subpolar rainforest zone (59°N-61°N), where heavy precipitation occurs
during most months (summer rainfall >20% of annual), summers are
very cool, and sea-level snow is common; 2) the perhumid rainforest zone
(50 0N-58°N), where summer precipitation is common (> 10% of annual),
summers are cool, and snow is transient in the winter ; 3) the seasonal
rainforest zone (43°N-500N) , where summer droughts and fire are
common and less than 10% of annual precipitation occurs during the
summer; and 4) the warm temperate rainforest zone (38°N-43°N), where
extended droughts and fire can occur at any time of the year and 5% or
less of annual rainfall occurs during summer (Alaback , 1991; Franklin &
Paul B. Alaback
further underscoring the need to understand the region in a broad-scale
sense.
The west coast is one of the last major forest regions to be exploited in
North America and as such contains some of the greatest remaining
examples of pristine forest on the continent. This region provides one of
the best areas for testing ideas about how natural landscapes are structured
and how changes in landscape structure influence ecological processes ,
since both managed and pristine landscapes are present here. The temperate rainforest region is of particular interest for biodiversity studies ,
since it encompasses a broad range of landscape types both within
and between latitudes and includes both Pleistocene and recent glacial
environments.
In this chapter, we present an overview and synthesis on vegetation
biodiversity patterns in coastal-forest vegetation from the southern limit
of continuous forest in the redwood region in northern California north to
the limit of coastal forest in central Alaska. The key focus of this paper is
on the temperate rainforest region of the coastline, which includes most
of the coastal forest in the north but only a narrow belt of forest in the
south. Basic patterns of forest biodiversity and forest genetics are discussed
to provide a basis for prioritizing research needs on how better to predict
the effects of global climate change across this broad region and to
identify data gaps. This synthesis should also provide guidance to resource
managers on the kinds of information needed to understand how best to
adapt ecosystems or landscapes to the uncertain future presented with
climate change.
Physical Environment
The gradient from 38°N to 61°N across western North America extends
from fog-drenched, almost Mediterranean climates to perpetually wet
rainforests and tundra. For our purposes, rainforest is defined to include
maritime climates with 1400mm annual precipitation or greater, and with
cool temperatures year-round. For convenience of discussion, North
American'rainforests are divided into four principal zones: 1) the subpolar rainforest zone (59°N-61°N), where heavy precipitation occurs
during most months (summer rainfall >20% of annual), summers are
very cool, and sea-level snow is common; 2) the perhumid rainforest zone
(50 0N-58°N), where summer precipitation is common (> 10% of annual),
summers are cool, and snow is transient in the winter ; 3) the seasonal
rainforest zone (43°N-500N) , where summer droughts and fire are
common and less than 10% of annual precipitation occurs during the
summer; and 4) the warm temperate rainforest zone (38°N-43°N), where
extended droughts and fire can occur at any time of the year and 5% or
less of annual rainfall occurs during summer (Alaback , 1991; Franklin &