Ecoregions and Climate Change
10
Ecoregions are large, region-scale ecosystems—
ecoregions such as the Sonoran Desert. These
regions are primarily defined by climatic
conditions and on the prevailing plant formations
determined by those conditions. Climate, as a
source of energy and water, acts as the primary
control for ecosystem distribution, including
ecoregions. As climate changes, so do
ecosystems, as do ancient shore lines of lakes in
a desert attest (Fig. 10.1). Recognizing that climate is a principal controlling factor for
ecosystems subsequently identifies the need to
study the potential climatic change in terms of
its ramifications to the Earth’s terrestrial
ecosystems. Knowing where ecological shifts
will most likely occur and consequences
associated with such shifts are prerequisite to
productively evaluating these changes and how
they affect decisions regarding resource development and management.
10.1 Long-Term Climate Change
The distribution of plant and animal communities,
and indeed of entire ecoregions, has varied
tremendously with past changes in climate, even
in the absence of man’s activities. The spatial
distribution of life forms today as a function of
latitude, continental position, and elevation looks
very different compared to those of 5,000 or
10,000 years before the present (BP).
Climatic changes on the Earth during the past
500,000 years have been dramatic (Fig. 10.2).
Each glacial–interglacial cycle is about 100,000
years in duration, with 90,000 years of gradual
climatic cooling followed by rapid warming and
10,000 years of interglacial warmth. The peak of
the last glacial period, or ice age, was about
18,000 years BP and ended approximately
10,000 years BP.
During the glacial periods, the world’s ice
caps were greatly expanded. On the periphery
of the expansive ice sheets, were correspondingly great areas of open tundra frequently
underlain by permafrost. The areas of forest that
form the natural vegetation of much of north and
eastern North America as well as western Europe
today were largely occupied by cold, rather dry
tundra and steppe. A representation of the expansion and contraction of ecoclimatic zones is
given in Fig. 10.3, which shows the migration
of zonal belts in relation to glacial advance and
retreat. Geological evidence indicates that, at
certain times in the past, more water accumulated
in low-latitude desert areas: huge lakes, for
example, filled the now largely dry basins of the
southwest United States. However, in other
areas, the glacial periods were characterized,
not by increased humidity, but by reduced precipitation. The most spectacular evidence for this
is the great expansion of sand dunes in low
latitudes: studies of air photos and satellite imagery indicate that degraded ancient dunes lie in
areas that are now quite moist. Today, about
10 % of the land area between 30
N and 30
S
is covered by active sand deserts. During the last
great glacial advance, about 18,000 years ago,
R.G. Bailey, Ecoregions, DOI 10.1007/978-1-4939-0524-9_10, # Springer Science+Media, LLC 2014
95
10
Ecoregions are large, region-scale ecosystems—
ecoregions such as the Sonoran Desert. These
regions are primarily defined by climatic
conditions and on the prevailing plant formations
determined by those conditions. Climate, as a
source of energy and water, acts as the primary
control for ecosystem distribution, including
ecoregions. As climate changes, so do
ecosystems, as do ancient shore lines of lakes in
a desert attest (Fig. 10.1). Recognizing that climate is a principal controlling factor for
ecosystems subsequently identifies the need to
study the potential climatic change in terms of
its ramifications to the Earth’s terrestrial
ecosystems. Knowing where ecological shifts
will most likely occur and consequences
associated with such shifts are prerequisite to
productively evaluating these changes and how
they affect decisions regarding resource development and management.
10.1 Long-Term Climate Change
The distribution of plant and animal communities,
and indeed of entire ecoregions, has varied
tremendously with past changes in climate, even
in the absence of man’s activities. The spatial
distribution of life forms today as a function of
latitude, continental position, and elevation looks
very different compared to those of 5,000 or
10,000 years before the present (BP).
Climatic changes on the Earth during the past
500,000 years have been dramatic (Fig. 10.2).
Each glacial–interglacial cycle is about 100,000
years in duration, with 90,000 years of gradual
climatic cooling followed by rapid warming and
10,000 years of interglacial warmth. The peak of
the last glacial period, or ice age, was about
18,000 years BP and ended approximately
10,000 years BP.
During the glacial periods, the world’s ice
caps were greatly expanded. On the periphery
of the expansive ice sheets, were correspondingly great areas of open tundra frequently
underlain by permafrost. The areas of forest that
form the natural vegetation of much of north and
eastern North America as well as western Europe
today were largely occupied by cold, rather dry
tundra and steppe. A representation of the expansion and contraction of ecoclimatic zones is
given in Fig. 10.3, which shows the migration
of zonal belts in relation to glacial advance and
retreat. Geological evidence indicates that, at
certain times in the past, more water accumulated
in low-latitude desert areas: huge lakes, for
example, filled the now largely dry basins of the
southwest United States. However, in other
areas, the glacial periods were characterized,
not by increased humidity, but by reduced precipitation. The most spectacular evidence for this
is the great expansion of sand dunes in low
latitudes: studies of air photos and satellite imagery indicate that degraded ancient dunes lie in
areas that are now quite moist. Today, about
10 % of the land area between 30
N and 30
S
is covered by active sand deserts. During the last
great glacial advance, about 18,000 years ago,
R.G. Bailey, Ecoregions, DOI 10.1007/978-1-4939-0524-9_10, # Springer Science+Media, LLC 2014
95