Environmental Engineering Reference
In-Depth Information
and future climate.This modeling predicts some significant northward shifts
in major vegetation communities within the continental United States. For
example, the eastern United States is expected to lose much of its cool-tem-
perate mixed forest because it is expected to shift northward into Canada.
This will be replaced by expansion of a warm temperate mixed forest that
is currently characteristic of southeastern United States. Prairie habitats that
characterize north-central states will be replaced by range expansion of
prairie habitat that is characteristic of south-central states.Temperate arid
shrub lands, alpine tundra, and taiga in the intermountain region will dis-
appear from most of their current range.
The effect of these vegetation shifts on wildlife species distributions was
evaluated by following several steps. First, maps of current species distribu-
tions were overlaid onto a map of the current continental United States dis-
tribution of ecosystem types and the statistical relationship between them
was estimated.This statistical estimator was used in conjunction with a new
map, depicting ecosystem change in the face of climate warming, to assess cli-
mate impacts on the two wildlife species. In general, white-tailed deer, east-
ern chipmunks, and Columbian ground squirrels were expected to retain the
same range size or increase it.The geographic distribution was expected to
shift somewhat for white-tailed deer, almost entirely for Columbian ground
squirrels, and not at all for eastern chipmunks. Elk were expected to suffer
the greatest impact with a 93 percent loss of current range and no prospect
for range expansion or redistribution (figure 3.4). Consequently, some
species are expected to be very sensitive to climate change with consequent
range reduction; others will be able to tolerate changing climate.This type
of analysis can target which species are most likely to be sensitive.
Global climate change is not only a future concern.With increases in
temperatures around the world of an average of 0.5° C in the past one hun-
dred years (IPCC 1996), climate change has had contemporary effects on
some wildlife populations. In the northern hemisphere, winter minimum
temperatures have risen 3° C and spring maximum temperatures have risen
1.4° C since the middle of the twentieth century (Easterling 1997). More
frequently, we are encountering signals that hint that climate change is al-
ready altering the distribution of wildlife. Studies that have compared range
distributions over this time period shed light on the direction and extent of
wildlife shifts in response to warming trends.
It appears that there has been a significant northern shift in geographic
range for several species of birds, insects, and mammals. For instance, nearly
