Present-Day Environments and Climate Change - Mountains and Plains: The Ecology of Wyoming Landscapes - page 27

Chapter 3 Present-Day
Environments and Climate
Change

Topography

Describing the environment in a way that is meaningful
for understanding the growth and abundance of plants,
animals, and other forms of life is one of the greatest
challenges faced by ecologists. convenient numbers
are sometimes calculated, such as monthly or seasonal
averages of temperature, but organisms respond to the
full complex of interacting environmental factors—
not to one individual factor or to statistical summa-
ries. Moreover, extremes are usually more important
than averages, and young individuals are less tolerant
of extremes. therefore, the distribution of a species
depends more on the environment prevailing when the
plants or animals were young—conditions that usually
are not known when the focus is on adult plants. Little
wonder, then, that correlations between environmental
variables and the presence or absence of a species are
sometimes hard to find. the challenge is to integrate
the diverse factors that determine whether an organism
will survive.
the environments of wetlands, grasslands, shrub-
lands, forests, tundra, and other kinds of ecosystems are
discussed in subsequent chapters. Here, general patterns
are described, with emphasis on the effects of topogra-
phy and elevation on precipitation, temperature, evapo-
ration, growing season length, soil characteristics, and
the nature and frequency of periodic disturbances. All
of these variables interact in determining the nature of
the ecosystem in a specific area—and all are affected by
climate change, the topic of the last section.

Wyoming landscapes span an elevational range of 10,758
feet, from the lowest point on the plains at 3,125 feet,
where the Belle Fourche River flows into South Dakota,
to the top of Gannett Peak at 13,809 feet. More than
one-third of the state is above 7,000 feet, and 10 per-
cent is above 9,000 feet (fig. 3.1). About fifty mountain
peaks are 13,000 feet or above, mostly in the Wind River
Mountains. Several major rivers originate in the state
and flow into the Missouri, colorado, or columbia river
drainages (see chapter 4).
elevation affects all environmental variables. tem-
perature decreases as one climbs, whereas annual pre-
cipitation generally increases. 1 these trends create a
cooler and relatively moist environment in the moun-
tains. Some groups of closely related plants have differ-
ent species adapted to lowland, foothill, montane, and
alpine environments (fig. 3.2). the effects of elevation,
however, are strongly moderated by the influences of
topography and the increased rates of evaporation that
occur at higher elevations because of lower atmospheric
pressure in the mountains. 2 thus, high south-facing
slopes that receive direct solar radiation throughout the
year sometimes are as dry as low-elevation deserts. in
contrast, north slopes at low elevations—cooler because
of less direct sunlight—have vegetation normally found
at higher elevations. Such observations have led ecolo-
gists to conclude that topographic position and degree
of exposure to direct sunlight are more important than

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