Present-Day Environments and Climate Change - Mountains and Plains: The Ecology of Wyoming Landscapes - page 34

topography influences growing season length and
mean temperature by causing the flow of heavier cold
air from mountain slopes to lower elevations, often
along waterways. this airflow can create temperature
inversions, that is, warmer temperatures on mountain
slopes than in the adjacent lowlands—the reverse of what
is normally expected. thus, the cities of Jackson and
cheyenne are at about the same elevation—6,209 feet
and 6,053 feet, respectively—but Jackson is much cooler
because of its location in Jackson Hole, which traps cold
air flowing downward from the nearby tetons. 11
one of the most significant effects of temperature is
on the potential rate of evapotranspiration—evaporation
from soil and open water plus the amount of water
evaporated on the interior of plant leaves and lost as
vapor through the stomata. Higher temperature and
lower humidity cause higher evapotranspiration, which
leads to summer drought stress for plants and animals.
the potential evapotranspiration, which can be calcu-
lated from temperature and solar radiation, generally is
greater than annual precipitation in the plains, basins,
and foothills—indicating dry conditions, because more
water can be evaporated than usually is available. in con-
trast, potential evapotranspiration in the mountains is
less than annual precipitation, creating relatively moist
conditions and the potential for streamflow. in the
mountains, where more precipitation usually falls than
evaporates, there is the potential for loss of nutrients as
they are dissolved in water moving through the soil pro-
file, a process known as leaching. only about 10 percent
of Wyoming has a precipitation-evaporation ratio greater
than one. 12 climate change surely will alter the precipi-
tation-evaporation ratio, which will lead to subsequent
changes in all ecosystems—including croplands.
topography and wind play an important role in
controlling water availability. South slopes are warmer
than north slopes, enabling more evapotranspiration,
and wind accelerates evapotranspiration and leads
to snow redistribution and sublimation. Areas blown
free of snow are drier during the growing season; areas
where snow accumulates are wetter. Strong winds are
common in Wyoming, especially in the south, where
the prevailing westerly winds are funneled through
the Rocky Mountains at a low point in the continental
Divide (generally along interstate 80). 13 this wind pat-
tern has contributed to the development of a narrow
band of sand dunes that is 100 miles long or more (see

chapter 8). the greatest potential for wind-generated
electricity is in the south, especially in the southeastern
quarter of the state. 14

Soil Characteristics

Plant growth, crop production, and the carrying capaci-
ties for wildlife and livestock depend on the nature of
the soil—a matrix of organic matter, clay, silt, sand,
and stones, teeming with microorganisms, inverte-
brates, and roots, and mixed periodically by burrowing
mammals, such as prairie dogs, ground squirrels, and
gophers. indeed, the amount of energy consumed by
belowground organisms in grassland ecosystems can
exceed the amount used by animals aboveground (see
chapter 6). every spoonful of soil contains millions of
organisms, including bacteria, fungi, yeasts, protozo-
ans, nematodes, and insect larvae. these mostly minus-
cule organisms contribute immensely to the structure
and fertility of the soil. Food webs belowground are
equally as complex and interesting as those above-
ground, though much more difficult to study.
A multitude of different soils exists in the region,
caused by the interactions over thousands of years of
varying climate, topography, rock substrate (parent
material), and plant and animal life (see appendix B).
Sometimes the soils change gradually from one place
to another, forming a gradient from comparatively dry
grasslands to relatively moist meadows. in other places,
the soils change abruptly because of abrupt changes
in topography or the rock type from which soil min-
erals are derived. Some soils are shallow and not well
developed, largely because of recent glaciation in the
mountains, or an abundance of erodible slopes and a
comparatively dry, cool climate not conducive to soil
formation.
the physical and chemical characteristics of soils are
heavily influenced by the nature of the parent material,
whether bedrock or transported sediments. igneous and
metamorphic rocks (such as granite, basalt, quartzite,
and rhyolite) are found primarily in the mountains.
they weather slowly, and consequently the soils are
usually shallow and coarse. Glacial moraines also lead
to the development of coarse soils. Sandstones and
limestones are resistant to weathering, often forming
escarpments and ridges with shallow soils. Where suf-
ficient weathering has occurred, sandstones contribute