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rooted plants can also benefit from water that percolates
to greater depths after snowmelt or heavy spring rains. 11
While studying grassland root systems, Weaver would
sometimes dig by hand to a depth of 10 feet or more.
on at least once occasion he decided it was prudent to
abandon the trench because of caving soil. in a sense,
the grassland is the reverse of a forest, where vertical
stratification exists aboveground, with trees above the
shrubs and herbaceous plants in the understory. For-
est ecologists must watch for falling branches and even
whole trees, whereas grassland ecologists think more
about being buried in their trenches.
Grassland plants also partition resources season-
ally, with cool-season plants completing their growth
by early summer or in the fall (when moisture is avail-
able), and warm-season plants growing in the summer
(until moisture becomes limiting). Junegrass, threadleaf
sedge, and western wheatgrass are examples of cool-
season species; blue grama, buffalo grass, and little
bluestem are examples of warm-season plants. 12 this
differentiation is based on their physiological charac-
teristics. cool-season species commonly have lower
optimal temperatures for photosynthesis and use c 3
metabolism. Such plants are usually less tolerant of high
temperatures, thus growing early in the spring before
water stress develops. in contrast, warm-season species
have a higher optimal temperature for photosynthesis,
can tolerate higher light intensities, and have a higher
water-use efficiency (that is, more photosynthesis per
unit of water uptake)—all characteristics of c 4 metabo-
lism. the separation of grasses into c 3 and c 4 species
has stimulated great interest among biologists and land
managers, but it is only one of many ways that grass-
land plants are adapted to their environment.
Such differences in physiology also appear to affect
responses to grazing and geographic distribution. With
regard to grazing, a critical time for ranchers and their
livestock is in the spring, when hay supplies may be low
and there is little new forage production on rangelands.
the first plants to become green are the cool-season c 3
species—the plants most likely to be grazed first. the
warm-season species become important later, but by
that time there is more food available and less intense
grazing pressure on any one group. consequently,
repetitive early-spring grazing commonly leads to a
decline in c 3 species and an increase in some warm-
table 6.1. Some characteristic mammals, birds, and rep-
tiles found in grasslands, shrublands, and escarpments at
low elevations
MAMMALS
Badger
Bobcat
chipmunk, least
cottontail, desert
cottontail, nuttall's
coyote
Deer, mule
Fox, red
Fox, swift
Ferret, black-footed a
Ground squirrel,
thirteen-lined
Ground squirrel, Wyoming
Jackrabbit, black-tailed b
Jackrabbit, white-tailed c
Mouse, deer
Mouse, northern
grasshopper
Pocket gopher, northern
Prairie dog, black-tailed b
Prairie dog, white-tailed c
Pronghorn
Woodrat, bushy-tailed
BiRDS
Bluebird, mountain
Bunting, lark
eagle, golden
Falcon, prairie
Grouse, sage
Harrier, northern
Hawk, red-tailed
Jay, pinyon
Kestrel, American
Lark, horned
Longspur, Mccown's
Meadowlark, western
nighthawk, common
owl, burrowing
Sparrow, Brewer's
Sparrow, lark
Sparrow, sage
Sparrow, vesper
thrasher, sage
towhee, green-tailed
Vulture, turkey
RePtiLeS
Bullsnake
Rattlesnake, prairie
Lizard, northern sagebrush
Lizard, spiny
a now rare.
b eastern grasslands of Wyoming.
c Western two-thirds of Wyoming.
found that the root systems of some plants are mostly
deep, whereas others are mostly shallow. 10 in this way,
neighboring plants tap different parts of the soil for
water and nutrients. to illustrate, 85 percent of blue
grama roots are in the top 8 inches of soil. neighbor-
ing plants with deep root systems, down to 3 feet or
more, include scarlet globemallow, skeleton plant, and
slimflower scurfpea. All plants depend to some extent
on surface soil derived from summer rain, but deeper-
 
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