Grasslands - Mountains and Plains: The Ecology of Wyoming Landscapes - page 85

nial and herbaceous, having their perennating buds at
or just below the soil surface. this growth form is the
result of several factors: first, the semi-arid nature of
mixed-grass prairie limits the production of woody
stems aboveground. Second, and perhaps most impor-
tant, is the frequency of fires in grasslands. Plants with
buds at or near the soil surface are less likely to be
killed, because the soil surface temperature during a
fire is relatively low. Most buds survive, and only the
herbaceous stems and leaves are burned. After the fire,
the buds sprout and grow rapidly. third, plants with
their buds near the soil are well adapted to tolerate
grazing by large herbivores, which 10,000 years ago
included the camel and horse as well as bison, elk, and
pronghorn. Buds close to the ground, or buried in the
soil, are less likely to be eaten by the herbivores. only
the easily regenerated stems and leaves are consumed
(fig. 6.4).
the ability to replace leaves and stems that have
been eaten or burned depends on the presence of spe-
cial meristems—tissues capable of cell division and
new growth—and the capacity for energy storage in
the undamaged part of the plant belowground. the
meristems are contained in dormant buds on rhizomes
and root crowns, which are stimulated by herbivory to
produce new stems and leaves. Another way that grass
leaves can be replaced is through intercalary meristems,
which are tissues capable of cell division that occur near
the bases of the leaves and some stems. As grass leaves
are eaten, new leaf tissue is produced by the leaf itself.
no buds are involved. 7
Regrowth, whether from buds or intercalary meri-
stems, requires energy stored as carbohydrates in roots,
rhizomes, bulbs, and corms. carbohydrates are pro-
duced by photosynthesis aboveground but are mostly
moved belowground soon thereafter. considering that
75 percent or more of grassland plant biomass is below-
ground, there is a large amount of energy available to
keep the plant alive and enable the production of new
leaves and stems. 8 of course, plants die from a lack of
energy if fire, herbivory, or drought are too frequent to
allow for the replacement of the stored energy spent in
previous episodes of regrowth.
Most grassland plants have characteristics of xero-
phytes, that is, plants adapted to dry environments.
typically, they have small or narrow leaves, and some

Fig. 6.2. An aerial view of grasslands in the Laramie Basin
showing fairy rings that are about 30 feet in diameter, cre-
ated by fungi that grow outward. A flush of nutrients is made
available as the fungi die and decompose, just inward from
the zone of major fungal activity, thereby stimulating plant
growth. elevation 7,300 feet.

for the largest group of herbivores in the ecosystem—
invertebrates. As the roots and other forms of life die,
they become part of the soil's organic matter. Some
plants have deep roots for extracting moisture from
throughout the soil profile, whereas others have shal-
low roots to take advantage of light showers that wet
only the surface soil. Generally, about 70 percent of
the roots are within the top 4 inches.
throughout the western Great Plains, grassland
plants have experienced extended periods of drought,
recurring fire, and grazing by herbivores. these envi-
ronmental factors led to a community composed
largely of grasses but with a substantial number of
sedges and forbs. notably, most of the plants are peren-