Geoscience Reference
In-Depth Information
big sagebrush germination, 22 an observation that may
explain why the plant is less common on saline soils.
A high percentage of big sagebrush seeds are viable
and germinate readily (80 percent or more). However,
seedlings survive only during favorable years and typi-
cally following a disturbance that reduces the competi-
tive ability of neighboring plants. 23 the age distribution
of a sagebrush population is therefore discontinuous; that
is, only a few age classes are represented. 24 conditions for
high growth rates early in the summer are essential, so
that the seedlings can develop a root system adequate to
cope with late-summer droughts. Jerry Schuman, mine-
land reclamation specialist, found that sowing too much
grass seed can lead to a level of competition from grasses
that reduces sagebrush seedling survival. 25
The Sagebrush Ecosystem
compared to grasslands, the distinguishing features
of sagebrush ecosystems are (1) the presence of an aro-
matic shrub with both shallow and deep roots and (2) a
large portion of the annual precipitation occurring in
the winter. otherwise, grasslands and sagebrush steppe
are similar:
Fig. 7.10. Snow frequently accumulates on the lee side of
shrubs, which probably increases the amount of water that
infiltrates the soil.
• plant growth (net primary productivity) is limited
by water availability and the length of the growing
season;
• most of the biomass and half or more of the herbiv-
ory is belowground;
• potential evapotranspiration usually is greater than
the annual precipitation;
• nutrients are rarely leached beyond the rooting zone;
• ire, drought, and burrowing animals are common
disturbances;
• plant and animal species have evolved to minimize
competition by using different resources and by us-
ing them at different times of the year; and
• coexisting herbivores, above- and belowground,
interact in complex ways to affect nutrient cycling
and plant growth.
Hydrology and Plant Growth
Drifted snow on the lee side of shrubs (fig. 7.10) can be a
significant supplement to soil water recharge, especially
on comparatively level sites, where accumulation is not
affected by topography. 26 Scientists and land managers
have learned that, without big sagebrush, relatively
more water and nutrients are available for the growth
of more palatable grasses and forbs, but overall, there
is probably less total water available and less total plant
growth than when the shrubs are present. Sagebrush
ecosystems have aboveground plant growth totaling
80-250 g/m 2 /year, which is higher than that for many
mixed-grass prairies in Wyoming. 27
Plant water availability may also be influenced by
the blackbody effect of shrubs that are above the snow
in winter. 28 Heat is absorbed by the shrub tops, caus-
ing snowmelt around the shrub more often than would
occur otherwise and creating a depression or well into
this section focuses on differences caused by the pres-
ence of an evergreen, deep-rooted shrub that is not able
to sprout—and what happens when it dies because of
burning or herbicides.
 
Search WWH ::




Custom Search