Geoscience Reference
In-Depth Information
Fig. 7.16. the population of feral horses
commonly exceeds the carrying capac-
ity of the rangelands they occupy. Photo
by Ken Driese.
if cheatgrass has not become the widespread problem in
Wyoming that it is in the Great Basin, the explanation
may be partially because Wyoming plants evolved with
larger herds of bison. if true, native herbaceous plants
would have been more competitive and more resistant to
invasive species. As discussed for grasslands, maintain-
ing competitive stands of native species may be the best
strategy for excluding undesired plants (see chapter 6).
the management of Wyoming shrublands is more
refined today than it was a half-century ago, but the
impacts of excessive livestock grazing in those early
years probably exist to this day in some areas. Perhaps
the sagebrush-dominated rangelands most similar to
those of the mid-1800s are located some distance from
frequently used sources of water—too far away for
most cattle to use—or where fires have not always been
suppressed, or where the seeds of cheatgrass or other
invasive plants are not yet in the soil. Do such places
still exist? Debra Donahue, professor of law at the Uni-
versity of Wyoming, argues that, because of past and
ongoing environmental damage by livestock, there is a
legal mandate for stopping livestock grazing on public
lands. 88 Doing this even on public land only, she con-
tends, would facilitate the restoration of both the sage-
brush ecosystem and nearby riparian zones. Restoration
of sagebrush-dominated shrublands to their prehistoric
condition may be expecting too much, but it is plau-
sible that such initiatives will lead to better rangeland
condition in some places. Debate about the comparative
effects of native ungulates and domestic livestock will
continue. 89
Several species of horses evolved in north America,
but all became extinct about 10,000 years ago, along
with the camel, mastodon, saber-tooth tiger, and
numerous other large mammals (see chapter 2). Some
species survived in eurasia and were the ancestors of
modern day Equus caballus . Domestication began about
3000 bc . Horses were reintroduced to north America in
1539, when Hernando de Soto and his conquistadores
brought a herd of 220 to present-day Florida. Mov-
ing westward was difficult, even with horses, but the
Spaniards traveled a circuitous route to what are now
texas and new Mexico. Along the way, some of their
horses wandered off, were traded, or were stolen. indi-
ans obtained the horse in the 1600s, and by 1750 horses
were in canada. the horse caused dramatic changes in
the lifestyle of indigenous people, just as they have for
the many people who raise horses today for a multitude
of purposes. 90
Feral horses are now common on the shrublands of
the southwestern quarter of Wyoming and westward
into the Great Basin states (fig. 7.16). Some, known as
mustangs, are similar genetically to the horses brought
to America in the 1500s. With few predators to keep
their populations in check, these large herbivores
became, essentially, an invasive species, often forming
 
Search WWH ::




Custom Search