wildlife. Livestock grazing is the fifth-rated threat to endangered plant species,
the fourth leading threat for all endangered wildlife, and the number one threat to
all endangered species in arid regions of the United States.
Figure 7.9 Endangered plant species as a function of biomeDesertification
Desertification is the conversion of marginal rangeland or cropland to a more
desert-like land type. It is often caused by overgrazing, soil erosion, prolonged
drought, or climate changes as well as the overuse of available resources such as
nutrients and water. Desertification proceeds with the following steps: First,
overgrazing results in animals eating all available plant life. Next, rain washes
away the trampled soil, since nothing holds back water anymore. Wells, springs,
and other sources of water dry up and what vegetation that is left dies from
drought or is taken for firewood. Then weeds that are unsuitable for grazing may
begin to take over, and the ground becomes unsuitable for seed germination.
Finally, wind and dry heat blow away the topsoil.