occurs in conjunction with overgrazing,
once-fertile rangeland may be converted to
desert as reduced grass cover allows winds to
erode the soil. Even when the rains return,
the degradation may be so extensive that the
land cannot recover. Water erosion removes
the little remaining topsoil, and the sand left
behind forms dunes.
Land degradation is both a natural and
a human-induced process that decreases the
future ability of the land to support crops
or livestock. This progressive degradation,
which induces unproductive desert-like con-
ditions on formerly productive rangeland
(or tropical dry forest), is desertification (Figure 13.9).
It reduces the agricultural productivity of economically
valuable land, forces out many organisms, and threatens
endangered species. Worldwide, desertification seems to
be on the increase. The United Nations estimates thatis exceeded, overgrazing of grasses and other
plants occurs. When plants die, the ground is
left barren, and the exposed soil is susceptible
to erosion. Sometimes plants that do not natu-
rally grow in a rangeland but that can tolerate
the depleted soil invade an overgrazed area. In
parts of the Texas Hill Country that were over-
grazed, junipers—which are not good forage
food—replaced the lush grasses.
Most of the world’s rangelands lie in semiarid
areas that have natural extended droughts. Dur-
ing dry periods, the carrying capacity of the
rangeland is considerably lower because the
lack of precipitation reduces plant productivity.
Native grasses in these dry lands can survive severe
drought: The aboveground portion of the plant dies
back, but the extensive root system remains alive and
holds the soil in place. When the rains return, the roots
develop new shoots. But when an extended drought
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Livestock in Mali, Africa, have eaten all the ground cover. The dead trees were stripped of branches to feed
livestock and provide firewood. Overgrazing, in combination with extended drought, as well as with
over exploitation by desperately poor people, is increasing the amount of unproductive desert area in the Sahel.
overgrazing
A situation that
occurs when too
many grazing animals
consume the plants
in a particular area,
leaving the vegetation
destroyed and unable
to recover.
desertification
Degradation of once-
fertile rangeland or
tropical dry forest into
nonproductive desert.K. Tumanowicz/ScienceSourceNG MapsGlobal
LocatorSAHEL