In Mongolia, livestock products, including live animals, milk, meat, wool
and hides, account for one-third of that country's gross domestic product.
In Africa much of the livestock is used to provide daily nourishment for
many rural populations who depend on their animals for sustenance. Those
of us whose livelihoods depend on grasslands are vitally aware of their
value, but many of us who only use the products these ecosystems provide
are not. We know that grasslands contain scenic landscapes and unique mixes
of species, but they are also home to nearly 800 million people. Grasslands
encompass the savannas of Africa, the grasslands of Australia, the cerrado
and campo of South America, the prairies of North America, and the steppes
of Central Asia.
Depleted grasslands in Mongolia.
Highly dynamic ecosystems, grasslands support flora, fauna, and human populations
worldwide. Grasslands provide food, energy, biodiversity conservation, carbon
storage, tourism, and habitats for endemic bird and wild herbivore species.
They also recycle water and build and maintain soil stabilization mechanisms.
However, in taking advantage of some of these goods and services, human
activities have had a devastating effect on grasslands.
How much grassland is left?
Estimates of grasslands' global extent range from 41 to 56 million square
kilometers (km2), covering from 31% to 43% of Earth's land surface. Why
the broad estimates? Some researchers include more (or less) tundra or shrubland
in their assessments. Broadly defined, grasslands are "areas dominated by
grassy vegetation and maintained by fire, grazing, and drought or freezing
temperatures." If it weren't for these maintenance factors, trees and shrubs
in many grasslands would increase and the grassland could eventually become
In central North America, tall-grass prairie has decreased by nearly 97%,
converted to urban and agricultural areas. Conversion, particularly to croplands
and other agroecosystems, has been the primary reason for the diminishing
extent of grasslands globally. In selected grassland ecoregions, conversion
to croplands has been as high as 76% in South America and from 20% to 40%
in other regions.
The Global Extent of Grasslands
(click on image to enlarge)
What are some of the most important goods and services
Food (meat) Domestic and wild animals
sustained by grassland forage provide vital sources of meat, milk
and other products.
Biodiversity Grasslands comprise 35
of 136 terrestrial ecoregions identified as outstanding examples
of diverse ecosystems.
Food (cereals) Wheat, rice, rye, and
other major crop grains originated in grasslands, a prime source
of crop genetic resources.
Carbon storage Grasslands store about
34% or the terrestrial global stock of carbon, most of it in the
soil rather than in vegetation.
Energy Fuelwood and windfarms are important
sources of energy originating in grasslands.
Tourism Developing countries with vast
grasslands reap substantial economic gains from grassland recreation
What are the primary pressures threatening grassland ecosystems?
The primary pressure on grassland ecosystems is outright
conversion to other uses. Conversion to agroecosystems and urban areas
especially brings pressures from the infrastructure needed to support
these new systems. Road building causes fragmentation, which can degrade
habitat and adversely impact biodiversity. Furthermore, fragmentation
caused by the spread of nonnative species can not only disrupt patterns
of growth of native species but also degrade freshwater systems within
grasslands, as we saw in South
Grassland Blocks in the Great Plains (click on
image to enlarge)
The most severe modification of grassland ecosystems, however,
may be desertification. Scant rains in arid grassland ecosystems make
these ecosystems particularly susceptible to damage from human management
and slower to recover from degradation. Desertification results when land
is severely degraded in arid, semiarid, and dry sub-humid areas. It's
caused by factors that include both climate variations and human activities.
Another pressure factor, which originates from both natural and human
causes, is fire. A natural cause of fires is lightening strikes. Fire
is useful in grassland areas because it prevents bushes from encroaching,
removes dry vegetation, and recycles nutrients. Farmers use it to clear
land for conversion to agriculture and to control pests. But too many
fires and extensive burning can degrade grasslands. About 500 million
hectares of tropical and subtropical savannas, woodlands, and open forest
are burned each year.
Overgrazing is also an important degrader of grassland condition, especially
when livestock numbers are high, animals are confined to small grazing
plots without rotation, vegetation is sparse, and soils are easily eroded.
And the amount of forage, or livestock food, a grassland can produce depends
in part on soil conditions. Indicators show that more than half of all
remaining grasslands have some degree of soil degradation. In many regions
overgrazing and drought pose a serious threat to the future of grasslands.
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Source: This profile is adapted from the companion book, World Resources 2000-2001.
For comprehensive data about the world's ecosystems, visit EarthTrends at http://www.earthtrends.wri.org/.
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| Grasslands | Freshwater
The Value of Ecosystems