animals and people. For instance, the tallgrass prairie of the eastern Great Plains
has all but disappeared. Agriculture is prolific in the more precipitation-rich grass-
lands with all the major grain crops having originated in grasslands and being var-
iants of grasses. These crops include millet, sorghum, corn, rice, and rye. When
considering the human influence, it is apparent that up to a third of the species of
grasses in regions such as the Great Plains are not native to the region.
In general, there is lesser diversity of plant and animal species in grasslands
compared to adjacent forests. However, this cannot be taken to mean a paucity
of life. All sorts of bacteria, fungi, insects, and earthworms are at home in grass-
land soils. Moreover, plentiful large herbivores are one signature of native grass-
land conditions. In North America, the bison once populated the Great Plains in
untold millions. In today’s African savanna, elephants, zebra, and wildebeests
are still largely present but in declining numbers. The herbivores may, in fact, help
keep grasses dominant in some places as herbivores are attracted to competing
plant types such as young trees and bushes.
Grassland dominates in places where moisture is precious. A complete grass
cover is very conservative of precipitation because of the slowing of surface runoff
to the encouragement of moisture infiltration into the soil. Closely spaced root
system mats help hold soil in place. AGreat Plains thunderstorm dropping
2.5 cm (1 in) of precipitation may well not generate any significant runoff into
streams. The increased infiltration leads to moist soil profiles under grasslands.
Complex root systems greatly increase the length of storage and percentage uptake
of soil moisture. So too is the leaching of soil nutrients slowed. This means that the
mid-latitude grasslands of the world provide some of the most nutrient-rich soils
when they are plowed for agriculture. Unfortunately, this is tempered by the fact
that the soils dry out and are susceptible to wind erosion once the grass cover
has been removed.
Of great importance to grasslands is the presence of fire. In dry seasons and
droughts the aboveground portions of grasses brown out, allowing lightning-
caused or human-caused fires to spread effectively, sometimes over millions of
hectares. Fire represents a sudden change in the mass/energy pathways in grass-
lands but it does not represent the end of life. Fire releases plentiful nutrients into
the top of the soil and the still-living underground portions of grasses are able to
poke above the surface to tap this natural fertilizer. Additionally, fire kills trees
and bushes helping grasses to dominate.
Native Americans were successful users of North America’s grasslands for
thousands of years before European contact. Yet, as the United States enlarged to
fulfill its “Manifest Destiny” during the 1800s, settlers neglected the Great Plains
in search of opportunities on the Pacific Coast. The grasslands were viewed as so
desolate compared to the woodlands ofthe eastern United States that the area
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