first appeared during the Eocene Era, and their success supported
the development of the communities of grazers that inhabit the
great grassy plains of our planet.
Grasses grow where
there is not enough moisture to support trees, where rainfall
is from 10-30 inches a year. Although coniferous forests
get similar amounts of rainfall, they are nearer the poles than
the grasslands are. Water evaporates more quickly when it is
warmer, so effectively the grasslands get less water for the
plants to use.
are perhaps 11,000 species of grasses, each one adapted to survive
under particular environmental conditions. Some kind of grass
can be found almost anywhere on land, and there are even grasses
that live in water. About a quarter of the vegetation on our
planet consists of grasses, some of them growing under very difficult
conditions. Antarctica has only two flowering plants, and one
of these is a grass.
Grasses have developed
unique characteristics to help them to survive. Drought can be
a problem in the grasslands. During dry periods grasses can become
dormant, leaving only dry stems and seed heads standing above
the roots. When rain falls, new shoots come up from the roots
again. Some grasses are annuals, and survive the winters as seeds:
other species are perennials, and sprout again each year from
a well-developed network of roots.
adaptive characteristic of grasses is that they grow up from
where the stems join the roots. Other plants grow from the tips
of shoots, twigs, and branches, but grasses grows from the bottom
up. This allows animals to eat grass without slowing its growth,
and people to mow lawns without killing the grass.
Grasses are wind pollinated
flowering plants. The tiny flowers form at the top of the stalks
where the wind can pick up and deliver the pollen. Later the
seed heads form at the top of the stalks. Grasses are monocotyledons,
so that when the seeds germinate each one sends up a single leaf.
There are grasslands
in many places in the world. The huge grasslands of this biome
are found in the interior of continents, on land that is gently
rolling or nearly flat. This type of terrain soaks up the rain
from summer thunder showers as it falls, so there are not many
rivers.The American prairies, the pampas of Argentina, the steppes
of Russia, the Serengeti in Africa -- all are homes to great
expanses of grass and distinctive communities of animals.
In America we use
the buffalo and the prairie dog as symbols of our grasslands.
The actual fauna is much more diverse, with antelopes, burrowing
mammals, snakes, and ground nesting birds. Predators range from
grizzly bears to foxes and include hawks and owls. Each grassland
has its own animals, and they tend to live in similar ecological
are subdivided into tall grass, medium grass, and short grass.
Grass heights may be 30 inces tall or taller, or less than a
foot in height. Shorter grass usually indicates that there is
less available moisture, but, in some environments such as mountain
tops, short grass may be adapting to a shorter growing
an important source of food for people as well as animals. Half
of all calories in the human diet come from grasses: wheat, rice
and maize (corn). These grains provide carbohydrates, which give
us the energy to move, work, and keep our bodies warm
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