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A savanna is a
rolling grassland scattered with shrubs and isolated trees,
which can be found between a tropical rainforest and desert
biome. Not enough rain falls on a savanna to support
forests. Savannas are also known as tropical grasslands.
They are found in a wide band on either side of the equator
on the edges of tropical rainforests. Savannas have warm
temperature year round. There are actually two very
different seasons in a savanna; a very long dry season
(winter), and a very wet season (summer). In the dry season
only an average of about 4 inches of rain falls. Between
December and February no rain will fall at all. Oddly
enough, it is actually a little cooler during this dry
season. But don't expect sweater weather; it is still around
70° F. In the summer there
is lots of rain. In Africa the monsoon rains begin in May.
An average of 15 to 25 inches of rain falls during this
time. It gets hot and very humid during the rainy season.
Every day the hot, humid air rises off the ground and
collides with cooler air above and turns into rain. In the
afternoons on the summer savanna the rains pour down for
hours. African savannas have large herds of grazing and
browsing hoofed animals. Each animal has a specialized
eating habit that reduces compitition for food. There are several
different types of savannas around the world. The savannas
we are most familiar with are the East African savannas
covered with acacia trees. The Serengeti Plains of Tanzania
are some of the most well known. Here animals like lions,
zebras, elephants, and giraffes and many types of
ungulates(animals with hooves) graze and hunt. Many large
grass-eating mammals (herbivores) can survive here because
they can move around and eat the plentiful grasses. There
are also lots of carnivores (meat eaters) who eat them in
turn. South America also
has savannas, but there are very few species that exist only
on this savanna. In Brazil, Colombia, and Venezuela,
savannas occupy some 2.5 million square kilometers, an area
about one-quarter the size of Canada. Animals from the
neighboring biomes kind of spill into this savanna. The
Llanos of the Orinoco basin of Venezuela and Columbia is
flooded annually by the Orinoco River. Plants have adapted
to growing for long periods in standing water. The capybara
and marsh deer have adapted themselves to a semi-aquatic
life. Brazil's cerrado is
an open woodland of short twisted trees. The diversity of
animals is very great here, with several plants and animals
that don't exist anywhere else on earth. There is also a
savanna in northern Australia. Eucalyptus trees take the
place of acacias in the Australian savanna. There are many
species of kangaroos in this savanna but not too much
diversity of different animals Plants of the
savannas are highly specialized to grow in this environment
of long periods of drought. They have long tap roots that
can reach the deep water table, thick bark to resist annual
fires, trunks that can store water, and leaves that drop of
during the winter to conserve water. The grasses have
adaptations that discourage animals from grazing on them;
some grasses are too sharp or bitter tasting for some
animals, but not others, to eat. The side benefit of this is
that every species of animal has something to eat. Different
species will also eat different parts of the grass. Many
grasses grow from the bottom up, so that the growth tissue
doesn't get damaged by grazers. Many plants of the savanna
also have storage organs like bulbs and corms for making it
though the dry season. Most of the animals
on the savanna have long legs or wings to be able to go on
long migrations. Many burrow under ground to avoid the heat
or raise their young. The savanna is a perfect place for
birds of prey like hawks and buzzards. The wide, open plain
provides them with a clear view of their prey, hot air
updrafts keep them soaring, and there is the occasional tree
to rest on or nest in. Animals don't sweat to lose body
heat, so they lose it through panting or through large areas
of exposed skin, or ears, like those of the
elephant. The savanna has a
large range of highly specialized plants and animals. They
all depend on the each other to keep the environment in
balance. There are over 40 different species of hoofed
mammals that live on the savannas of Africa. Up to 16
different species of browsers (those who eat leaves of
trees) and grazers can coexist in one area. They do this by
having their own food preferences, browsing/grazing at
different heights, time of day or year to use a given area,
and different places to go during the dry season. These different
herbivores provide a wide range of food for carnivores, like
lions, leopards, cheetahs, jackals and hyenas. Each species
has its own preference, making it possible to live side by
side and not be in competition for food. In many parts of the
savannas of Africa people have started using it to graze
their cattle and goats. They don't move around and soon the
grasses are completely eaten up. With no vegetation, the
savanna turns into a desert. Huge areas of savanna are lost
to the Sahara desert every year because of overgrazing and
farming.
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