What in an pronounced alteration of the structure

What is a savanna biome? The savanna
biome (also known as a plain) is defined as grassland with some isolated trees
and shrubs. This biome is often found near forests or semi-desert regions.

Savannas are mostly located near the equator between the Tropic of Cancer and
the Tropic of Capricorn. The largest savanna is located in Africa, where nearly
half of the continent is covered with savanna grasslands. Other major savannas
are located in South America, parts of India and northern Australia. Savannas
cover about 20 percent of the earths land and 
possess a huge diversity  of
unique plants and wildlife. Did you know that savannas such as the Serengeti,
National Park in Tanzania are home to the largest animal populations on earth? Tropical
grassland animals (which do not all occur in the same area) include zebras,
giraffes, elephants, snakes, lions and leopards. The worlds greatest diversity
of hoofed mammals is found on the savannas of Africa.

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Savannas have a great economical
relevance. Thus, most agriculture of sub-Saharan Africa takes place in savanna
areas which support most of the continents cropland and pasture areas. The
significant wild animal diversity supports tourism as important source of
income of the local inhabitants revenue while the plants are important as food,
medical plants and construction material.

 

However, savannas are in danger due
to the human-induced climate change resulting from the greenhouse effect. This may
result in an pronounced alteration of the structure and function of savannas. Savannas
are expected to be strongly affected by climatic changes because they depend
heavily on rainfall quantity and seasonality (measure how long the dry season
is).

 

The expected climatic change will
influence different savannas in a various ways 
(1). There will be regions with more rainfall such as the Sahel region,
Chad or Central African Republic. In other Sahelian regions, such as Burkina
Faso, however, there will be less rainfall.

            Regions
with increased rainfall will be characterized by increased tree growth and
cover. A “CO2 fertilization effect”, caused by increasing atmospheric
carbon dioxide is considered to additionally enhance this tree growth (2). Large
parts of Africas savanna may, therefore, be forests by 2100. A switch from
Savanna to forest occurs once a critical threshold of CO2 concentration is
exceeded, yet each region has its own dynamics (3). Increased amounts of trees
and shrubs could threaten the entire savanna ecosystem, as these plants use
more water than grasses. The balance between tree cover and grassland is
crucial and it influences ecological systems (3).

            In
contrast, regions with less rainfall and longer dry seasons may be associated
with desertification. These changes are already being felt. Each year, over
46000 square kilometers of African savanna becomes desert.

 

This effects of  the expected climate change in the savannas add
to other severe problems associated with overgrazing and clearing of the land
for crops. Thus, about 16% of tropical grasslands have been converted for
agriculture or urban development. In tropical systems, CO2- fertilization,
fires, deforestations, and erosion are further contributing factors.

 

These climatic changes have crucial
effects. The balance between tree cover and grassland will affect survival of wildlife.

It is expected that the proportion of threatened mammal species may, according
to the Intergovernmental Panel in Climatic change, IPCC (2007) (4), increase to
between 10 and 40% between 2050 and 2080 due to the changing savanna and
grassland regimes in Africa. Observed population declines in three African
savanna hoofed species suggest that summer rainfall reductions could result in
their local extinction if climate change trends continue.

 

In summary, the climatic changes has
very dramatic effects in especially on savannas, although the mechanisms may
regionally differ, i.e., those associated with increased or reduced rainfalls.

It is, therefore important to take measures to reduce progression of those  changes changes.

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