Transcript Document 7486486

Aims and objectives
• 1. What is deforestation?
• 2. Why have tropical rainforest been
cleared?
• 3. What are the impacts of deforestation?
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Where the forests are
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• Deforestation is cutting down tress – not just
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cutting down forests – as we saw last week
cutting down trees in the savannah is called that
too – even though the savannah can hardly be
called a forest.
Many primary forests in temperate countries
have almost disappeared after centuries of
logging or land clearance for farming, industry
and housing. But it is relatively recently that
large scale deforestation has taken place in the
tropical forests.
Meanwhile there are some temperate areas
where reforestation is taking place.
It speed has raised alarm with the scientists
and conservationists. What are they concerned
about?
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What are the scientists and
conservationists concerned about?
• Biodiversity is a major concern. Rainforest
are one of the most biologically diverse
regions of the world.
• Over a million species of plants and animals
are known to live in the forests and
millions more are not classified.
• The unique environment of the rainforest
allows for such biodiversity to exist.
• What is most of it cut down for?
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What are causes of deforestation in
tropical rain forests?
• Logging; Farming; Road building; Mining;
HEP schemes
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What do the governments think about
it?
• Some of the logging is illegal
• But in many case the governments encourage it.
• Often these are LEDCs with few ways of raising
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money
So the temptation to pay off debts and increase
the standard of living of their people is a hard
one to pass up
What do they gain from allowing deforestation?
 Revenue from timber, drugs (legal ones) and minerals –
and more recently exports of animal feed (soya) and
biofuels (palm oil)
 Land to house and feed their increasing population
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So what are the main impacts of
increased deforestation?
• The impact of deforestation on a large
scale can be divided in two
• Local Impacts are those that affect the
immediate area from where the trees are
being removed.
• Worldwide/International Impacts are
those aspects which affect everyone
everywhere.
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What are the local impacts of increased
deforestation?
• Climate Change
• When an area of rainforest is either cut down or destroyed, there
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are various climate changes that happen as a result. The following is
a list of the various climate changes with a brief description of why
they come about.
Desiccation of previously moist forest soil
What happens is because of the exposure to the sun, the soil gets
baked and the lack of canopy leaves nothing to prevent the moisture
from quickly evaporating into the atmosphere. Thus, previously moist
soil becomes dry and cracked.
Dramatic Increase in Temperature Extremes
Trees provide shade and the shaded area has a moderated
temperature. With shade, the temperature may be 37 degrees
Centigrade during the day and 16 degrees at night. With out the
shade, temperatures would be much colder during the night and
around 54 degrees during the day.
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What are the local impacts of increased
deforestation?
• Moist Humid Region Changes to Desert
• This is related to the desiccation of previously moist
forest soil. Primarily because of the lack of moisture and
the inability to keep moisture, soil that is exposed to the
sun will dry and turn into desert sand. Even before that
happens, when the soil becomes dry, dust storms become
more frequent. At that point, the soil becomes useless.
• Soil Erosion
• Deforestation contributes to run-off of rainfall and
intensified soil erosion. Bare ground, with little added
humus, increase the rate of sheet and gulley erosion.
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What are the local impacts of increased
deforestation?
• Changes in rainfall pattern
• The daily rainfall common in many parts of tropical
rainfall is called convection rainfall.
• Heavy rainfall in these areas occurs frequently in the
afternoon. Why?
• When it rains, the trees intercept much of the water,
slowing its rate of descent, allowing much of it to
percolate into the soil as the ground is shaded and so
much cooler than the air above. Much of the water that
has percolated the soil will be taken in by the roots of
trees and shrubs, which will transpire it into the
atmosphere in first part of the day when the sky is clear
and so the temperature rises. This warm moist air rises
in the atmosphere and eventually cools and condenses
into clouds in time for the next teatime downpour
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Every
morning
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Every
Afternoon
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About 4 o’clock
nearly every day
animated version of this is on http://ysgolrhyngrwyd.wikispaces.com/Unit+2+Environmental+conditions
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So what happens when the trees are cut
down?
• The shrinking forest cover that there are no longer
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trees to intercept, retain and transpire precipitation.
The deforested areas become sources of surface water
runoff, which moves much faster than subsurface flows
and can cause flash flooding and more localized floods
than would occur with the forest cover.
With decreased evapotranspiration, atmospheric
moisture is reduced the regular rainfall is reduced.
According to one preliminary study, in deforested north
and northwest China, the average annual precipitation
decreased by one third between the 1950s and the
1980s.
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What are the international impacts of
increased deforestation?
• Less Carbon Dioxide and Nitrogen Exchange
• The rainforests are important in the carbon
dioxide exchange process. They are second only
to oceans as the most important "sink" for
atmospheric carbon dioxide. Deforestation may
account for as much as 10% of current
greenhouse gas emissions. Greenhouse gases are
gases in the atmosphere that literally trap heat.
There is a theory that as more greenhouse
gasses are released into the atmosphere, more
heat gets trapped. Thus, there is a global
warming trend in which the average temperature
becomes progressively higher.
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A summary
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So what are the main impacts of
increased deforestation?
• Other Effects
• There many rewards such as clean air and
clean water, perhaps the two most
important, that forests provide.
• Rainforests also provide many aesthetic,
recreational and cultural rewards.
• If the rainforests are destroyed, then
these rewards disappear. This has major
social repercussions for the entire world
which will be gone into later.
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Medicines and Rainforests
• Tropical rainforests, which account for only seven
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percent of the world’s total land mass, harbour as much
as half of all known varieties of plants. Experts say that
just a four-square-mile area of rainforest may contain as
many as 1,500 different types of flowering plants and
750 species of trees, all which have evolved specialized
survival mechanisms over the millennia that mankind is
just starting to learn how to appropriate for its own
purposes.
Rainforests are a Rich Source of Medicines
Scattered pockets of native peoples around the world
have known about the healing properties of rainforest
plants for centuries and perhaps longer. But only since
World War II has the modern world begun to take
notice, and scores of drug companies today work in
tandem with conservationists, native groups and various
governments to find, catalogue and synthesize rainforest
plants for their medicinal value.
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Medicines and Rainforests
• Rainforest Plants Produce Life-saving Medicines
Some 120 prescription drugs sold worldwide today are
derived directly from rainforest plants. And according to
the U.S. National Cancer Institute, more than two-thirds
of all medicines found to have cancer-fighting properties
come from rainforest plants. Examples abound.
Ingredients obtained and synthesized from a nowextinct periwinkle plant found only in Madagascar (until
deforestation wiped it out) have increased the chances
of survival for children with leukemia from 20 percent to
80 percent.
• Some of the compounds in rainforest plants are also used
to treat malaria, heart disease, bronchitis, hypertension,
rheumatism, diabetes, muscle tension, arthritis,
glaucoma, dysentery and tuberculosis, among other
health problems. And many commercially available
anesthetics, enzymes, hormones, laxatives, cough
mixtures, antibiotics and antiseptics are also derived
from rainforest plants and herbs.
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Medicines and Rainforests
• The Untapped Potential of Rainforest Medicines
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Despite these success stories, less than one percent of
the plants in the world’s tropical rainforests have even
been tested for their medicinal properties.
Environmentalists and health care advocates alike are
keen to protect the world’s remaining rainforests as
storehouses for the medicines of the future.
The Challenge of Preserving Valuable Rainforests
But saving tropical rainforests is no easy task, as
poverty-stricken native people try to eke out a living off
the lands and many governments throughout the world’s
equatorial regions, out of economic desperation as well as
greed, allow destructive cattle ranching, farming and
logging. As rainforest turns to farm, ranch and clear-cut,
some 137 rainforest-dwelling species—plants and animals
alike—go extinct every single day, according to noted
Harvard biologist Edward O. Wilson. Conservationists
worry that as rainforest species disappear, so will many
possible cures for life-threatening diseases.
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Homework
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You have met the issues.
Our Case study will be the Amazon.
Research these questions
Qu 1: What are the main causes of deforestation
in the Amazon? (figures and/or graphs if you
can)
Qu 2: What are the main impacts of
deforestation in the Amazon?
Next week, we will look at what can be done
about all this. How the rainforest can be
managed, how organisations like REDD and the
Rainforest Alliance try to cope and individual
efforts to make the
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