Tropical Rainforest - weather and climate

TROPICAL RAINFOREST Weather & Climate

Case Study of

People’s interference in a natural ecosystem
How an ecosystem / climate can be changed by people

Where is the rainforest ?

Generally between Tropics of Cancer & Capricorn around Equator, 23 ½ degrees north and south of the equator. Rainforest describes vegetation which is dense and lush growing in this hot wet zone. Rainforests grow in conditions with over 2,000 mm of rain and temps are above 26 degrees Celsius all year round.

Rainforests cover 6 million square kms, 7% of the earth’s surface. Approx. 60% of the world’s rainforests are found in Brazil.

What is the rainforest like ?

Hot conditions with tropical storms late morning to early afternoon as heat builds up. Humid conditions encourage great bio – diversity. Very dense vegetation. Scientists estimate that…..

Brazil’s rainforest is home to at least half the world’s bird population.
6 out of 10 living species in the world are to be found in the tropical rainforest.
Rainforests have been the source for medicinal plants which are known cures for e.g leukaemia and are used in manufacture of contraceptive pills.

Emergent layer – single tall trees which fight above the canopy to get sunlight.

Forest floor dark – very little sunlight pierces layers of vegetation.

Trees have shallow roots remaining where nutrients are.

Contrary to popular belief soils are poor – almost all nutrients are held in trees because the vegetation growth is so strong and the nutrients are needed.

Complex linking of precipitation, interception, evaporation, evapotranspiration.

Plants use sunlight to photosynthesise – CO 2 exchange hence term “lungs of the world”

Uses of the forest

Brazil’s economic pressures

In the 1970's five main pressures created the debts:

Oil prices rose (doubled then quadrupled by 1979) so Brazils import bill increased as it tried to fuel growing industry.
Oil rich countries had money to lend – Brazil borrowed from them and World Bank etc…
Export profits have had to be used to pay interest on international debts (from loans)
Prices for Brazil's exports fell on the world market (coffee, other food items).
The International Monetary Fund has pressured Brazil to ...

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Uses of the forest

Brazil’s economic pressures

In the 1970's five main pressures created the debts:

Oil prices rose (doubled then quadrupled by 1979) so Brazils import bill increased as it tried to fuel growing industry.
Oil rich countries had money to lend – Brazil borrowed from them and World Bank etc…
Export profits have had to be used to pay interest on international debts (from loans)
Prices for Brazil's exports fell on the world market (coffee, other food items).
The International Monetary Fund has pressured Brazil to change the economy – gave government targets to reduce government spending and borrowing (called Structural Adjustment Policy)

Pressure: debt repayment forced exploitation of natural resources:

The rainforest, Fast flowing rivers, Mineral wealth beneath the surface e.g gold, iron, bauxite, copper, manganese, Land available for creating estate farming cash crops

What effects of clearance ?

Interference in the hydrological cycle

Winds off the Atlantic blow east. These carry huge amounts of water, evaporated off the sea. The hot temperatures result in massive evaporation and cloud formation. As the winds blow across the land (over the rainforest), the rain falls. Trees intercept and absorb almost all the rainwater hence the dense vegetation. Trees use water and nutrients in the water droplets to grow. Very little of the water and nutrients are infiltrated into the lower layers of soil and rock.

Most water is evapotranspirated back to the atmosphere to form clouds which are blown inland by the same weather systems. The cycle is in balance.

Scientists fear that clearance of large areas will interrupt the cycle as clouds move inland. This is because there would be areas with no trees. Here, in these areas, more water would be infiltrated and lost to the groundwater system. Some water is likely to run off along the surface and could well increase soil erosion by rainsplash and rainwash processes. It would not be taken up by vegetation and evapotranspirated back to the atmosphere to form clouds. If the clouds did not form or were smaller, as the air is blown inland further, it is drier and there is less rainfall from lighter or non existent clouds. It is freared that this climatic change could mean a reduction in the rainforest further inland (too dry for dense lush vegetation) and a change in farming in the foothills of the Andes as a drier climate would restrict or change the suitability of crops.

Interference in the nutrient cycle

Common misconception that rainforest soils are fertile. They are for a short period in the cycle. Nutrients are immediately taken up via tree roots – hence lush growth of vegetation. If trees are cleared no leaves fall to the ground and soil is even poorer. Without tree roots to bind soil together, more soil is eroded and lost to the rivers. This extra sediment can block dams and can fill the river channel, causing the river to overflow and flood.

Effects on people

Tribal groups have lost land and have been marginalised. Belief by many groups that no one can own the forest, it is only theirs to look after for future generations. Some campaign groups have been attacked and leaders such as Chico Mendes murdered.

Greenhouse Effect

Amazon Rainforest often described as the “lungs of the world”. Scientists divided about the extent of this. Trees absorb a great amount of CO 2 from atmosphere, converting it to Oxygen. If trees reduced and the process of converting to Oxygen is reduced, there would be increased CO 2 in the atmosphere. This is linked to the Greenhouse Effect. By changing the amount of CO 2 the earth’s temperature would increase, the polar ice caps would melt and a rising of sea levels would follow, so the argument goes. It is also argued that increasing burning of the forests and industrial developments polluting the atmosphere in the forest area is adding to the effect.

NORMAL CO2

Incoming solar energy heats earth’s surface. The heat given off heats the atmosphere including CO2. Energy is reflected by earth as long wave energy.

INCREASED CO2

Earths surface is heated by incoming energy as normal. More reflected energy is absorbed due to increased CO2. Atmosphere warms up – “greenhouse effect”. Less energy is reflected by the earth.

Strategies for future

Action of pressure groups who campaign to raise awareness and educate all countries of the effects of courses of action.
Boycotting – timber users are encouraged not to buy from non – sustainable sources. Effectively this means only buying from those companies with certificates to prove they ruse re-afforestation schemes
Buying tracts of forest – some western charities encourage this to protect areas. Othere express disapproval of suggesting a prson can own rainforest land (clash with Native Indian belief that no one owns the land)
Encouraging non invasive organisations which use but do not destroy such as Eco tourism and medical research on species for Pharmaceutical industries. This would protect areas and prevent loss of species such as Madagascar Periwinkle which has been destroyed.
Encouraging controlled “wealth creating projects” such as “responsible mining” in selected areas. Targets a major income making industry so that damage is minimised for maximum gain.
Encouraging the worldwide use of softwoods which can grow more quickly – some pine trees mature in 20 years whereas a tropical hardwood tree may take 200 years.
Write off Brazil’s debt so that there is a reduction of the pressure to pay off loans. Some argue that Brazil has paid off the debt many times over through excessively high interest rates.
Timber Tax – on all timber cut from tropical sources. The tax would be used for re-afforestation schemes. Quotas on the number of trees which can be removed in particular areas.
Selective ring forestry – small scale clearance allowed (e.g.in rings so that space left is easily recolonised by the same species and trees invade again).
Creation of world rainforest parks / international biome reserves where no one country or company can operate without international agreement. An example is Korup rainforest in Cameroon.