The impact of human activity in tropical rainforests - examples from Madagascar.

by alexdarcy3gmailcom (student)

The impact of human activity in tropical rainforests

Impact of human activity: deforestation:

Destruction of the world’s tropical rainforests is a major environmental issue. Deforestation is the deliberate clearance of woodland by cutting, burning or the application of a defoliant, such as that used during the 1960s by American troops to clear the jungle in Vietnam.

In some developing countries and NICs, tropical rainforests, such as those in the Amazon basin in South America, and in Indonesia and Malaysia in the far east, are being destroyed at an alarming rate. There are claims that half of the world’s original rainforests have already been cleared, with an area the size of the UK being cleared every year. Climatic climax vegetation has been destroyed and this has resulted in both secondary succession and pagioclimax. The vegetation that eventually grows to replace the original rainforest tends to be smaller in height and less diverse, with a reduction in the overall biomass.

Causes of deforestation:

Demand for hardwood, such as teak, for building and furniture is increasing and many developing countries rely on export earnings from timber to help pay their debts and finance major development projects
Deforestation also occurs to provide land for rubber plantations, cattle ranches for beef farming, soya plantations, roads and railways
In the Brazilian rainforest, rivers have been dammed and large areas flooded to provide water for hydroelectric power stations- example of such a reservoir lies behind the Tucuruí dam on the Tocantins River in Amazonia.
Forest is also being cleared in Brazil for mining
There are vast resources of aluminium and iron ores in the ground beneath the rainforest and the Carajás mining project in Amazonia has resulted in the destruction of large areas of climax vegetation
Most countries with large areas of rainforest are still developing economically. During the 1960s and 70s, the population of southeast Asia and South America increased rapidly because birth rates exceeded death rates, and so population pressure led to increasing clearance of rainforest.
In Indonesia, the transmigration policy encouraged people to move from the overcrowded island of Java to less populated islands such as Sumatra, where rainforest was cleared away to make way for settlements and agriculture.

Impacts of deforestation:

Impacts can be physical, economic, social and cultural, and mainly occur on a local scale, but some impacts can be global
As habitats shrink, plant species become endangered and the food chain within the forest is disrupted. Some animal species, for example orang-utans and tigers are threatened by extinction
The vegetation protects the latosol soils from the regular heavy tropical downpours. Once the trees are removed, the topsoil is open to erosion and to leaching of nutrients and minerals. Runoff causes sediment to block river channels and increases flooding
The microclimate of the forest is disturbed ...

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Impacts of deforestation:

Impacts can be physical, economic, social and cultural, and mainly occur on a local scale, but some impacts can be global
As habitats shrink, plant species become endangered and the food chain within the forest is disrupted. Some animal species, for example orang-utans and tigers are threatened by extinction
The vegetation protects the latosol soils from the regular heavy tropical downpours. Once the trees are removed, the topsoil is open to erosion and to leaching of nutrients and minerals. Runoff causes sediment to block river channels and increases flooding
The microclimate of the forest is disturbed by deforestation- the daily water cycle of rapid evapotranspiration followed by afternoon precipitation cannot occur, and there is less cloud cover, so a greater temperature range.
Burning associated with forest clearance leads to local air pollution and contributes to climate change
Deforestation can have economic benefits in terms of income from farming, mining and exports of hardwood. However, the culture of indigenous people is destroyed and they may be forced to move from their land

ECOSYSTEMS AND BIODIVERSITY:

Deforestation in Madagascar:

Madagascar, a large island located off the east coast of Africa, is one of the world’s most threatened hot spots for terrestrial biodiversity and is a priority for conservation action. Much of Madagascar’s flora and fauna is endemic: 98% of land mammals and 68% of plants exist nowhere else.

After 1896, when Madagascar became a French colony, the Malagasy forests were rapidly depleted.
Localised logging for fuel wood and clearing for agriculture were partly to blame; however this was mostly small scale.
Since the 1950s, rates of deforestation have increased rapidly, although this is not unique to Madagascar

In 1985, it was estimated that only 34% of the original rainforest remained in Madagascar and that deforestation was most rapid in areas of low relief and high population density. Due to the extreme debt of the Malagasy government, the country has been exploiting wood resources to pay off money owed to MEDCs. 71% of the country’s 17.5 million people are estimated to be below the poverty line.

Ranomafana National Park:

Large area of over 400km2 of primary rainforest in the southeast of the island
Lies 90km west of the Indian Ocean on the east facing escarpment of Madagascar’s central high plateau
Climate is subtropical, with rainfall varying from 2300mm to 4000mm per year
Temperatures average 18-20oC, with an all year round growing season
Sometimes the wet season brings cyclones that can have a destructive impact on the trees, causing forest blow downs and flooding
Soils are mostly clay and oxisols developed from parent rock, with extremely low levels of nutrients
Nutrient cycle in a tropical rainforest is easily disrupted- once vegetation is removed, nutrients are quickly lost from the system by intense rainfall, creating infertile conditions
Biological richness of the park is extremely high- home to 12 lemur species and one third of Madagascar’s bird species
Park is divided into a core protected zone of 41,500 hectares, surrounded by a peripheral zone in which some exploitation of the forest is permitted
The peripheral zone contains more than 100 villages with over 25,000 residents, most of whom are subsistence farmers. The aim of the RNP is to:

Promote research on biodiversity
Share information with policy makers and scientists, both local and globally
Conduct long term monitoring and research

It is estimated that if the park had not been established, then there would have been little or no forest cover left by 2025. However, complaints have been made that some of the 18 national parks were set aside without the consent of local people.

Impacts of deforestation:

Effects on the hydrosphere include: increased runoff, increased sedimentation in dams and increased discharge which can lead to increased flood risk

Effects on the atmosphere include: less absorption of carbon dioxide, reduction in shading, which means more direct sunlight may reach the forest floor and increased evaporation

Effects on the biosphere include: loss of biomass, decrease in number and range of important habits, decrease in species and genetic diversity and rapid soil erosion, which leads to a loss of nutrients

Solving the deforestation problem: non-protectionist approaches:

The establishment of protectionist approaches to managing the problem may only be a partial solution. Other options include the following:

Debt swapping. This is scheme initiated in the USA whereby banks based in MEDCs agree to reduce or remove debts from and LEDC, by allowing their debts to be purchased at a fraction of their real value and then used to finance conservation projects
Promote changes in agriculture. Changes in the current methods of farming may help protect soils. Palm trees can be planted, which increase the fertility of the soil and act as an interception layer, thus reducing storm runoff. The replanting of vegetables and hardwoods will also help to improve soil condition.
Changes in harvesting methods. Selective logging, rather than clear felling, allows the forests to regenerate more naturally
Increase the number of small scale conservation projects. More locally based conservation schemes may be possible, given adequate funding from foreign organisations e.g. WWF