Human activity affects rainforest ecosystems in many ways, some of which are negative and some of which are positive. One impact of human activity is the loss of nutrients from the soils of the rainforest. This occurs as tropical vegetation is interfered with or removed by deforestation, this leads to changes in nutrient availability and transfers. In the rainforest most of the nutrients are stored within the biomass and the ground litter reservoirs, the main transfers are between these two reservoirs. Dead and decaying matter decomposes rapidly and plant roots then take up nutrients.
Under human influence of for example a ‘slash and burn’ regime with a three year cropping limit and a long fallow period in between the nutrient levels in the litter and the biomass decrease and the nutrients in the soil increase. This is however counteracted by heavy rain which causes loss of nutrients through leaching, soil erosion and to the atmosphere. Soil fertility increases during periods of fallow should sufficient time be allowed. Rainforest ecosystems under permanent cultivation show depletion in nutrient stores in the biomass, litter and soils. Soil fertility therefore reduces rapidly. Areas that have been intensely cultivated in the past might never return to their former forest cover and are much more likely to be covered in heathlike vegetation.
Soil erosion is also an effect of human activity in rainforest areas. Soils of the tropical rainforest are ferralitic soils or latosoils. Once again it is deforestation that causes this problem, as under natural conditions, the tree canopy would provide an effective shield against heavy rainfall. Ground litter would usually absorb some of the falling rainfall therefore protecting the soil further. Tree roots and animal burrows also allow rainwater to percolate through the soil with the result that levels of soil erosion are low under the natural vegetation cover. Without this rapid removal of the topsoil occurs, leaving behind an impermeable laterite layer that hardens when exposed to air. Soil erosion also causes deep gullies to form, which cause problems for the construction of roads and buildings. The heavy machinery used for this may also compact the soil, reducing infiltration rates and possibly causing mudslides on steep slopes.
Silting and river flooding may also occur as soil that has been eroded from deforested areas is carried downstream, contaminating water supplies and increasing suspended sediment loads. River flooding however might occur after deforestation because a smaller amount of rainwater is lost via evaporation from the trees causing an increase in runoff. Infiltration is reduced through laterisation and compaction therefore large quantities of soil-laden water flow over the surface and directly into the river channels causing flash floods. Landslides may occur and agricultural land may be lost.
The rainforest may also undergo a loss of biodiversity. As rainforests are cut down, flooded or burnt many species are threatened. Rainforests contain 50-90% of the world’s species; Amazonia itself contains over a million with only about 40% identified. At the current rates of deforestation the planet is estimated to be losing between 20 and 75 species every day. If this continues we can expect 8% of existing species to be lost by 2015. This can have great impacts on medical research that uses tropical plants in the search for new drugs. During the late 1980s, the United States National Cancer Institute identified more than 2,000 tropical rainforest plants with the potential to fight cancer. With more and more of the rainforests being destroyed, the chances of finding new cured are severely reduced.
Human activity affects the indigenous population of the rainforest. Indigenous people are physically adapted to their environment to stop them from over-heating but they have no immunity to western illnesses such as flu and measles. Therefore since coming into contact with outsiders the populations of many rainforest tribes have rapidly decreased. It is estimated that there were more than five million Indians living in the Amazon rainforest in 1500. By 1900 this had fallen to about one million and recent estimates suggest that there are currently fewer than 200,000 left.
The population of the Waimiri-Atroan Indians tribe was 6000 in 1903; by 1973 this had fallen to 3500 and by 1986 there were only 374 people left. Most died from measles epidemics whilst others were hunted down and shot by gunmen hired by local landowners. Rainforest people are also threatened by dam construction and logging as tribes can be displaced. Commercial logging in Sarawak results in the loss of 2000 km2 of rainforest every year, however Malaysian government puts the needs of the logging companies before those of the tribe who face imprisonment if they interfere with logging activities.
Deforestation in the rainforest is a major cause of these problems as during the nineteenth century, exploitation of the Amazon was confined to rubber tapping; this peaked at the turn of the century. Agriculture began in the late nineteenth century and was based upon the native system of slash and burn. Settlers however soon found that crop yield deteriorated rapidly and so they begun clearing greater amounts of forest. Deforestation increased rapidly between Belem and Braganca where the building of a railway added to the deforestation problems by consuming land and fuel.
Plantations for rubber were successful but at the same time were hampered by soil erosion and weed invasion. The construction of new roads allowed for an increased population in previously inaccessible areas. The new capital city of Brasilia was started in 1960 when the first Transamazonia highway was completed. Tax incentives were offered to tempt settlers into the region. The purpose was to flood the Amazon with civilisation by attracting multinational companies to invest in the region and encourage people to move out of the overcrowded cities in the rainforest.
Since the 1960s, five main activities have contributed to the deforestation of the Amazon. Agricultural colonisation has taken place along major roads and designated agricultural growth poles. Rainforest has been cleared to produce commercial crops. The creation of pastures for cattle ranching helped by large subsidies has resulted in the clearing of the forest along highways and around cattle growth poles in eastern and south-eastern Para and northern Mato Grosso. Mining has taken place around several planned ago-mineral growth poles. Large hydroelectric schemes have resulted in flooding of over 4500km2 of Amazon rainforest. Major logging centres were also established in Amazonia as road networks opened up the forest.
However since 1988 international pressure was put on the Brazilian government to reduce the scale of deforestation. Tax credits on cleared land have ended as a result of this. In 1991 it was announced that the government would withhold subsidies for agricultural development including cattle ranching and any projects, which involved deforestation. Recent estimates suggest that the rates of deforestation in the Brazilian Amazon now lie between 1.7 and 3 million hectares a year.
Human impact on the rainforest is not always negative; conservation for example acts for the protection and possible enhancement of natural landscapes or environments for future use and concentrates on the sensible use of resources. At present there are 91 acres of areas designated for protection in the Amazonian region. These areas vary from several hundred to thousands of hectares with the greatest concentration of conservation areas occurring in the area centred on the Peru, Bolivia and Brazil borders.
As well as governments declaring parts of the forest as protected lands rainforest destruction can also be stopped by restricting the buying and selling of tropical woods like mahogany, ensuring that all cleared areas are replanted with trees, withdrawing exploration and mining licences from organisations working in protected areas, limiting tourism and developing Ecotourism, development of eco-forestry, encouraging sustainable fishing and providing legal and medical protection for Indian tribes at risk.
The Tambopata Candama Reserved Zone is a nature reserve in the Amazonian forests of Peru. In terms of biodiversity these are the richest forests in the world. In one small part of the TCRZ there are 587 species of bird, 1230 of butterfly and 150 different types of tree. The TCRZ was created in 1990 by ministerial decree. It included 1.479 million hectares and contains a mixture of sub-tropical forest, cloud forest and tropical savannah.
In the reserved zone, forest conservation is encouraged and local traditional lifestyles supported. Various health initiatives are working to enhance community life by supporting sustainable projects. There are two health centres involved in the training and support. Groups also carry out scientific research in the reserve supported by TreeS, the international voluntary organisation of the Tambopata Reserve Society. The area is however under threat from oil and gad exploration, jungle lodges, construction of highways and cattle ranching.
The Amazon rainforest is therefore impacted by human activity in both negative and positive ways in some cases for economic gain and in other cases for the protection and enhancement of the landscape for future generations to come. Problems arise when these views over a specific area are conflicting and it must be decided which is more worthy.