(Source: http://www.tutorvista.com/content/biology/biology-iv/ecosystem/)
1.4 Nutrient cycle
Nutrients cycle is the tight and rapid circulation of nutrients from the environment to organisms and back again to the environment. Nutrients are stored in the biomass, litter and soil. Figure 4 illustrates the flow of nutrients in the tropical rainforest ecosystem.
Figure 4.Process of nutrient cycling
(Source: http://onlinegeography.wikispaces.com/)
2. Ecological Importance of Vegetation
2.1 Atmospheric Function
It serves the purposes of balancing the atmospheric content between carbon dioxide and oxygen. At daytime, vegetation absorbs carbon dioxide, a major greenhouse gas warming the Earth, during photosynthesis. At night, it emits oxygen which is a necessity of all living things. This helps maintain the micro-climate.
2.2 Hydrospheric Function
Vegetation helps prevent excessive evaporation of water from the land surface and maintain the level of water table by infiltration. Hence, reduce the risk of flooding and drought.
2.3 Lithospheric Function
Apart from providing nutrients, vegetation also binds the soil to increase soil cohesiveness and provides shelters for land from erosive wind and water. This helps prevent soil erosion effectively.
2.4 Biospheric Function
It maintains the species diversity. A complex vegetation structure provides habitats for a lot of wildlife. At the same time, a large amount of primary producers serve as the food supply for animals. This helps sustaining the ecological balances in tropical rainforests.
3. Situation of Human Activities in Tropical Rainforests
3.1 General Phenomenon of Deforestation
Most countries in equatorial region are poor and less developed. They need capital for development and repaying foreign debts. Tropical rainforest provides great opportunities to human for economic purposes. As a result, large-scale of deforestation is carried out. From Table 1, the global rate of destruction can be up to around 3,500,000 hectare annually.
Table 1.Highest average annual deforestation of primary forests in 2000-2005
(Source: UNFAOGlobal Forest Resources Assessment 2005)
Heinrichs (1996) suggests that if the current rate of deforestation continues, the world's rainforests will vanish within 100 years. This will cause unknown effects on global climate and eliminate the majority of plant and animal on the planet.
The followings are the four common types of human activities causing deforestation in tropical rainforests.
3.2 Agriculture
3.2.1 Shifting Cultivation
Shifting Cultivation, also known as slash-and-burn, is a traditional farming method used by the native tribes. They choose a suitable site in the rainforests and then cut and burn the tress there. The ashes left make the soil fertile and crops can be planted in the cleared plot. After a few years of cultivation, the soil becomes poor and crop yield drops. They finally move to a new plot of land and repeat the farming cycle again.
3.2.1.1 Development of Shifting Cultivation
This farming method was considered sustainable in the past. Before 1975, the population of native people was small. The old plot of land can be left fallow for a sufficiently long period of time for the rainforest to recover. The ecosystem can then regain its equilibrium.
Yet, with a high rate of population increase in recent decades, more crops have to be grown on the same plot of land to support the huge population. Taking Kayapo people as an example, they are indigenous people living in Amazon Rainforest. Their population size rises from 4000 in 1995 to 8500 in 2010 (Asner 2006). The carrying capacity in tropical rainforests is low. Therefore, soil is depleted at a faster rate. This shortens the fallowing period and the farming cycle. Rainforests have less time for regeneration.
3.2.2 Plantations
Tropical rainforest is cleared for growing cash crops for export, including rubber, sugar cane, coffee, etc. Due to high level of urbanization, the world population and the living standard is both rising. Thus, the demand for tropical cash crops is increasing. This causes a rise in their prices and provides incentives for setting up more plantations. With the support of local government, huge tracts of tropical rainforest are being cut to make ways for plantations. This greatly accelerates the rate of deforestation. Figure 5 describes the palm oil production in Indonesia and Malaysia from 1964 to 2006. Both show a significant growth and this illustrates the rising importance of plantation to the countries' economies. But at the same time a greater destruction to the environment.
Figure 5. Annual palm oil production by Malaysia and Indonesia from 1964-2006
(Source: mongabay.com)
3.2.3 Cattle Ranching
A large area of rainforest is cut down to provide pastureland for cattle ranching. It can be regarded as the main source of soil deterioration (Sluyter 1996). Without vegetation cover, the pasture is not protected from heavy rain. Overgrazing occurs when excessive number of livestock is reared. This accelerates soil erosion and soil quality deteriorates. Cattle ranchers move to a new site and this causes a huge destruction to rainforest.
3.2.3.1 Reasons for rapid cattle ranching
The demand for beef is extremely high nowadays due to an improving world's living standard. This applies especially for Brazilian beef which are cheaper and safer (not infected by livestock diseases) in international markets.
Besides, local government often supports this activity. The environmental awareness in these countries is usually very low and they pay little attention on rainforest conservation. At the same time, they are in heavy debts so through the export of beef, national income and standard of living can be enhanced. It also helps repaying debts and stimulates its other economic activities.
Over-cultivation has destroyed the fragile ecosystem. This exacerbates environmental degradation and lowers agricultural productivity, thereby contributing further to poverty of developing countries.
3.3 Commercial Logging
There is a large variety of trees in tropical rainforests. Most of them are valuable hardwoods which are quality for construction purposes and furniture making. Therefore, human carry out commercial logging in two ways, clear-cutting and selective logging to obtain the resources.
3.3.1 Reasons for rapid commercial logging
Multinational timber companies play a major role in accelerating commercial logging. Companies include Rimbunan Hijau, WTK, and Prime Group carry out large-scale logging activities in Papua New Guinea as governments of less developed countries welcome foreign enterprises to exploit their forests. Granting rights to those companies for logging activities can obtain loyalties for repaying debts.
Technological development contributes to the rapid clearing of rainforest. Improved logging technologies in recent decades such as the use of bulldozer and electric chainsaw shorten the felling processes.
Poor management also accelerates the rate of commercial logging. Even though restrictions are set up for rainforest conservations, the control and supervision by the forest ministry is ineffective and unenforceable. This makes was for illegal logging.
3.4 Dam construction
In order to provide irrigation water and plentiful energy for industry, transport and domestic uses, hydroelectric power is generated in rainforest countries. Forests are cleared for building dams. For instance, the Itaipu Dam has been installedalong the boundaries of Brazil and Paraguay, clearing an area of 1350km2 of rainforest (Kirkland 2010).
3.5 Mining and oil extraction
Many rainforests are rich in mineral reserves including bauxite, coal and even gold. Butler (2010) stress that gold mining is highly related to the destruction of rainforest ecosystem. Cyanide, a highly toxic compound, is used to separate gold from sediment and rock. Mercury has to be separated from gold deposits. Accidental spills of cyanide or discharging of mercury can lead to serious pollution in the rainforest. Figure 6 illustrates that the gold mining situation in tropical rainforest area increasing drastically from 1960s to 2000s. This poses threats to the environment.
Figure 6.Trends in gold production in Ghana before the mineral sector reform (1958-
1986) and after the Mineral sector reform in 1986 (1987-2002)
(Source:Parks, P.J., 2007. Natural resource use conflict: gold mining intropical rainforest in Ghana. Department of Agricultural, Food and Resource Economics, Cook College,Rutgers University, New Brunswick, NJ.)
4. Impacts of deforestation on Tropical Rainforests
4.1 Hindering Ecological Function
4.1.1Atmoshpere
Green plants are a carbon sink (Varone 2006). As trees are mostly cleared by burning, a lot of carbon dioxide is released into the atmosphere. The decrease in number of trees also reduces the amount of carbon dioxide absorbed by plants during photosynthesis. Carbon dioxide is a kind of greenhouse gas which can trap heat. This intensifies the greenhouse effect and thereby global warming.
4.1.2 Hydrosphere
When deforestation is carried out, the land is no longer protected by vegetation. Rain falls directly on the ground and infiltration greatly reduces. Surface runoff will increase, raising the risk of flooding.
4.1.3 Lithosphere
Deforestation worsens the problem of leaching. The typical soil type found in rainforest is oxisol. Under the hot and wet climate, organic matters in oxisol decompose at a fast rate. Soluble minerals are easily leached from the soil by percolating rainwater. Insoluble elements include iron oxides will concentrate as a layer deep in the subsoil. As most minerals in the soil are washed away, the soil becomes infertile. (Asner 2006) After deforestation, the top soil is washed away so the layer of iron oxides is then exposed, forming an impermeable layer called laterite. The land surface will become barren and hinder forest regeneration. (Figure 7)
Figure 7. Process of Leaching
(Source:http://www.sln.org.uk/geography/schools/blythebridge/gcseecosystemtropicalrf.htm)
4.2 Biodiversity Loss
As large area of tropical rainforest is cleared, the habitat of plants and animals is destroyed. The risk of extinction of many species and the number of endangered species increases significantly. Therefore the global gene pool is likely to diminish and the global biodiversity will reduce in long terms speaking. The food webis being distorted as links in the ecosystem is broken, hinder the functioning of the entire ecosystem.
Malaysia is one of the rainforest countries which possesses species diversity(Ahmad 2008). Table 2 shows the biodiversity in Malaysia facing the threat of extinction.
Table 2: Biodiversity in Malaysia
(Source: Sani,S., 2008. The encyclopedia of Malaysia: Volume 1:The environment. Archipelago Press)
The impacts of human activities on tropical rainforest is far-reaching, thus, threatening the global environment.
All in all, tropical rainforest is the one of the most unique ecosystems in the planet and it is important to the balance of nature. By considering the above human destruction to this vital lifeline of the Earth, it is time for us to protect our valuable resource. On national level, government can restore and conserve the rainforest by setting up more nature reserve and encourage ecotourism. International organizations should convene conference for the topic of ecological conservation to transfer information and techniques among countries. On individual level, we should refuse buying products made from destroying forests and use more recycled products to reduce wastage. If all of us are determined to help, our collective actions will have a great impact to our planet.
(2,132 words)
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