by william ollar





Cause and effects of tropical deforestation




Introduction:

Tropical rainforests cover a large portion of the earth and they are home to a very diverse population. Many endangered species of animals and plants reside in the rainforest, also many medicines are dervied from the plants found only in the tropical rainforests. It is obvious that the destruction of the rainforests would be catastrophic to the global system, the impact of this destruction is not known. What is known is the rate of destruction, " every minute, global tropical rainforests are being destroyed at a rate of 150 acres per minute"( Sudzina 2002). How did tropical deforestation begin, what are the causes and the effects. By the end of my paper we will have a better understanding of the causes and the consequences of deforestation.
Throughout most of history, humans were hunter gatherers who hunted within forests. In most areas, such as the Amazon, the tropics, Central America, and the Caribbean, only after shortages of wood and other forest products occur are policies implemented to ensure forest resources are used in a sustainable manner. Deforestation probably started when humans first began farming, realizing that the soil in the tropics could be used to grow the plants that they needed. They no longer needed to move around as they followed the animals they were hunting. When the logging industry started up they realized that the tropics were ripe with possible profits. They got out of control at which point regulations were put in place to control the amount of lumber they were allowed to remove from the tropics and other areas.
There are many different causes of deforestation. The first one I will discuss is slash and burn agriculture. Slash and burn agriculture is where " the vegetation is cut and later it is burned to release the minerals into the soil. This is a common practice for farmers hoping to enrich the soil"( Sudzina 2002). Nutrients will be washed out of the soil every time it rains after some time the land will no longer support crops and the famers will leave. " After the land is abandoned, the rainforest will take approximately 50 years to grow back because the soil quality is so poor" (Sudzina 2002). The next cause of deforestation is logging, both selective logging and clear cut logging are highly destructive to rainforests. Selective logging is where " Only particular trees are chosen for logging and the ones around them are left standing. Although there is research indicating that when 3% of the trees were harvested, 49% were damaged" ( Sudzina 2002). It still takes 50 years or less for a section of rainforest to recover after selective logging, but it normally happens faster due to the fact that there are still trees around to spread seeds. The second and much worse form of logging is clear cut logging which is " when all of the trees are cut regardless of the species, leaving the ground bare. No tree trunks, vegetation or nutrients are left on the land and so scientists do not know how long it takes for the forest to grow back, except that it is longer than 50 years as of now" ( Sudzina 2002). There are regulations in place to control logging, but some companies ignore the regulations and harvest more than they are allowed to which can cause serious effects on our environment. Cattle pastures can also take more than fifty years for a rainforest to recover from. " Cattle grazing accounts for 72% of global deforestation. One reason for this huge amount is that the grass growing in the cleared forest is only good for an average of two years. Then a new plot is destroyed to provide a new grazing area. The Costa Rican rainforests have shown the repercussions of cattle grazing when it estimated in 1983 that 83% of its rainforests had been destroyed, mainly for meat production. ( Sudzina 2002) all these methods of deforestations lead to some very serious effects.
Deforestation can cause serious effects on the climate. As the rainforests are replace by pastures they cause changes in the climate " pastures have lower surface roughness length, higher stomatal resistance, a shallower and sparser root system, and a lower available storage capacity for soil moisture than tropical forests. The land surface and overlying air is warmer because of the reduced evapotranspiration and precipitation. All of these factors have led to a longer dry season".( Sudzina 2002) This will change the climate and eventually make it harder for the forest to replace itself. In the tropics, when land use changes it can cause the "atmospheric energy to change in deep convection. Deep tropical convection, fueled by heat and moisture through the release of latent energy, drives plumes deep into the troposphere and is the main source of precipitation in the tropics." (Synder 2010). As trees and other plants are removed it can cause changes to occur in the hydrological system. Trees allow raindrops to reach the ground at a slower speed. The roots hold the soil in place which allows for " low runoff rate of 25%, but after clearing, an average of 75% of the precipitation results in runoff. This runoff dramatically decreases infiltration that causes a decrease in the available soil-moisture and aquifer recharge." ( Sudzina 2002) Evaporation also leads to decreased moisture, " Two climatological methods have shown that 50% of the total precipitation, an unusually high amount, is recycled through the process of evapotranspiration in a short amount of time. Thus, without the vegetation, the region becomes much drier, supporting the theory that a climatic result of a longer dry season that will make the region uninhabitable for rainforests to reestablish themselves.(Sudzina 2002). Another thing that affects the climate due to deforestation is the release of green house gasses. Rainforests hold and cycle a large amount of carbon. " An undisturbed tropical rainforest is balanced, and part of this balance is cycling 3% of the atmospheric carbon, where there is no net gain of carbon or oxygen. The vegetation of a tropical rainforest contains 20-100 times more carbon than the agricultural lands that replace them. Tropical forests can hold as much as 600 metric tons of carbon per hectare when cropland can only hold about 5 tons. Therefore, when the deforestation occurs, the excess carbon is released into the atmosphere." ( Sudzina 2002) The rise in carbon in the atmosphere has been blamed on global warming. " In 1990, tropical deforestation was contributing 35% of the worldwide emissions of carbon(6). In addition to carbon, deforestation also contributes to the more radiative green house gases methane and nitrous oxide. Deforestation produces 38-42% of the global amount of methane, although only a small amount is released into the atmosphere compared to the amount of carbon dioxide during deforestation. The ratio of methane to carbon dioxide emitted in fires associated with deforestation is around 1%. Methane is generally two orders lower than carbon dioxide. The reason for its high production from deforestation is that it is indirectly produced by the cattle ranches and rice cultivation that replaces the tropical forests. ( Sudzina 2002). One of the main reasons rainforests are being cleared for cattle pastures is the growing need of meat by developed countries like the USA. " A majority of the cattle being grazed on the newly deforested area provides the meat for many of the major American fast food restaurants. It is estimated that the making of a McDonalds Quarter-Pounder destroys 55 square feet of rainforest. This plot of land contains on average 1 giant tree, 50 smaller trees, 20-30 different tree species, over 100 species of insects, as well as the birds, mammals, and reptiles." (Sudzina 2002)
the rainforests are a very important part of the environment, but they are being destroyed at an alarming rate. Which causes there to be less moisture available in the soil and more run off to occur. Also a large amount of greenhouse gasses are being released which is contributing to global warming. Also as land is turned into pastures it cause a longer dry season to occur. There are ways to stop this, we can try and deal with the effects of deforestation as they arise, or we can study the rainforests and learn as much as we can and see if there is a way to stop the changes in the climate and environment. We could also impose more regulations, but in my opinion they would just be ignored like a lot of the regulations that are in place at this time. Hopefully in the future there will still be rainforest to provide home to the many species of animals and plants that live there. Also for future generations to enjoy.

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References
1. Sudzina Chris; jrscience.com[internet]. 5/17/00 http://jrscience.wcp.muohio.edu/FieldCourses00/PapersCostaRicaArticles/Final.MethodsandEffectsof.html
2. Synder peter; American metterological society; 10/25/08