IV. Deforestation

 

Deforestation, or the clearing of trees, is a problem that affects the entire Amazon Rainforest ecosystem. Studies have attempted to model the effects of deforestation, yielding horrific predictions for the future of the Amazon Basin rainforest, assuming that the current pattern of deforestation continues unabated. To examine the effects of deforestation more closely, one 1990-1993 study replaced tropical forest and savannah lands with pastures in South America, north of 30°S. The most prominent affects on the water ecosystem were as follows:


Deforestation caused an increase in erosion and flooding.  Because tree root systems hold the soil together, the removal of those roots leads to an increase in the rates of flooding and erosion.  The removal of trees also means that less water will absorbed during the rainy season.  The rainy season therefore, can have devastating effects as heavy rains will be able to wash away vital, nutrient-rich topsoil.  This in turn leads to decreased biodiversity and species richness.


The method of slash and burn deforestation has a strong impact on the carbon cycle.  On average, the burning of one acre of tropical rainforest releases 180 metric tons of carbon.  In the atmosphere this carbon bonds with oxygen to form CO2. 

 

The methane cycle is also affected by deforestation.  Methane is created by floating meadows[1] and flooded forest, both of which are encouraged by deforestation.  Researcher Laura Hess describes the role of floating meadows in the methane cycle:  "Floating meadows are very productive, floating masses of grass. The[ir] stems elongate as the water rises and a canopy develops at the top of the water. Grasses can reach several meters in length and float at the top of the water. As water levels recede, the stems begin to decay. This causes a bubbling of methane and high methane emissions"  (Hauser, 2002). 
Deforestation can also cause increased methane production as a result of increased flooding, and therefore wetland expansion.  Methane in these wetland areas is produced as the water in these areas cuts off the oxygen supply to the soil.   This results in anaerobic fermentation, a byproduct of which is methane.

 

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[1] Grass colonies in the water that form large clumps, flood plants called macrophytes.