What are the effects of Deforestation?

Deforestation also has an effect on the hydrological (water) cycle. The forest itself slows down the rate at which rainfall hits the soil, and the roots of trees create conduits in the soil which help water absorption. The plants also transport water from the soil to the atmosphere via evapotranspiration. Indeed, evaporation from soil alone produces less water in the atmosphere than transpiration from trees, so the atmosphere may become drier as a result of deforestation. Finally, leaf fall and organic residue improve the capacity of the soil to store water and support new plant life. In the case of non-deciduous forests, the soils are often of a poor quality and pine needles in particular can contain toxic compounds, preventing other plant germination. In areas of high rainfall, deforestation can often lead to flooding and mudslides. Also, deforestation increases the rate of soil erosion, as the root system of plants helps bind the soil together and prevent it being washed away by heavy rains.

Deforestation can have global, as well as local affects. This is particularly true as a result of a loss of carbon storage capacity within the plant biomass of the forest, of the major greenhouse gas carbon dioxide. It has been estimated that 15% of the carbon dioxide released into the atmosphere in the 1980s can be attributed to the destruction of tropical forests alone. The sheer biomass of plant life in a forest allows large quantities of CO2 to be absorbed for photosynthesis, reducing the amount of CO2 in the atmosphere, which contributes to global warming. Effectively, wood is a carbon sink, which keeps carbon out of circulation for several centuries. When a forest is destroyed, not only is CO2 less absorbed, but the burning or decay of the wood releases all the carbon tied up in it. Only forests and coral reefs are capably of providing carbon sinks. The reduction in photosynthesis also leads to less oxygen in the atmosphere, vital for aerobic respiration of many other species.

Deforestation also has an effect on the nitrogen cycle. When the forest is first cut down, organic matter in the soil and decaying or burning trees ensures a relatively high level of nitrogen in the soil. However, this is short lived, because no fresh organic material is being added to the soil and saprobiants cannot decompose, and hence the levels of nitrates in the soil are rapidly depleted. Also, there are no nitrogen fixing plants to return nitrate to the soil. Therefore, eventually farmers will need to add nitrogen fertilisers to the soil, which contributes to the overall imbalance in the nitrogen cycle, and may cause eutrophication.

Today, biodiversity loss and global warming have become so important that they have both been addressed by international treaties. These include the 1992 Convention on Biological Diversity and the Framework Convention on Climate Change. There are a number of alternatives to deforestation. A balance must be struck between the economic needs of the population where the forests are located, the need for profits by Western logging companies, and the need to conserve or renew these resources. Where deforestation occurs in order to use the wood for timber, particularly in coniferous forests, a planned regime of replanting can be implemented in order to give a sustainable resource, for timber building products and wood pulp used for paper making. The same is true of deciduous hardwoods, although the timescales are much longer. In China, for example, the government has required every citizen between the ages of 11 and 60 to plant 3-5 trees per year and it claims that at least 1000 million trees have been planted in China every year, since 1982. Additional, consumer pressure can play a part - refusing to import rare hardwoods. For example in 1992, Austria introduced the 'Tropical Timber Labelling Act', the first demand-side attempt to educate consumers. Charities have been set up (such as the Arbor Day Foundation Rainforest Rescue Program) which uses donated money to buy up and preserve rainforest land, before the lumber companies can buy it. In the 1990s, there have increasing pressures on sustainability certification - with consumers only buying wood products where the producer is able to verify that reforestation is taking place. Many products today made of wood are labelled to show that they come from sustainable resources. Additionally, recycling paper reduces the number of trees cut down, and other dried plant products can be burnt instead of wood to supply heat energy.

In many cases however, the land is cleared for farming, and this has happened in many Western countries, including Britain over the centuries. New methods are being developed to farm more crops on less farmland (increasing yield per acre). Examples include high yield genetically engineered crops and the use of greenhouses. Also, farmers are being encouraged to return to the old crop rotation system of cyclical agriculture, where grass is allowed to grow on the resting farmland, allowing animals to graze and return nutrients to the soil. Using farmland for grazing also reduces the amount of forest cut down. In some areas, planting of crops and grazing of animals within the forest land itself is being used successfully (agroforestry). However, the effect of all of these measures is relatively small in comparison with the potential for profits from the mining of forests. It is mainly in the developed world where reforestation to produce sustainable resources is most widespread.

Bibliography:

http://en.wikipedia.org/wiki/deforestation

http://www.globalchange.umich.edu/globalchange1/current/lectures/kling/water_nitro/water_and_nitrogen_cycles.htm

http://www.usra.edu/esse/essmp/essmpbiogeo.html

http://future500.org/articles/3/

http://www.rcfa-cfan.org/english/issues.12-7.html