school energy&environment

Forest and deforestation

According to FAO the definition of deforestation is closely related to the definition of forest. Infact, a forest is determined by the presence of trees and absence of forms of use which prevail in territories different from forests. FAO believes a “forest” is a part of land superior to 0,5 hectares, characterised by the presence of trees with a minimum 10% cover and a potential in situ height of at least 5 metres. A forest, therefore, doesn’t include all those lands which, although included in the definition above, are employed mainly for agricultural or urban use. Deforestation is defined as the conversion of a forest to another form of use of the territory for example for agricultural, cattle breeding, extraction, building or infrastructural purposes) or the reduction in the long term of forest cover below a 10% limit (FAO, 2001).
Deforestation doesn’t occur in forests if timber is extracted for cultivation treatments, for construction work or combustibles and if vegetation is capable of spontaneous renewal or thanks to forestry actions. On the contrary, therefore, deforestation occurs when the impact of biotic or abiotic disturbances doesn’t allow plant cover above 10% of a given area. Variations within forest cateogories, for example, as the transition from closed to open forest, are defined “forest degradations” even if they cause negative impacts on soil and land. In 2005, global forest extension amounted to about 3,952 million hectares (MHA), which is about 30% of land surface (FAO, 2006). 38,4% of global forests, equivalent to 1,338 million hectares, are defined by FAO as “primary forests”, which means forests of native species, in which ecological processes aren’t disturbed by human action. 59,8% of primary forests, about 2,000 million hectares, are represented by modified natural forests formed by native species generated by spontaneous renewal and where interference in ecological cycles are clearly related to the presence of mankind. Plantations are defined as forests with introduced species or, in some cases, native species planted or sown (3,8% of total forest cover, about 140 MHA). 78% of plantations is used for timber and fiber production, 22% for protective functions.
Deforestation constitutes a serious threat to survival of forests as, apart from tree extraction, it implies road construction and immigration of populations in deforested areas. The proportions of this environmental disaster are really impressive and the phenomenon has reached its most dramatic aspects in Africa. In the last thirty years, Africa has lost two thirds of its tropical forest and centuries-old forests by now are reduced to 8% of their original surface. In the Congo Basin, 85% of forests have been lost and the remaining 15% is now threatened by the logging industry. From 2000-2005, 7,3 million hectares have been lost every year (as a median annual difference beween 12,9 million hectares of deforestation and 5,6 million hectares of afforestation and reforestation) and an annual deforestation rate around 0,18%.