Between 1990 and 2005, the planet lost 3% of its total forest cover, a net loss of 18 million acres (7.3 million hectares) of forest a year, or 50,000 acres (20,000 hectares) a dayóa loss that is all the more considerable because it takes into account the positive role played by plantations and natural regeneration. In fact, 32 million acres (13 million hectares) are deforested each year, an area equivalent to the surface area of Nicaragua or Greece. Between 2000 and 2005, fifty-seven countries recorded an increase of wooded areas, and eighty-three a decrease. Since 2000 the pace of deforestation has been accelerating in Southeast Asia, while the biggest reduction of forest was recorded in Africa, where 9% has been lost in fifteen years.
It is difficult to determine the primary cause of global deforestation: whether non-sustainable exploitation of wood resources or forest clearance for the benefit of animal rearing and agriculture. These two causes can be closely linked. Forests are also cleared in order to make way for mining activities and to build towns, roads, and dams. There are also indirect causes for deforestation, such as the absence of regulation and controls, the high demand of developed countries for forest or agricultural resources, and also the poverty of developing countries.
The consequences of the disappearance of trees are multiple. Forest soils become fragile and impoverished, especially in a tropical environment, and after a few years they may turn out to be agriculturally unproductive. The regeneration of the forest cover is then, at worst, compromised or, at best, will only occur over decades. Thewatercycle is also disturbed. In deforested regions, rivers experience more dramatic fluctuations in their water levels. Populations face catastrophic flooding and also episodes of more marked drought. Often, the absence of trees triggers various phenomena associated with erosion, the most spectacular being landslides. But, without doubt, the most alarming factor is the loss of biodiversity. Tropical forests are home to more than half of all terrestrial species. And it is estimated that one in ten plants contains an active substance potentially useful to medicine.