Deforestation

One of the most notable processes by which humankind has affected the Earth's surface is via the conversion of forested land for agriculture, logging, and urbanization, that is, deforestation. Up through the latter decades of the 20th century, deforestation had accelerated and come to be almost totally concentrated in the tropics, almost [Page 696]wholly within developing countries. In the 1990s, the extent of old-growth forests was approximately one fifth of their original cover.

Estimates of land use change over the 20th century (the lion's share of which was concentrated in its last four decades) are crude, but research suggests that though Asia and Africa had a slightly greater percentage of their forests cleared (34% to 38%) compared with Latin America (approximately 28%), a far greater absolute amount was cleared in Latin America due to the vastness of the Amazon basin. A continuation of those rates would mean the end of tropical forests within 50 years and therefore the elimination of an area prized as a repository of biodiversity.

More recent estimates of global deforestation rates reveal that while the conversion of forest to agricultural land continues at the alarming rate of roughly 13 million ha/yr. (hectares per year), countervailing forces of afforestation (the conversion of open land into forest) via planting and natural expansion have significantly reduced the net loss of forested area. From 2000 to 2005, there was an estimated net decrease of 7.3 million ha/yr., a rate substantially lower than the average 8.9 million ha decrease per year between 1990 and 2000. During the 2000 to 2005 period, while the largest net forest losses occurred in Africa and South America, net forest loss also took place in Oceania and North and Central America. During the same period, Asia reported a net gain, primarily because of reported afforestation in China, despite the fact that Indonesia had one of the world's highest forest-clearing rates, though exact rates are contentious. Of all forested areas, primary forest constitutes 36%. Each year 6 million ha of primary forest are lost or modified, continuing trends reported in the 1990s. Although the trend in primary forest was toward a net loss, a few European countries and Japan reported gains in primary forest.

Forest-clearing “hotspots” in the humid tropical forest biome are revealed by the fact that 55% of the clearing occurs in 6% of the tropical biome's total area and is largely confined to the current agro-industrial clearing centers of South America and insular southeast Asia. The next level of intensity of clearing, constituting 40% of the clearing within the biome, is dispersed over 44% of the land area. The remaining 5% of clearing takes place within the predominately intact forest, which makes up 35% of the biome area, and within the 15% of the biome area that had already been substantially deforested prior to 2000. In this period, Brazil and Indonesia stand out as centers of humid tropical forest loss, with Brazil constituting 47.8% of all clearing and Indonesia another 12.8%. Other Latin America hotspots include Northern Guatemala, Eastern Bolivia, and Eastern Paraguay, with the Asian countries of Malaysia and Cambodia, particularly along the Thai border, having exceptional clearing rates. Africa's humid tropical forest loss is primarily through low-intensity selective logging, without the agro-industrial-scale clearing seen elsewhere. The loss of humid tropical forest in Africa, therefore, constitutes a much less substantial portion of the loss of this biome, at 5.4% of the worldwide loss within this biome between 2000 and 2005.

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