Nearly half -- 46 percent -- of the world's forest has been converted to farms, pastures, and other uses over the past 80 centuries. While just over half remains, most of it has been heavily altered by people and bears little resemblance to pristine forest. According to this assessment just 22 percent of Earth's original forest remains in large, relatively natural ecosystems. (See "Figure 2. What Happened to the Forests that Once Covered the Earth?".)

Of the remaining frontier forest that is left, nearly half is boreal forest. (See "Percent of the World's Frontier Forest"). A broad belt of primarily coniferous trees, boreal forests lie between arctic tundra to the north and warmer, temperate forests to the south. They blanket much of Alaska, Canada, Russia, and Scandinavia.

For two reasons, boreal forests have been less disturbed than have other forest types. First, long winters, poor soils, and other factors make farming difficult, so little forest has been converted to agriculture. Second, boreal trees, particularly in northern areas, tend to be slow-growing, scrawny, and widely dispersed. So until modern technology, increasing wood demand and other factors changed the picture, commercial loggers traditionally had little incentive to exploit boreal forests.

Temperate forests, on the other hand, are the most heavily fragmented and disturbed of all forest types. This study concludes that just 3 percent of today's frontier forests are temperate stands (another 5 percent contains both temperate and either boreal or tropical frontier forest). Thriving in a moderate climate, pristine temperate forests once extended throughout most of Europe, much of China and the continental United States, as well as parts of Canada, Australia, New Zealand, Chile, and Argentina.

Thanks to their favorable climate and fertile soils, temperate forests were the first to be cleared wholesale by humans. By 1000 B.C., most of eastern China's forests had been converted to farmland.[21] More than 2,000 years ago, the Greeks and Romans destroyed much of the forest that rimmed the Mediterranean.[22][23] Today, the frontier forests of the Middle East and Mediterranean Basin are completely gone. Western Europe's frontier forests were leveled during the Middle Ages as new cities and towns spread throughout the region.[24]

Temperate forests of the Americas, Australia, and New Zealand were opened relatively recently -- over the past few centuries -- by European explorers and settlers. Although indigenous peoples had long lived in and shaped these forests, newcomers wrought far more dramatic changes. (See "Frontier Forest Myths".) Even so, almost all of the world's remaining temperate frontier forests are in these three regions.

Until this century, tropical forests -- located in warm regions within 30 degrees of the equator -- remained largely intact. In the past few decades, however, they have fallen with alarming speed. Between 1960 and 1990, some 450 million hectares were cleared -- a fifth of the world's entire tropical forest cover. (See "Percentage of the World's Tropical Forest Cleared Between 1960 and 1990")

Millions more hectares have been degraded by logging, agricultural clearing, and the removal of vegetation for fuelwood, building materials, and livestock feed. In Asia and Africa, for example, this study found that though roughly a third of the original forest cover remains, less than 10 percent of this original cover still qualifies as frontier forest. (See Total Area in Original, Current and Frontier Forest)

Worldwide, most frontier forests are now restricted to scattered, widely dispersed pockets, many located in inaccessible mountains or swamps. Europe -- which has already lost two thirds of its historical forest cover -- maintains only a few small patches of frontier forest totalling less than 1 percent of the original, all in Sweden and Finland.

The lion's share of today's frontier forest -- more than 75 percent -- is located in just three large tracts covering parts of seven countries: two blocks of boreal forest -- one stretching across much of Canada and Alaska and the other in Russia -- and one large relatively undisturbed chunk of tropical forest spanning the Northwestern Amazon Basin and Guyana Shield.

References and notes

20. Geographic Information Systems are used to store, analyze and display spatially-referenced (map) data.

21. United Nations Environment Programme (UNEP), Global Biodiversity Assessment, (Cambridge, Cambridge University Press, 1995), p. 345.

22. Alexander Mather, Global Forest Resources, (Portland: Timber Press, 1990), p. 32.

23. Jack Westoby, Introduction to World Forestry, (Oxford: Basil Blackwell Ltd., 1989), p. 50.

24. Jack Westoby, Introduction to World Forestry, (Oxford: Basil Blackwell Ltd., 1989), pp. 54-5.