Land use conversion
"This is the biggest threat of all, and in this category the principal problem is the conversion
of tropical forests to agricultural uses and tree plantations. Thirty-six nations lost 10
percent or more of their forest cover in the 1990s. Moreover, short of out-and-out conversion, forest
richness is reduced by habitat fragmentation, fires, and other factors. The draining and filling of
wetlands of all types is also another type of land conversion that has greatly reduced natural
habitats. As noted, the best estimates we have are that at least a third of the earth's original
forest cover has been cleared and about half the wetlands have been destroyed.
"More than a third of the world's land surface has been converted to human use, and an additional third
could be converted to human use in this century. About 12 percent of the earth's land is classified
as "protected" in some variety of park or preserve, and much of this area remains threatened by logging
and development pressures.
Urbanization is also a major factor in land conversion. The conversion of agricultural lands, wetlands
and forests to urban and suburban uses is occurring rapidly in both industrial and developing countries.
Sprawl is not exclusively a problem of the wealthy nations. In 1900, there were sixteen cities with over one
million inhabitants. Today, there are around four hundred, nearly a hundred of them in China."