Threats to Biodiversity and Ecosystems

Threat #1

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."
 
Threat #2

Land Deregulation
"The productivity of crop and grazing land is threatened by water and wind erosion, by salinization and water-logging of irrigated lands, and by over grazing and devegitation. Most severe in arid and semiarid regions, these processes often occur in combination, and their effects referred to as desertification. About three-fourths of the world's drylands are degraded, and about a fourth of all land is degraded to a degree sufficient to reduce its productivity. Replacing depleted agricultural land is one of the drivers behind deforestation"
 
Threat #3

Freshwater Shortages
"As freshwater is diverted from watercourses for agricultural, urban, and industrial uses, national in-stream habitat is lost or diminished, and water supplies that feed forests and other systems decline. An estimated 20 percent of normal river flow globally is now extracted for human use. Water withdrawals climbed sixfold in the twentieth century, twice the rate of population growth, and the trend continues. Freshwater withdrawals for irrigation and other purposes are estimated to grow by 40 percent by 20202. With 40 percent of the world's people already living in countries that suffer from serious water shortages, the prognosis for freshwater habitat is not good. The following rivers no longer reach the sea in the dry season: the Colorado, Yellow, Ganges, Nile, Syr Darya and Amu Darya. Is California an indication of things to come? Ninety percent of the state's wetlands have disappeared, and 60 percent of the native fish species are extinct or at risk of extinction."
 
Threat #4

Watercourse modifications
"Natural waterways are often dammed, channelized, or diverted and the swamps and other wetlands associated with them drained or filled, with serious consequences for the biota associated with streams, rivers, and estuaries. Sixty percent of the world's major river basins have been severely or moderately fragmented by dams and other construction."
 
Threat #5

Invasive species
"Non-native, invasive species have emerged as the second most serious threat to biodiversity, after habitat destruction. For example, about 40 percent of all species listed in the United States today as endangered or threatened are so listed primarily because of the threat posed by invasives. Invasives now cover one hundred million acres across the United States and cost the country an estimated $137 billion annually. Thousands of marine species move around the planet every day in the ballast water of cargo ships."
 
Threat #6

Overharvesting
"This the most serious threat to marine fisheries, including cod, bluefin tuna, Atlantic halibut, and salmon. Current logging rates threaten mahogany. The global market in birds and other wildlife is about ten billion dollars a year, and many species are taken at unsustainable rates. A fourth of the trade in wildlife relies on illegal poaching."

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Quoted from:
Red Sky at Morning - America and the Crisis of the Global Environment
by James Gustave Speth
Yale University Press - 2004