Panda

The loss of habitats—the places where organisms live and get the nutrients, water, and living space they need to survive—is the primary reason biodiversity is in decline.

When people cut down a forest, fill in a wetland, trawl a seabed, or plow a prairie, they change the natural habitat of the species that live there. Not only can such changes kill or force out many animals, microorganisms, and plants; they also can disrupt complex interactions among species.

In the long run, habitat destruction can disrupt human communities as well as those of plants and animals. Dams on rivers in the Pacific Northwest have produced inexpensive electricity and have redirected water for agriculture—but they’ve also interrupted salmon migrations, drastically lowering the number of salmon that reach their spawning grounds. As a result, wild salmon populations have dropped dramatically, causing economic hardship for those who depend on the salmon for their livelihood.

Here are some facts that help put habitat loss into focus:

• Less than one percent of North America’s original tallgrass prairie ecosystem remains.

• More than one-half of the original wetlands in the United States have been lost or severely degraded in the last 300 years as a result of draining and filling.

• More than 95 percent of the lower 48 states’ original primary forests are gone. The largest areas of primary forest are in the Pacific Northwest, where about 10 percent of the original forests remain.

• The Yellowstone River is the only large U.S. river (longer than 600 miles) that is not severely altered by dams.

• Between 90 and 98 percent of the nation’s rivers are degraded enough to be unworthy of federal designation as wild or scenic.

• In Arizona, about 90 percent of river and stream (riparian) habitat has been destroyed by dams, conversion to farmland, excessive pumping of groundwater, cattle grazing, and urban development.