The environment of the United States comprises diverse biotas, climates, and geologies. Environmental regulations and the environmental movement have emerged to respond to the various threats to the environment.
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More than 400 mammal, 700 bird, 500 reptile and amphibian, and 90,000 insect species have been documented.[1] Wetlands such as the Florida Everglades are the base for much of this diversity.
Around 14,000 species of fungi were listed by Farr, Bills, Chamuris and Rossman in 1989.[2] Still, this list only included terrestrial species. It did not include lichen-forming fungi, fungi on dung, freshwater fungi, marine fungi or many other categories.
With habitats ranging from tropical to Arctic, U.S. plant life is very diverse. The country has more than 17,000 identified native species of flora, including 5,000 in California (home to the tallest, the most massive, and the oldest trees in the world).[3]
The country's ecosystems include thousands of nonnative exotic species that often harm indigenous communities of living things. Many indigenous species became extinct soon after first human settlement, including the North American megafauna; others have become nearly extinct since European settlement, among them the American Bison and California Condor.[4]
The U.S. climate is temperate in most areas, tropical in Hawaii and southern Florida, polar in Alaska, semiarid in the Great Plains west of the 100th meridian, Mediterranean in coastal California and arid in the Great Basin. Its comparatively generous climate contributed (in part) to the country's rise as a world power, with infrequent severe drought in the major agricultural regions, a general lack of widespread flooding, and a mainly temperate climate that receives adequate precipitation.
Following World War II, the West's cities experienced an economic and population boom. The population growth, mostly in the Southwest, has strained water and power resources, with water diverted from agricultural uses to major population centers, such as Las Vegas and Los Angeles. According to the California Department of Water Resources, if more supplies are not found by 2020, residents will face a water shortfall nearly as great as the amount consumed today.[5]
The lower 48 states can be divided into roughly five physiographic provinces: the American cordillera, the Canadian Shield, the stable platform, the coastal plain, and the Appalachian orogenic belt.
The Endangered Species Act of 1973 protects threatened and endangered species and their habitats, which are monitored by the U.S. Fish and Wildlife Service.
In 1872, the world's first national park was established at Yellowstone. Another fifty-seven national parks and hundreds of other federally managed parks and forests have since been formed.[6] Wilderness areas have been established around the country to ensure long-term protection of pristine habitats. Altogether, the U.S. government regulates 1,020,779 square miles (2,643,807 km²) , 28.8% of the country's total land area.[7] Protected parks and forestland constitute most of this. As of March 2004, approximately 16% of public land under Bureau of Land Management administration was being leased for commercial oil and natural gas drilling;[8] public land is also leased for mining and cattle ranching.
As with many other countries there are a number of environmental issues in the United States. Topical issues include the Arctic Refuge drilling controversy and the Bush Administration stance on climate change.
The protected areas of the United States are managed by an array of different federal, state, tribal and local level authorities and receive widely varying levels of protection. Some areas are managed as wilderness while others are operated with acceptable commercial exploitation. By international definitions, the United States has 7448 protected areas, not counting marine areas, as of 2002. These protected areas cover 578,000 square miles (1,500,000 km²), almost 16% of the land area of the United States.[1] This is also one-tenth of the protected land area of the world. U.S. marine protected areas cover an additional 347,000 square miles (900,000 km²) with varying levels of protection.
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