Vegetation

In most of the inhabited portions of America today the "natural" vegetation, if it ever existed, has been so substantially removed, rearranged, and replaced that it seldom is found now. In the Southeast, for example, the original mixed broadleaf and needle leaf forests were cut and replaced by the economically more important needle leaf forests. The grasses of the plains and prairies are mostly European imports. Their native American predecessors are gone either because they offered an inferior browse for farm animals or because they could not withstand the onslaught of modern humanity and its imported weeds. Most of what climax vegetation remains is in the West and North.

The tundra of the far North is the result of a climate that is too cold and too dry for the growth of vegetation other than grasses, lichens, and mosses. Tundra exists in small areas far southward into the United States, where climatic conditions at high elevations are inhospitable to tree growth. Northward, the altitu-dinal tree line is found at lower elevations until, eventually, the latitudinal tree line is reached.

With habitats ranging from tropical to Arctic, U.S. plant life is very diverse. The country has more than 17,000 identified species of native flora, including 5,000 just in California (which is home to the tallest, the most massive, and the oldest trees in the world). More than 400 species of mammal, 700 species of bird, 500 species of reptile and amphibian, and 90,000 species of insect have been documented. Wetlands such as the Florida Everglades are the base for much of this diversity. The country's many ecosystems include thousands of non-native exotic species that often adversely affect indigenous plant and animal communities.

Vocabulary notes

Inhabited - населенный

Vegetation - растительность

Broadleaf - широколиственный

Needle leaf - хвойные

Predecessor - предшественник

Browse - бродить

Withstand – устоять, выдержать

Onslaught - нападение

weeds - сорняк

lichens - лишайник

mosses - мох