Climate

Due to the United States' large size and wide range of geographic features, nearly every type of climate is represented. The climate is temperate in most areas, tropical in Hawaii and southern Florida, arctic in Alaska, semiarid in the Great Plains west of the Mississippi River, desert in the Southwest, mediterranean in coastal California, and arid in the Great Basin. Extreme weather is not uncommon—the states bordering the Gulf of Mexico are prone to hurricanes and most of the world's tornadoes occur within the continental United States. However, the predominantly temperate climate, infrequent severe drought in the major arable regions, and infrequent severe flooding have helped make the nation a world leader in agriculture.

America's weath­er is affected markedly by the con­frontation between polar continen­tal air masses (usually cold, dry, and stable) and tropical maritime air masses (warm, moist, and unstable). Most parts оf America are subject to a generally westerly wind flow that tends to move weather systems eastward.

The interaction of climatic controls creates a pattern of climatic regionalization. In the East, the principal element in climatic varia­tion is temperature; in the West, it is precipitation. In the East, the divi­sions between the climate regions are based largely on the length of the growing season—the period from the average date of the last frost in spring to the first frost in fall—and on the average summer maximum temperature or winter minimum temperature. In the West, average annual precipitation is the key, although moderated tem­peratures are an important aspect of the marine West Coast climate. In the East, the more northerly areas are generally drier; in the West, they are colder. In the East, the major influence on climatic varia­tion is latitude; in the West, it is topography.

Vocabulary notes

Cropland- зерновые поля

Pastureland- пастбища

Urban- городской

Coastline-побережье

Vast- широкий, обширный

Valley-долина

Copper - медь

Lead - свинец

potash – углекислый калий

tungsten - вольфрам

timber - древесина

hazard- опасность

permafrost – вечная мерзлота

impediment - преграда

commonwealth - содружество

Deciduous - лиственный

Prevail - превалировать

boreal - арктический

altitude – высота над уровнем моря

flat - плоский

fertile - плодородный

distinct - индивидуальный

mediterranean - средиземноморский

arid – сухой, засушливый

drought - засуха

arable - пахотный

precipitation - осадки

annual - ежегодный

latitude - широта

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.