新托福TPO19阅读原文及译文(二).docx

新托福TPO19阅读原文(二):ession, Climax, and Ecosystems
TPO19-2:ession, Climax, and Ecosystems
In the late eenth century, ecology began to grow into an independent science from its roots in natural history and plant geography. The emphasis of this new "community ecology" was on position and structure munities consisting of different species. In the early twentieth century, the American ecologist Frederic Clements pointed out that a ession of munities would develop after a disturbance such as a volcanic eruption, heavy flood, or forest fire. An abandoned field, for instance, will be invaded essively by herbaceous plants (plants with little or no woody tissue), shrubs, and trees, eventually ing a forest. Light-loving species are always among the first invaders, while shade-tolerant species appear later in the ession.
Clements and other early ecologists saw almost lawlike regularity in the order of ession, but that has not been substantiated. A general trend can be recognized, but the details are usually unpredictable. ession is influenced by many factors: the nature of the soil, exposure to sun and wind, regularity of precipitation, chance colonizations, and many other random processes.
The final stage of a ession, called the climax by Clements and early ecologists, is likewise not predictable or of position. There is usually a good deal of turnover in position, even in a munity. T