托福阅读真题+题目+答案：Succession in Plant Communities

托福阅读真题+题目+答案：Succession in Plant Communities

In the nineteenth century, plant biologists began placing greater emphasis on how plants fit into communities. ▋This growing focus on the history of plant communities led to a critical concept in ecology: the theory of succession, which hypothesizes an orderly sequence of changes in plant communities leading to a stable climax community. ▋According to succession theory, changes in plant communities should follow orderly laws, and competition for space, light, and water would determine the patterns of those changes. ▋After a disturbance such as fire destroys a forest, succession theory predicts that grasses would first invade the site, followed by shrubs that would crowd out the grasses.▋ Soon certain tree species would displace the shrubs, and under the shade of the first trees, other tree species more tolerant of shade would come in and eventually eliminate the original species. Competition-for light, for water, for space-would determine the patterns of forest changes.
1.The word “displace” in the passage is closest in meaning to

A.add to

B.grow taller than

C.force out

D.put at risk

2.According to paragraph 1, which of the following statements is NOT in accordance with succession theory?

A.Plant communities change in an orderly and predictable manner.

B.Grasses tend to crowd out shrubs and follow them as the main species at a site.

C.Eventually the composition of a plant community stops changing and stabilizes.

D.The main cause of changes to plant communities is competition for light, space, and water.

In the late nineteenth century, Henry Cowles, working on the sand dunes of Lake Michigan, formalized the idea of dynamic vegetational succession. After a major disturbance, such as a fire that burns down all the trees on a site, the first species to colonize are those that best exploit the conditions of the disturbed site-lots of sun but little water or nutrients. Soon, however, these pioneer species change the environment in ways that make their own continued survival difficult-they create so much shade that their seedings (young plants) cannot survive. They moreover cool the soil surface, contribute organic matter to the soil, and increase soil moisture, all of which favor the invasion of the community by more shade-tolerant species.
3.According to paragraph 2, what are the characteristics of the pioneer species that occur after an area has been cleared by a fire?

A.Their seedlings are most resistant to fire.

B.They make the environment difficult for other species to survive in.

C.They are able to change the environment to suit their needs.

D.They need lots of light, little water, and few nutrients.

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