托福阅读应试技巧
Plant communities assemble themselves flexibly， and their structure depends on the particular history of the area. Ecologists use the term “succession” to refer to the changes that happen in plant communities and ecosystems over time. The first community in a succession is called a pioneer community， while the long-lived community at the end of succession is called a climax community. Pioneer and successional plant communities are said to change over periods from 1 to 500 years. These changes―in plant numbers and the mix of species―are cumulative. Climax communities themselves change but over periods of time greater than about 500 years.
Plant communities assemble themselves flexibly， and their structure depends on the particular history of the area. Ecologists use the term “succession” to refer to the changes that happen in plant communities and ecosystems over time. The first community in a succession is called a pioneer community， while the long-lived community at the end of succession is called a climax community. Pioneer and successional plant communities are said to change over periods from 1 to 500 years. These changes―in plant numbers and the mix of species―are cumulative. Climax communities themselves change but over periods of time greater than about 500 years.
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