Sentence:  [C]ommunity types may represent either climax plant associations or successional communities within a <WSD>sere</WSD>. 
Meaning of the word marked with <WSD> tags:  A natural succession of animal or plant communities in an ecosystem, especially a series of communities succeeding one another from the time a habitat is unoccupied to the point when a climax community is achieved. (from early 20th c.)