What's the meaning of "cumulative" in the context?

[Ilikepizza]

As shown below, what does it mean by "cumulative" here?

- 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.

cr: Reading section of TOEFL, an English proficiency test developed by ETS.

 

[Rover_KE]

Welcome to the forum.

Our rules state that you must provide the source and author of any quoted text.

 

[Ilikepizza]

Thanks for reminding me. I've given the source and author.

 

[teechar]

Reading section of TOEFL, an English proficiency test developed by ETS.

That's not enough! If you found it in printed form, tell us the author, publisher, and publication date. If you found it online, give us the link.