They didn't need trees to survive, as proven by their survival. The claim is that their population hit a plateau due to the space available for farming, instead

They didn't need trees to survive, as proven by their survival. The claim is that their population hit a plateau due to the space available for farming, instead of dramatically collapsing as previously claimed. If survival is the metric for success, then they didn't permanently damage their environment. As much as we love trees that's hard to imagine, but that's my interpretation of the study.