And people have spent millennia over-extracting plants, leading to erosion and desertification and subsequent changes of local weather patterns (precipitation, humidity, etc).

If they'd known to replenish and make broader use of their defecations and organic waste, they might well have kept their 'jungle'.

Certainly, it appears to have worked for ancient Amazonian tribes who are thought to be responsible for much of the quality land in the Amazon basin, much of which would otherwise be quite shallow and sandy with low nutrients.