Damaging a tree with impact or physical damage generates some leaves. 0.13.0: Added fire. Fire will spread between trees and cause forest fires, causing a large amount of pollution to be released. 0.12.0: Trees degenerate slowly when there are high pollution levels. Trees regenerate health...
Regardless of whether the tree loses leaves or gets grayer, 10 pollution are absorbed by the tree. A tree stops losing leaves/becoming more gray once the sum of its gray percentage and its leaves lost percentage is above 120%. 50% of trees stop their leaf progression one stage earlier...