Do trees get completely removed from the map or do they 'die' (loose leaves)? I am making a mod that degrades tiles based on pollution and I want to remove trees that are over a certain pollution limit and 'dead' for some time. If your mod destroys trees in a similar way I will just put Recommended mod : link in the description.

There are multiple stages in my mod. It turns trees into a dead tree variant first before eventually completely removing the tree leaving only the stump (which will fade away as per vanilla). However if pollution levels get low enough for trees to start growing again a "dead" tree can revive into a normal tree (However this is fairly rare since pollution hardly ever goes down enough).

This is exactly what I wanted to do. I am currently working on regrowing grass if pollution is low enough and I will probably adjust the values at which tiles degrade to be similar to yours, so this could make a very good mod combination.