Is there a way to enable trees spreading to landfill terrain? When I use the mod they don't grow on landfills and those created by "TREEEES" or saplings mods are actively killed off by this mod. It doesn't seem to be counting landfills as tiles and just deleting the trees like if they grew on stone in the middle of my base: they are instead turned into dead trees and left there.

Landfill has no fertility rating by design making trees not grow there. You can either change my code and add a fertility rating to landfill here: https://github.com/NoxyNixie/Noxys_Trees/blob/master/control.lua#L228 or you can use a mod like landfill painting and paint a more fertile tile.

I made a pull request that adds an option for trees growing on landfill, prod the mod owner to merge it in :)
https://github.com/NoxyNixie/Noxys_Trees/pull/12