Features advanced tree recognition features! A tree is only counted as a tree if it stands on one of the blocks defined in the config at "tree-ground-blocks" (by default grass, mycelium, dirt and coarse dirt) and contains no more than "max-air-in-trunk" blocks of air (by default 1).
This update renames your config.yml to config.old.yml and creates a new one, so you have to transfer your config changes if you don't want to use the new default settings.