Green trunks clean the air!
Why do some trees in a forest have greenish bark?
If you see something green growing on a tree trunk, it’s most probably lichens or mosses.
Mosses are non-vascular plants. Lichens, on the other hand, are composite organisms consisting of a symbiotic relationship between an alga and a fungus. Lichens are epiphytic, which means that they merely use trees as a place to grow. Their colors vary form gray to green, orange or even black.
Lichens offer a clue to air quality. Because they are intolerant of pollution, lichens do not often grow on city trees.
Lichens or mosses growing on a tree trunk do not mean that the tree is diseased and do not damage it in any way.