Here in the PNW, moss and lichen grows on trees like my paperbark maple (Acer griseum), especially during a wet spring like the one we're having, just as abundantly as it does on soil. It doesn't need to be removed and it doesn't imply that the tree is unhealthy. It won't hurt the tree.
In fact, it's quite beautiful, don't you think?
Moss and lichen on paperbark maple
Anna at Flutter & Hum hosts Wednesday Vignette. Check out her post here.