Last few years I have lost or losing several mature trees on my property....
Last few years I have lost or losing several mature trees on my property. Bakeri Blue Spruce, Ornamental Cherry and a Purple Plum. Seems that a few branches a year die, eventually the tree dies. The common denominator, looks to be a "fungus" that grows on the major branches (see photos)
Montgomery County Maryland
What you have photographed is a lichen, which is a symbiosis between an alga and a fungus which does not hurt your tree. Lichens grow on trees in areas where air is clean enough for their growth. http://extension.umd.edu/learn/i%E2%80%99m-lichen-it-peak-season-lichen-peeping
It is not uncommon for lichens to grow more luxuriantly on trees that are rotting, but lichens do not cause damage to trees. If your trees are already dead, we probably cannot say what killed them. If you have a tree that is currently sick and would like for us to try to diagnose it, please send photos and specific information about each individual tree. Different trees have different problems. vw