Something growing on my trees
You have lichens growing on the trunk and also some algae and moss at the base of the trunk. The green lichen growing on the dead branch is different than the white lichen growing on the base of the tree. The dark green looks like moss. Here is a link to more information about lichens.
They are not harming the tree just growing on the outside of it. While the lichens are not harming the tree and are common on the trunks of older trees, I seldom see them on younger trees that are growing well. There might be something wrong with the tree so it is in poor vigor but the lichens are just taking advantage of a place to grow. It is normal for branches in the interior of older trees to die and fro the tree to shed the dead branches.