or is it dying because of this? =====>>>> the second pic ... shows fungus which indicates that the interior has been dead long enough.. in tree time.. for the interior to rot .. imo ... i should be removed ... and then you will find out if the rot goes into the trunk ... not seeing the whole thing .. when you say there is overall decline ...i would speculate that if there is not much left of the tree .. its probably a goner.. in tree time ... in the mean time.. you can learn a lot about pruning and tree health.. by pruning it over the next few years.. and just observe what happens ... when removing a large branch ... start out at the perimeter.. and work your way to the trunk ... removing hanging weight so that by the time you get to the trunk .. you can make a clean proper cut ... the best thing for that project is a good tree saw ... ken ps: if you like the tree .. perhaps for spring flower ... now would be the time to perfect the ID and plant a new one.. so as this one declines ... the new one will get settled in and growing ... in spring.. get pix of flowers and leaves for the ID ...

Evidently, it is foliose lichen type https://www.bing.com/images/search?q=foliose+lichen&FORM=HDRSC2 , but it is all I can help you with, sorry.

The differing opinions above prompted me to conduct my own research. A fungus, an alga, and sometimes cyanobacteria living symbiotically are referred to as lichen. Whether their symbiosis is mutualism or parasitism in its nature is a matter of debate, since the relationship is fairly complex and not yet fully known. As I understand, the relationship is the following (in a very simplified way): the fungus, through its thallus structure and through release of certain beneficial fungi chemicals, provides its photobionts (alga and cyanobacteria) with optimal living conditions. Additionally, fungus absorbs minerals (mainly carbon and nitrogen) from the air and water, and makes them available to its photobionts. In exchange, alga converts carbon to simple sugars which the fungus feeds on, while cyanobacteria provides the fungus with nitrogen, converted to a form the fungus can actually use. Many view the above relationship as mutualism; others argue it’s parasitism, because the fungus consumes more than half the sugars produced by the alga, sugars which the alga also needs for itself. Whatever the case may be regarding the nature of the symbiotic relationship between the lichen-forming organisms, I think it’s generally agreed upon the fact that the lichen does not parasitize the substrate it lives on; so it won’t harm a tree or other thing it attaches itself to, because it doesn’t feed on that substrate. My question was whether or not anyone could tell me if it’s a moss or a lichen, and perhaps even identify it by its name. However, I’m glad the discussion took this turn, because I’ve now gained a great deal of appreciation for lichens. Still, if anyone happens to know the name of this particular lichen, please let me know. Thanks everyone.

it actually doing its job.. using and breaking down the mulch .. its natures way ... basically its composting your mulch ... nothing to fix here ... but its pretty cool .. except for the name.. lol ... ken