That would be me. Yes there is lots of thick moss on the maple and cottonwood trees. In fact, I cut what looked like an 8 inch diameter limb off and it turned out to be about an inch thick. The rest was moss.
Yes. There is volcanic ash and dirt in or under the moss. Yes it dulls chains. So, that's why I file by hand, and have skip chain. If I scraped the moss off each time, it would take me longer to cut the &#@ blowdowns out of the road and I'm already slow enough. It takes me about the same time to change to a different chain. So I just file.
The real genuine timber fallers don't have to worry much about moss. It likes hardwoods. They cut conifers, and have nicer, cleaner wood to cut. There might be just a little bit of moss on the hemlocks, but not much.
For a while, after the volcano blew, they chopped off the bark where they would cut to fall the tree. They don't do that anymore.