Tree is now showing fresh foliage after repotting last month. Patch of moss is there no due aesthetical reasons but to cover cutting spot on one of the larger roots, to keep place permanently moist. It could help create new roots on the spot. Soon growth will be too strong, leaves will be too big as is with Ash trees. I still have to do some branch editing but is too soon to weaken the tree right now. Bunch of ants is already occupying moss patch, and they will bring some aphids as soon as they'll find some around. And then we will fight.
BTW, it is time to name the tree, I think it is good enough to have decent name, or "nickname". I thinking about it and I feel it is there in my mind, hidden somewhere. I just could not catch him yet. If you have any good idea which comes to your mind, leave me a comment. Thanks.