Just give your trees a billion health...
There will be noone that is going to sit there, waiting for 5 and a half YEAR to see that the tree goes down and to laugh at you.
it works in my map... the healing thing I mean.
My shredders do 3500 damage to trees, but when I use the heal effect they can't destroy trees. I think it's just because you can't see the effect of the tree being healed because it has no chest head and origin cause it's a tree.
I don't know how I can prove this really but... OH well