That sounds pretty grim WILF, hitting trees worries the hell out of me, but cant be avoided sometimes. One time many years a go, I had dog chasing a roe through a thin windbreak of trees the dog struck at speed which caused the roe to slam side on into a tree, The Roe was near enough dead from the impact when I got there and the dog looking confussed, he was lucky that day! just goes to show how it can all go wrong so quickly. Are dogs need pleanty of luck in their lives.
Would be nice to see a pic of your hound.
Regards Sirius