@Mandragola: The trees do look good with that mud on them, gives them a nicely non-uniform and natural look. The grey sludge of WW I is, oddly enough, an eerily beautiful sight on these models. If you wanted to push the shelled out look a bit further, maybe consider clipping some branches off and lay them in the mud? With full, rounded branching still on the trunks, they look more singed than shelled, unlike the very hard hit ground around them.
Even when there's some branches left, it'll be like this:
I've thought about this sort of thing. Looks very difficult to achieve, but potentially very effective if done right.
I've currently got two methods of doing trees: these brass ones and the broken paintbrushes for stumps. But in either case there should really be branches everywhere.