In reply to zimpara:
> you make a joke of some little roots destabilizing some rocks.
Not really, no - especially when it's quarried rock which could very likely have hidden flaws from the original blasting. If it was an old, disused quarry outside it would just be one of the normal risks that climbers deal with on a regular basis. But this is inside the climbing centre, and at the top of a rock face to which are bolted the steel supports for a very large climbing wall. If I were the owner of the climbing centre I'd be worried about potential liability if the trees were left to grow.