Howie said the dead fall timber has combined with the introduced wolves to begin to bring back the aspen groves which the overpopulated elk had browsed down to clumps of shrubs. 

The dead fall around the aspen  protects them from elk browsing;  the dead fall cuts off escape routes and makes the elk too nervous to stand and browse, as they prefer more open areas with clear escape routes should a wolf or other predator approach.  Thus protected, the shrub aspen are forming groves again.