I think every true outdoorsman would agree that Humans (3 main causes) are the most destructive creature on the face of the earth. Add to that such critters as Beetles and the Gypsy Moth and that IMO would be the legitimate top 4.

Living in a rural area I have seen the destruction of hardwoods by Gypsy Moths. They can,will and do gobble up thousands of acres of hard wood forests in 1-2 years. IMO this far out ways any over browsing by deer in any part of the country. Over browsing does not destroy/kill a forest system. Humans and Bugs will.

If US Forest Service made it a top 5 list maybe the deer would have made a claim to fame.