A fun way to eliminate hollow trees is to knock a small hole in the base, and build a fire in the bottom. Stand back and in a few hours if there is an escape hole at the top, it will burn off. As kids, a friend and I loved findin hollow trees like that. We were little pyros, but besides the trees, never did any serious damage.

The first one was in his parent's back yard during a dry summer. He tossed a match down a knot hole and forgot about it. An hour or so later he gave me a call, so I came over to see a tree spewing flame throwers out of knot holes up high, and the tree roaring like an angry animal. It was fascinating and scary at the same time. Running a hose into it has no effect other than some steam. Eventually the tree collapsed and we got it out, but he sure got in trouble when his parents got home! Kind of hard to hide a missing tree in the back.