I have heard an old tale and have seen it true. When I was a kid my Dad said there was a day in May that you could cut a ring around a tree and by the end of the day the leaves would wilt. The tree would die and fall down within a year. We did this and it worked but we can't remember the day. Can anyone letmeno???
Any time a tree is "girdled" that way, the sap is cut off ... death follows. A non-energetic way to clear land at any rate.
It's why young trees often have wire mesh around the base so animals can't nibble off the sweet tasty new bark.