There are six aspens in my yard. In early summer brown spots started appearing on the leaves fo two trees and the leaves began falling and are halfway bare now. Now a third tree in a different location is doing the same thing. My parents have a couple trees doing the same thing and I've noticed similar problems with at least two neighbors. Anyone else seeing this? One local nursery said it happens from time to time with Aspens and is caused by stress in the environment/weather. Others have said it might be bores, but I don't see any signs. Any experts out there?