Example of fir waves on one of the hills around Katahdin as seen from the Knife Edge. These form when one tree falls and the resulting gap exposes trees on the leeward edge to higher winds. They are more likely to die and expand the gap downwind. Then young trees start to grow in the wind shadow and are protected from the winds. The combination of dying trees and growing trees make up the fir wave in the direction of the prevailing wind. OK, enough of a lesson for you, see Wikipedia for more info and links to articles on this if you are really interested.