Where did you find that 100 trees per acre figure? That sounded really low to me, so I did some googling and found numbers more along the lines of 300-400 per acre.

In fact, 100 trees per acre is the minimum to be classified as a forest in a particular program, and that's in Southern California, which is especially sparse land for trees. http://mountainsfoundation.org/uploads/media_items/landowner...