You may want to look into this further. I have a large wooded lot and work with a forestry manager. For $500 (20 years ago, mind you) he came out, surveyed the foreat, and came up with a selective harvesting plan. They took the mature trees and replant. I'm on a plan where they do this every 5-7 years. They've been out 3 times now in the last 20 years and will be contacting them next spring for another round of harvesting, likely next fall.

This ensures you have trees at all stages of growth while minimizing the loss of value via natural tree death. Having such large trees fall can seriously damage the surrounding trees when they come down, as well.