Actually old trees are pretty much done when it comes to soaking up carbon. New trees soak it up quite a bit as they grow. Clearing out old trees and planting new is good for the planet.
I don't know where you get your information from Elwar but it scares me you work anywhere near weaponry.
Old trees sequester far more carbon than young ones.
http://www.nature.com/nature/journal/v507/n7490/full/nature12914.html"large, old trees do not act simply as senescent carbon reservoirs but actively fix large amounts of carbon compared to smaller trees"
Also, geographic location plays a part - older trees in the tropical region sequester far more carbon than younger trees. And guess where we are cutting down trees at the most rapid rate. The tropics.