How does an old mature undisturbed hardwood forest change over a 25 year time span?

Old growth forests tend to have large trees and standings dead trees multi layered canopies with gaps that result from death of individual trees and coarse woody debris on the forest floor depending on the trees it can last anywhere from century to several millennia. Hardwood forests of the eastern united states can develope old growth chacteristics in one or two generation of trees or 150-500 years.