Many North American animals depend on dead trees and tree cavities. A lack of suitable cavities often limits how many of these animals can use your woods. This slideshow gives examples of North American creatures that depend on cavities for homes and nests.
Wildlife biologists advise that you have at least six cavity trees per acre. If you don’t have that many, you can create tree cavities using a cordless drill and this advice from the Cornell Lab of Ornithology.
Perhaps the best known visual signs of old-growth forests are their truly enormous trees. You can accelerate large tree growth in your woods by finding your healthiest “legacy trees” and removing competing trees around them so the big trees can grow faster.
If your woods are short on snags (standing dead trees), you can create some of this valuable wildlife habitat by girdling trees. Girdling kills a tree while leaving it standing so it can become a snag.
True old-growth forests have greenery at every level from the forest floor to the top of the canopy. You can start some new growth on the ground using small patch cuts, which remove every tree from an area less than an acre.