For everything there is a season, as the Bible says. All life forms live for so long, and then begin to decline in health and eventually die. Depending on the species, trees have a fairly long life span. White oak under good conditions can live 200-300 years. On average though, oak-hickory type forests like we have in east Tennessee reach maturity around 80-120 years of age and begin to decline in health.
Signs that trees are past their prime include large, open canopies with big limbs but short leaf supporting twigs. The very tops of the trees tend to be flat rather than rounded. Usually a tree begins to die back in the top, so there may be large dead limbs and branches high up in the tree. As it continues to decline, the main stem of the tree may develop decay and suffer insect and disease attacks. From an economic standpoint, the lower stem of the tree is where the money is, what’s called the butt log. So as the tree’s health declines, so does its dollar value. Nut production of old oak and hickory also declines, reducing the wildlife food value as well.
What to do with over mature trees depends on the landowner’s objectives. If left alone the old trees will gradually die, opening holes in the forest canopy that will let more sunlight penetrate to the forest floor. This will stimulate young trees growing beneath the main stand to begin growing faster. Eventually these will grow up into the openings and replace the dying old trees. This process favors shade tolerant trees such as maple, beech, sourwood and dogwood, and disfavors less shade tolerant species such as yellow poplar, oaks, and hickories.
If the landowner does not want to lose the economic value of the mature trees, then a harvest is needed. Harvesting needs to be carefully planned to minimize soil erosion and ensure that a desirable stand of trees can develop afterwards. There are several cutting methods to choose from, each one favoring certain species and disfavoring others.
If you suspect you have mature or over mature woodland and need some advice on them, contact your local state forester. He can inform you on the health of the trees and make recommendations on harvesting, timber contracts, marketing, etc.