Here in our area the main forest type is called oak-hickory, meaning oak and hickory species take up the majority of the forest canopy (the tops of trees where the sunlight is). There are millions of acres of oak-hickory forests across the eastern US, and they provide very valuable timber and wildlife benefits. Unfortunately statistics from almost every state indicate that oak-hickory forests are slowly converting to other tree types, especially beech, birch, maple, and yellow poplar.
On dry sites oaks seems to be able to regenerate themselves because competition from other species is not as severe. These places include south and west facing slopes, and the upper slopes of ridges. On moist sites like hollows, lower slopes, north and east facing slopes, young oak seedlings are not able to compete with other trees, especially maple and yellow poplar. Foresters have tried to favor oak regeneration through the type of harvesting method that is used to cut timber. And while some work okay, there is still room for improvement.
Some folks want to protect oak-hickory forests by never cutting them, using hands off forest management. Doing this leaves the forest floor continuously shaded. Oak is not as tolerant to shade as species like maple and beech, and these species will dominate the layer of young trees beneath the larger ones. As the old oaks and hickories die out, shade tolerant trees replace them.
A selection cut, where only trees here and there are harvested, still leaves most of the forest too shady for oaks to grow properly, thus favoring maple and beech growth.
Foresters recognize the shade problem, and have often recommended clear cuts to open up the forest floor to full sunlight and thereby help the baby oaks to develop. This unfortunately favors fast growing yellow poplar, which takes advantage of full sun to grow really fast and out pacing the oak.
None of the traditional harvest treatments get back the oak we would like. So how do we do it? Research is looking at the possibility of using prescribed fire to help even the playing field. Oak seedling develop a sizable root system before they put on much height growth, which is the reason they are poor competitors… they are slow out of the gate. Competing species like maple and yellow poplar tend to favor height growth over root growth to be able to get out in front of the race for sunlight. So theoretically if you burn an area and top kill the seedlings, the oaks have good reserves in their roots and will sprout back a strong stem. The poplar and maple on the other hand don’t have good root reserves and don’t bounce back so well, thus favoring oak. This would be a tricky management method requiring careful and expert use of prescribed fire, so we will see how the research plays out.
Steve Roark is the Area Forester in Tazewell, Tenn. for the Tennessee Department of Agriculture, Forestry Division.