Silviculture of Pine Stands

Historically, pine has been a larger component of the forest types on the Cumberland Plateau, but with southern pine beetle (Dendroctonus frontalis Zimmermann) outbreaks and recent lack of the kinds of forest disturbances needed to regenerate shade-intolerant pine, the acreage of pine has declined. Before 1950, natural pine and mixed pine-hardwood composed more than 2.5 million acres of forest land on the Plateau, primarily on the middle and southern Plateau in Tennessee and Alabama. Today, pine in natural stands, plantations, and mixed stands constitute less than one million acres or about 10 percent of the forest land on the Plateau (Clatterbuck and others 2006).

The reduction in the acreage of pine can be attributed to several factors (Clatterbuck and others 2006):

1. Shade intolerant pines cannot live in the understory and midstory beneath a dense pine overstory. Once pines die or are harvested, more shade tolerant hardwoods will dominate the regenerating stand unless silvicultural measures are taken to favor pines.

2. As pine was harvested, most landowners did not make necessary investments to regenerate their land back to pine.

3. Pines are fire tolerant and were able to regenerate and grow at the expense of fire intolerant species during the frequent fires prior to 1950. Pine seeds need bare mineral soil to regenerate. With the advent of statewide forest fire control in the early 1950s, conditions necessary to regenerate pine diminished.

4. Outbreaks of southern pine beetle have reduced pine acreage. Usually hardwoods or mixed stands replace pine types if provisions are not made to regenerate pine.

5. Mixed pine-hardwoods stands are difficult to maintain because the shorter-lived pine is slowly replaced by hardwoods, resulting in a shift to more hardwood-dominated stands.

The amount of natural pine on the Plateau is decreasing because pines are pioneer species on disturbed sites and are gradually replaced by hardwoods in the absence of disturbances, particularly fire. Natural pine can be easily regenerated through clearcutting, seed tree, and shelterwood regeneration methods, but site preparation (chemical, mechanical, or fire) provisions must be made to create environmental conditions for controlling competing vegetation that otherwise would prevent pine seed from germinating and prospering. In the absence of beneficial site preparation, usually hardwoods will displace pine.