Hardwood-pine mixedwoods stand dynamics following thinning and prescribed burning
Restoration of hardwood-pine (Pinus L.) mixedwoods is an important man-agement goal in many pine plantations in the southern Cumberland Plateau in north-central Alabama, USA. Pine plantations have been relatively un-managed since initiation, and thus include a diversity of hardwoods developing in the understory. These unmanaged pine plantations have become increasingly vulnerable to insects, and management activities were initiated to facilitate transition towards hardwood-pine mixedwoods. We evaluated a combination of thinning and prescribed fire prescriptions in a randomized complete block design with a 3 × 3 factorial treatment arrangement and four replications of each treatment. Treatments were combinations of thinning to three residual basal areas (no thin, light thin to 17.2 m2 ha-1, heavy thin to 11.5 m2 ha-1) and three prescribed burn applications (no burn, one burn to be repeated every 9 years, three burns repeated every 3 years). Burning without thinning altered stand structure by reducing overstory stem density by 15 %, whereas thinning without burning reduced density by 70 % and burning coupled with thinning resulted in reduced overstory trees by 72 %. Frequent fire had the greatest impact on midstory structure and regeneration. Midstory stem density was reduced by 90 % following thinning and burning. Oaks (Quercus L.) and red maple (Acer rubrum L.) were the most com-mon understory species after thinning only, burning only, and thinning com-bined with burning. There were more oak and red maple seedling sprouts following frequent burning. Currently, >75 % of red maple sprouts dominate the regeneration, compared to only 40 % of the oaks. Although the treat-ments have accelerated the transition toward hardwood-pine mixedwoods, the fate of oak and which hardwood species will be dominant in the future remains uncertain.