Effects of prescribed fire and thinning on tree recruitment patterns in central hardwood forests

Second-growth oak forests in the central hardwoods region are considered compositionally unstable in the absence of large-scale disturbances. While prescribed burning and mechanical thinning treatments are potential options for managing succession in mixed-oak forests, few studies have adequately studied tree successional patterns in mature (> 100-year old) stands following application of these anthropogenic disturbances. In a randomized block factorial design, we studied tree recruitment patterns (stems < 10 cm dbh) in three mature southern Ohio forests that contained stands divided into four treatment units (each approximately 30 ha): control, prescribed fire, mechanical thinning, and mechanical thinning followed by prescribed fire. Treatments were applied in the dormant season of 2001. A single prescribed fire reduced seedling and sapling densities of Acer rubrum, the understory dominant in these forests. A. rubrum rapidly recovered to pre-treatment levels in all treatment units four growing seasons following the disturbances, largely by colonizing from seed and resprouting from top-killed sapling regeneration. Mechanical thinning treatments accelerated understory recruitment of early-successional, shade-intolerant tree species that regenerated from seed (e.g., Liriodendron tulipifera) and resprouted from a seedling bank (e.g., Sassafrass albidum). Oak (Quercus spp.) seedlings < 140 cm tall densities were unresponsive to all treatments over the 4-year study period, although densities were dynamic through time. Seedling densities of Q. alba and Q. prinus declined in all treatments over the 4-year study period, while seedling densities of Q. velutina increased in all treatments. Oak seedling sprouts were not released from growth suppression in silviculturally thinned or burned forests. Four growing seasons following treatment application, oak regeneration remained at a competitive disadvantage with high densities of early-successional species present in xeric and intermediately moist portions of thinned stands. To maintain adequate oak recruitment in these forests, our data suggest that prescribed fire may need to be applied several years following a mechanical thinning treatment. Periodic fires are predicted to control the strong resprouting response of A. rubrum and fast-growing opportunistic tree species. (c) 2006 Elsevier B.V. All rights reserved.