Forest edges as a starting point for restoration of fire-dependent oak woodlands

Restoring oak woodlands in the interior South and Midwest of the United States remains a vexing challenge for restoration practitioners. Most restoration attempts involving frequent burning have not been successful at restoring open woodland vegetation or oak regeneration. This study reports preliminary results of a demonstration project initiated in 2004 in a 100-yr-old fire-suppressed upland hardwood forest in north Mississippi (historically an open oak woodland). The goals were 1) to reduce off-site tree densities using a combination of burning and chemical and mechanical methods, 2) to increase the abundance and diversity of plants indicative of open woodlands, and 3) to shift dominance of the sapling layer from off-site species (e.g., Liquidambar styraciflua) to upland oaks (e.g., Quercus stellata, Q. falcata, Q. velutina). A unique aspect of this project was to compare plots near a power-line clearing edge with those in the forest interior in both treated (thinned, burned) and untreated blocks. Fires were set in late September 2004 and early October 2006. Censuses in 2005 and 2007 indicated that thinning and burning appeared to be achieving all three restoration goals only in the forest edge plot. The relatively high light levels at the forest edge, which persisted for several years before this study, likely favored 1) the persistence of several open-woodland herb species at the edge (although at low densities), thereby providing a ready source of propagules to respond to thinning and burning, 2) successful recruitment of oaks into the sapling layer prior to the treatments, which enabled them to avoid topkill, and 3) vigorous regrowth of smaller topkilled oak stems. Together these results suggest that successful restoration will likely require thinning of off-site species, proximity to a source of propagules of open-habitat species, and sustained light levels combined with periodic protection from fire.