Characteristics of gaps and natural regeneration in mature longleaf pine flatwoods ecosystems

Developing uneven-aged structure in mature stands of longleaf pine requires scientifically based silvicultural systems that are reliable, productive and sustainable. Understanding seedling responses to varying levels of site resource availability within forest gaps is essential for effectively converting even-aged stands to uneven-aged stands. A project was initiated on the Apalachicola National Forest in Northwestern Florida to examine these relationships, particularly as they would apply to the group selection forest reproduction method. This study used a line transect technique to examine gaps formed in mature stands of longleaf pine by either natural disturbances or prior intermediate silvicultural operations (i.e., thinnings). The expanded gap sizes ranged from 32 to 1161 m^2; however, 86% of all gaps sampled in this study were less than 600 m2 in size. Mean and median expanded gap sizes were 402 and 334 m^2, respectively. Gap shapes were irregular and significantly different from a circle. Seedling stocking ranged from 0 to 43% and density ranged from 0 to 9800 seedlings ha^-1. Neither gap size nor shape significantly affected seedling numbers or root collar diameters (RCDs). In contrast, proximity to mature longleaf pine affected both seedling numbers and RCD. Seedling numbers increased considerably >=5 m from mature trees. Significant decreases in seedling RCD, resulting from interspecific competition with mature longleaf pine, were detected and most strongly expressed outside the gaps (average RCD=21 and 16 mm inside and outside gaps, respectively). In general, seedling stocking within the gaps was low (average 16%).