Recent years have witnessed increasing interest in managing and restoring southern pine stands using uneven-aged silvicultural strategies, that rely on natural regeneration. Group selection harvests are regarded as an effective reproduction cutting approach to induce natural regeneration and convert shade-intolerant pine plantations to uneven-aged stands. In a mesic-wet flatwoods site in north-west Florida, we comprehensively characterized natural regeneration (density, size, spatial distribution, hot spots) of slash pine, Pinus elliottii, eight years following group selection harvests of mature slash pine plantations. Specific questions included: 1. Is regeneration density sensitive to gap size, position in the gap or plant competition? 2. Is regeneration growth related to gap size, position in gap or plant competition? 3. Does the spatial pattern of regeneration depend on gap size, position in the gap or density of competing vegetation? Our study utilized a long-term, operational scale experimental set up consisting of harvest-created circular gaps of four different sizes (0.1, 0.2, 0.4, 0.8 ha), each replicated three times. In all gaps, we stem mapped all regeneration >1.37 m in height, measured their diameter at breast height (dbh) and total height. We also estimated understory shrub cover in the gaps. We created tree regeneration kernel density maps and interpolated shrub cover maps for all the gaps to examine regeneration density responses spatially.
Results/Conclusions
Regeneration response was highly variable across the gaps and varied between 0.0 to 960 stems ha-1. On average, 468 stems ± 105 SE ha-1 were found in the gaps. Gap size had no significant effect on regeneration density or size, although both tended to increase with increasing in gap size. Position within gap, however, had significant effect on regeneration density, with higher density observed in the southern positions of the gaps and gap centers. Shrub cover decreased with increasing gap size and was lowest in northern sections of gaps. Dense shrub cover, in parts of the gaps, appeared to have disrupted the effect of prescribed burns leading to greater surviving regeneration and density. Spatial point pattern analysis using Ripley’s K function showed aggregation of regeneration for all gap sizes. Overall, slash pine regeneration distribution in gaps was highly clustered and appeared to have been greatly influenced by microsite conditions and impact of prescribed fire. The occurrence of 468 stems of >1.37 m height per hectare in gaps following 8 years of harvest suggest group selection provides adequate regeneration for uneven-aged stand conversion in slash pine flatwoods ecosystems.