Group selection silviculture for converting pine plantations to uneven-aged stands

Abstract Recent years have witnessed an increased 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 approach to induce natural regeneration and convert pine plantations to uneven-aged stands. In a wet flatwoods site in north-west Florida, we characterized natural regeneration (density, size, spatial distribution, hot spots) of slash pine (Pinus elliottii Englm.) eight years following group selection harvests and one year following prescribed fire in mature slash pine plantations. Our study utilized a long-term, operational scale experiment consisting of circular harvest group openings of four different sizes (0.1, 0.2, 0.4, 0.8 ha), each replicated three times. In all group openings, we stem mapped all regeneration > 1.37 m in height and measured their diameter at breast height (dbh) and total height. We also estimated understory shrub cover in the group openings. Overall, slash pine regeneration response was highly variable across group opening sizes and ranged between 150 (in 0.1 ha group openings) to 670 stems ha−1 (in 0.8 ha group openings). On average, 468 ± 105 (mean ± standard error) stems ha−1 were found in the group openings. Group opening size had no significant effect on regeneration density or size (ɑ =0.05). Position within group opening, however, had a significant effect on regeneration density and height, with higher density occurring in group opening centers and taller stems in northern positions. Shrub cover decreased with increasing group opening size and was lowest in northern positions. Dense shrub cover (60–100%) was associated with greater regeneration density. The areas with dense shrub cover appeared to have escaped prescribed fire and experienced lower seedling mortality. Spatial point pattern analysis showed aggregation of regeneration for all group sizes across all distances. Regeneration hotspots were mostly central and southern positions in group openings. Earlier observations of our study suggest that the group selection harvesting may be a suitable approach to regenerate slash pine and add an age-class (regeneration cohort) to even-aged stands in wet flatwoods sites.