Spatial distribution of longleaf pine regeneration after natural disturbance: Implications for uneven-aged management

Many of the longleaf pine ecosystems in the Southeast are being converted to uneven-aged systems.  The rationale behind this management strategy is that an uneven-aged structure mimics conditions that result from natural disturbances including hurricanes and fire. Previous research has identified appropriate gap sizes to create with silvicultural treatments and the regeneration dynamics within those gaps.  Recommendations for converting to uneven-aged conditions include creating regeneration areas of at least 0.1 ha by cutting groups of mature trees.  A challenge with this strategy is designing the configuration of group openings across the landscape that approximate natural conditions and can also be sustained through multiple cutting cycles.  This research focuses on the distribution of age classes across space in areas affected by hurricane disturbance.  The study site is an 8 ha area in the northwest panhandle of Florida, that had been managed with a 3-4 yr prescribed fire regime.  Trees were stem-mapped, and classified by height class (only regeneration is reported here).  Spatial distribution was evaluated using the Ripley’s K statistic.  Not surprisingly, the results confirmed that regeneration was clustered in distinct patches of about 0.1 to 0.15 ha sizes. Each of these regeneration patches exhibited typical gap dynamics, with the tallest stems located in the center of the regeneration clusters.  Interestingly, the regeneration patches tended to be clustered themselves, sometimes with several distinct patches within a 0.5 ha area.  It is likely that these patches developed in the larger areas opened up by hurricane damage where randomly distributed residual overstory trees still survived.  The distinctness of regeneration patches may have developed in those large areas as a result of 'exclusionary' zones created by the few residual overstory trees. These results suggest that management strategies using uneven-aged reproduction methods should include a consideration of these spatial arrangements of group openings when attempting to mimic natural processes.