Gap-Scale Disturbance Processes in Longleaf Pine (Pinus Palustris Mill.) Woodland

Abstract

Forest disturbances influence stand succession and developmental patterns. The most localized and frequent disturbances, gap-scale events, remove large branches, individual trees, or small groups of overstory trees. The formation of canopy gaps can lead to an increase in resources including light and growing space for the residual stems in proximity to the gap.Longleaf pine (Pinus palustris) has experienced a 95% range decline since European settlement. Longleaf pine establishment and recruitment has been found to be enhanced by canopy gaps.Gap-scale disturbance processes have been studied in Coastal Plain longleaf pine ecosystems, but not in montane longleaf pine woodlands. To better understand gap-scale processes in montane longleaf pine woodlands, I sampled 50 canopy gaps and 20 non-gap (i.e. reference) plots at Reed Brake Research Natural Area in the Oakmulgee Ranger District of the Talladega National Forest, Alabama, USA. I collected data on canopy gap characteristics including canopy gap formation mechanisms, closure mechanisms, and canopy gap and non-gap species composition. Increased understanding of gap-scale processes in longleaf pine woodlands will allow for better management of these endangered ecosystems. The most common canopy gap formation mechanism among sampled gaps was snags (38%) followed by snaps (32%), and the majority of canopy gaps were formed by the death of a single tree (64%). The most common closure mechanism was lateral crown expansion (74%), and longleaf pine was the most common species predicted to capture canopy gaps. I used LiDAR data to examine canopy gap size and gap fraction across the study area. The average area of observed canopy gaps sampled, and the average observed area of LiDAR detected gaps were similar (75 m2, and 76 m2 respectively). For canopy gap, and non-gap plots, the most important tree species was longleaf pine, the most important sapling species was Vaccinium arboretum, and the most important seedling species was also Vaccinium arboretum. Based on these results, I predict that under the current disturbance regime longleaf pine will remain the dominant species in this stand. This study increased our knowledge of longleaf pine woodland gap fraction, as well as the composition of canopy gaps and non-gap areas.