Occurrence, density, and distribution of longleaf pine regeneration in southeastern forests: An assessment by forest type, disturbance and site quality

Abstract

Regenerating longleaf pine is essential for the long-term sustainability of longleaf pine forest ecosystems and the important services those forests provide, particularly for endangered organisms. The objective of this study was to investigate the occurrence, density, and distribution of longleaf regeneration across a range of site quality, forest type, and disturbance regimes within the longleaf pine range from 1995 to 2019. We used 6,128 plots from multiple inventory cycles of the USDA Forest Service Forest Inventory and Analysis (FIA) dataset covering the entire longleaf pine range. The methods of analysis included logistic regression and the Inverse Distance Weighted (IDW) interpolation method. Two sets of measurements of 2,092 plots were used for change detection analysis. Longleaf regeneration was abundant in longleaf and loblolly pine-dominated stands. For a one-unit increase in the basal area ratio of longleaf pine trees in the plots, the probability of occurrence of longleaf pine seedlings and saplings increased up to 239% and 362%, respectively. The density and occurrence of longleaf regeneration were significantly greater on low-quality sites than on high-quality sites. Longleaf seedlings occurred with less frequency on disturbed sites, particularly by insects, diseases, and animals, than on undisturbed sites. Similarly, longleaf saplings were found with less frequency on sites disturbed by harvesting, weather, insects, diseases, and animals. We found a declining geographic range of longleaf pine trees, saplings, and seedlings during the 1995–2019 period. The density and ratio of longleaf seedlings decreased in about 25.2% and 14.0%, and increased in around 13.5% and 6.2% of the study area, respectively. Likewise, the density and ratio of longleaf saplings decreased in nearly 36.1% and 24.8% and increased in approximately 14.4% and 11.5% of the study area, respectively. Understanding the regeneration dynamics of longleaf pine is essential to restore and effectively regenerate longleaf pine forest ecosystems.