Distribution, composition, and productivity of longleaf pine ecosystems in the southeastern US have changed considerably in the last decades. The lack of disturbance and fire has been a major factor limiting the natural regeneration of longleaf pine in mixed forests. Conservation of longleaf pine is a high-priority of forest management on both private and public land. Poor natural regeneration of longleaf pine in the mixed oak-pine forests of the southeast has received considerable attention from landowners and conservation professionals, but has not been studied as extensively as regeneration in pure longleaf-pine stands. We investigated the vegetation structure and occurrence of longleaf pine seedlings in oak-pine forest types of four southeastern states. We used data from 1503 plots of the US Department of Agriculture Forest Inventory and Analysis (FIA) Program collected during recent inventory cycles between 2005 and 2013. Our analysis included logistic regression with penalized maximum likelihood estimation, canonical correlation, analysis of variance, and community structure analysis. Using a logistic regression model, we predicted the probability of longleaf seedling occurrence in response to different environmental, stand, site and disturbance factors.
Results/Conclusions
There were a total of 119, 111, and 121 tree species in the seedling, sapling, and overstory layers across the plots, respectively. Longleaf pine seedlings, saplings, and trees were present on only 32, 37, and 121 plots, respectively, out of a total of 1503 plots. The dominance ranking of longleaf pine across the plots for seedlings, saplings, and trees was 50th, 27th, and 23rd, respectively. The most frequent longleaf pine associates in the overstory were loblolly pine, turkey oak, sweetgum, slash pine, mockernut hickory, and southern red oak. The data indicated that the occurrence of the longleaf pine seedlings is an infrequent event in southeastern oak-pine forest types. Seedling, sapling, and tree density of longleaf pine increased with the decrease in site productivity. Mean annual temperature, Shannon’s diversity index, stand density, longleaf pine overstory density, and overstory longleaf pine purity ratio had a significantly positive relationship with the occurrence of longleaf pine seedlings. Disturbance, however, showed no significant relation with longleaf regeneration on the sample plots. These findings can help forest managers in designing and implementing silvicultural treatments to promote the natural regeneration of longleaf pine in oak-pine forests.