Silvicultural treatments for converting loblolly pine to longleaf pine dominance: effects on ground layer and midstorey vegetation

Abstract

AbstractQuestionsHow do management practices used to enhance longleaf pine (Pinus palustris) seedling survival and growth under a loblolly pine (Pinus taeda) canopy alter the structure of midstorey and ground layer vegetation? Do management treatments achieve general restoration targets for longleaf pine ecosystem structure?LocationMarine Corps Base Camp Lejeune, NC, USA within the Middle Atlantic Coastal Plain Ecoregion.MethodsFour levels of timber harvest were applied to loblolly pine stands: Control (uncut, basal area ~16.2 m2·ha−1), MedBA (residual basal area ~9.0 m2·ha−1), LowBA (residual basal area ~6.4 m2·ha−1) and Clearcut (residual basal area of 0 m2·ha−1). Within each canopy treatment, we applied three cultural treatments selected to facilitate longleaf pine seedling success: NT (untreated), H (chemical control of woody vegetation) and H + F (chemical control plus fertilization). Vegetation responses, including the abundance (cover) of ground layer vegetation and midstorey stem densities, were reported for three growing seasons (2008–2010) following canopy removal.ResultsThe ground layer was dominated by woody vegetation, and total vegetation cover generally increased with increasing canopy removal. Canopy treatment effects varied through time. Clearcut plots had higher total herbaceous and graminoid cover than MedBA and Control plots in 2008, while woody cover was significantly lower on Control plots than on LowBA and Clearcut plots in 2009. Clearcut plots had higher densities of loblolly pines than Control plots in 2009 and 2010. The herbicide treatment reduced hardwood densities, but increased loblolly pine densities, especially in 2010.ConclusionsSuccessful restoration prescriptions are often site‐specific because of different land‐use history, climate, site characteristics and starting conditions. To achieve the restoration objective of creating an open midstorey with an herbaceous‐dominated ground layer when converting loblolly pine stands to longleaf pine dominance on relatively productive sites with abundant hardwoods and aggressive loblolly pine natural regeneration, canopy retention can slow the rate of development of loblolly pine regeneration and herbicides reduce hardwood stem densities. Frequent, repeated burning would likely be required to further reduce woody vegetation and increase the relative abundance of herbaceous vegetation.