Patterns of vegetation composition and diversity in pine-dominated ecosystems of the Outer Coastal Plain of North Carolina: Implications for ecosystem restoration

Abstract

Terrestrial ecosystems of the Atlantic coastal plain have experienced considerable change over the past two centuries, largely due to agricultural activities and fire suppression and exclusion. Many areas that were once dominated by open longleaf pine (Pinus palustris) woodlands now support closed canopy stands of loblolly pine (Pinus taeda) with a dense midstory of broadleaved shrubs and trees. In recent years, efforts to restore the herbaceous plant communities typically found in fire-maintained longleaf pine woodlands have focused on the use of midstory thinning to produce savanna-like conditions and to facilitate the restoration of historical fire regimes through prescribed burning. Previous efforts to restore longleaf pine stands have focused on the potential of fire-suppressed longleaf pine woodlands, which have been met with some success. However, it is unclear what the potential is for loblolly pine stands to act as a ’surrogate’ environment for the restoration of the often species-rich herbaceous layer of longleaf pine woodlands. To assess the effectiveness of longleaf pine restoration treatments in existing loblolly pine stands, we analyzed the drivers of plant community composition in loblolly pine stands with mechanical midstory removal treatments, untreated loblolly pine stands, longleaf pine stands, and pond pine dominated high-pocosin systems. We sampled 75 plots, from which more than 200 individual plant taxa were identified, with species richness (number of species per 0.1ha) ranging from 9 in pond pine pocosins to 118 in longleaf pine woodlands. Plant species richness and composition varied in response to soil properties, with the first NMS ordination axis correlated with soil properties related to soil moisture and organic matter content (SOM), and the second NMS ordination axis correlated to the concentration of certain soil nutrients (P, Ca), the variability of which may be due, in part, to historic fertilizer applications. While stand types were largely distinct from each other in their vegetation composition, there was nevertheless some compositional overlap among some longleaf and loblolly pine stands. Areas of compositional overlap appear to have somewhat similar soil properties, whereby the soils found in overlapping loblolly pine stands were closer to those found in longleaf pine stands (i.e. low SOM content). Thus, an assessment of the soil properties of loblolly pine stands may allow for an identification of candidate sites for which longleaf pine restoration treatments may be most effective.