Understory dynamics in North Carolina longleaf pine savannas: Biodiversity, dominance, and biomass

Abstract

AbstractQuestionsRestoration of ecosystems is complex, with multiple targets that can work in concert or conflict with each other, such as biodiversity, species dominance and biomass. When properly managed, longleaf pine (LLP) savannas are among the most biologically diverse habitats in the world. However, anthropogenic influences, such as fire suppression, have decimated this ecosystem and its biodiversity, making restoration a priority. Here, we describe the biodiversity and community dynamics seen in the understory layer across xeric LLP savannas in North Carolina and then answer the following questions: What are the predictors of (1) biodiversity, (2) dominance and (3) biomass at multiple spatial scales?LocationFifteen observational study sites in North Carolina spanning from the Sandhills to the Coastal Plain.MethodsAt each of the 15 sites, 25 sampling plots were established where above‐ground herbaceous biomass, species presence and abundance, soil characteristics and light availability were measured along with numerous other environmental variables.ResultsConsiderable variation exists across study plots within and across sites, with plant species richness ranging from 1 to 17 per m2. The relative cover of the dominant grass species,Aristida stricta(wiregrass), also varied greatly within and across sites, with a median of ca. 30% relative cover per plot. Wiregrass was a significant predictor of biomass and biodiversity at small scales. With increasing wiregrass abundance, richness decreases, with 25% relative wiregrass cover leading to the highest levels of biodiversity. Likewise, because wiregrass abundance is one of the stronger predictors of above‐ground biomass, we also found a unimodal richness–biomass relationship.ConclusionsOur results indicate that at lower ends of the productivity and richness gradients, land managers can increase all three restoration targets in the understory at the same time; however, at more diverse and productive sites, restoration practitioners may need to prioritize one target or find a balance between all three.