Annual growth in longleaf (Pinus palustris) and pond pine (P. serotina) in the Sandhills of North Carolina is driven by interactions between fire and climate

Abstract

Understory fires are important for the maintenance of pine savanna ecosystems of the southeastern U.S., which contain high biodiversity and numerous federally endangered species. Prescribed burns are administered to maintain the open structure of pine savannas, conserve biodiversity, and to reduce wildfire hazard. However, relatively little research has examined which factors control the effects of prescribed burns on mature trees, and how responses might be altered by changing climate. The impact of prescribed burning on growth responses is likely to vary by tree species and by environmental conditions. To test the importance of these factors, tree cores were taken from mature Pinus palustris and Pinus serotina individuals at multiple locations across Fort Bragg, NC, a military preserve with detailed records on prescribed burn history dating back to 1991. Individual trees were sampled along the hydrologic gradient from xeric uplands to streamside wetlands. Annual growth was modeled as a function of species identity, hydrologic position, fire history, and climate conditions. We determined that prescribed burning produced a moderate decline in annual growth indicating that stress from prescribed burns outweighs benefits from increased water and nutrient availability. We found that the negative effects from prescribed burning were diminished or reversed during warmer years, and that the model predicts potential increases in growth during burn years under anticipated climate change scenarios. Surprisingly, there were no significant differences in growth rate by species or hydrologic position. Together these findings suggest that while prescribed burns may have minor, short-term impacts on tree growth under most current conditions, these effects are small enough that they are unlikely to outweigh the many benefits of this management technique for other aspects of ecosystem structure.