Relationships between forest structure and soil CO2 efflux in 50-year-old longleaf pine

Abstract

Global climate change and the accumulation of the greenhouse gas, carbon dioxide (CO2), in the atmosphere, may be mitigated by the proper management of soils and forests through carbon (C) sequestration. Longleaf pine (Pinus palustris Mill.) forests, which historically dominated the upper and lower Coastal Plain in the southeastern United States, have the potential to sequester large quantities of C through long rotations and temperate climatic conditions. Soils compose the largest C sinks on earth and thus have potential to be the largest contributors of CO2 to total ecosystem respiration. More knowledge on the effects of stand and community structure on soil CO2 efflux is needed to understand how forest management influences C cycling. The objective of this study was to examine how forest structure and forest characteristics influence the rate of soil CO2 efflux to better understand forest management effects on C pools. Soil CO2 efflux was examined over a 10 month period on the Escambia Experimental Forest near Brewton, AL in response to basal area, root biomass, woody debris in the soil, soil charcoal mass, soil C, litter depth, litter mass, downed woody debris, aboveground and belowground biomass, ground cover, and environmental conditions. Basal areas ranged from 7 to 36 m2∙ha-1 and ground cover, litter mass, litter depth, soil woody debris, and downed woody debris varied with basal area but soil temperature did not. Mean monthly soil CO2 efflux ranged from 1.6 µmol m-2∙s-1 in January to 6.5 µmol m-2∙s-1 in August 2008. Soil CO2 efflux increased exponentially with soil temperature and temperature explained 96% of the variation in soil CO2 efflux. Only 1-11% of the variation in soil CO2 efflux was explained by soil moisture, litter mass or depth, ground cover, natural log-transformed live coarse roots, downed woody debris C, or natural log-transformed soil charcoal. These results indicate that soil CO2 efflux can be modeled using soil temperature and that forest management practices that influence soil temperature rather than forest structure or forest characteristics per se will influence soil CO2 efflux.