Relationships between Soil CO2 Efflux and Forest Structure in 50-Year-Old Longleaf Pine

Interest in restoration of longleaf pine (Pinus palustris Mill.) in the southern United States offers opportunities for carbon (C) sequestration. To better understand C fluxes in longleaf pine, soil CO2 efflux (SR) and forest C pools were measured in 50-year-old stands varying in basal area from 7 to 36 m(2) ha(-1). Soil CO2 efflux measured monthly ranged from 1.6 to 6.4 mu mol CO2 m(-2) s(-1) and was strongly related to soil temperature and only weakly related to basal area and forest characteristics associated with varying basal area. The annual sum of SR ranged from 11.0 to 17.9 Mg C ha(-1) year(-1). Litter mass explained the majority (38%) of the variation in annual SR among plots varying in basal area. Standing C stocks, which included longleaf pine aboveground and below-stump biomass, litter, soil C, live and dead fine and coarse roots (all species), down deadwood and buried coarse woody debris, ranged from 63.8 to 176.8 Mg C ha(-1). Similar SR but low longleaf pine net primary productivity in low basal area stands suggests that those stands were carbon sources; however, more information on the contribution of the herbaceous layer to ecosystem net primary productivity and SR is needed. FOR. SCI. 58(5):472-484.