The effects of fire on soil-surface carbon dioxide (CO2) efflux, FS, and microbial biomass carbon, Cmic, were studied in a wildland setting by examining 13-year-old postfire stands of lodgepole pine differing in tree density (< 500 to > 500 000 trees ha−1) in Yellowstone National Park (YNP). In addition, young stands were compared to mature lodgepole pine stands (∼110-year-old) in order to estimate ecosystem recovery 13 years after a stand replacing fire. Growing season FS increased with tree density in young stands (1.0 µmol CO2 m−2 s−1 in low-density stands, 1.8 µmol CO2 m−2 s−1 in moderate-density stands and 2.1 µmol CO2 m−2 s−1 in high-density stands) and with stand age (2.7 µmol CO2 m−2 s−1 in mature stands). Microbial biomass carbon in young stands did not differ with tree density and ranged from 0.2 to 0.5 mg C g−1 dry soil over the growing season; Cmic was significantly greater in mature stands (0.5–0.8 mg C g−1 dry soil). Soil-surface CO2 efflux in young stands was correlated with biotic variables (above-ground, below-ground and microbial biomass), but not with abiotic variables (litter and mineral soil C and N content, bulk density and soil texture). Microbial biomass carbon was correlated with below-ground plant biomass and not with soil carbon and nitrogen, indicating that plant activity controls not only root respiration, but Cmic pools and overall FS rates as well. These findings support recent studies that have demonstrated the prevailing importance of plants in controlling rates of FS and suggest that decomposition of older, recalcitrant soil C pools in this ecosystem is relatively unimportant 13 years after a stand replacing fire. Our results also indicate that realistic predictions and modeling of terrestrial C cycling must account for the variability in tree density and stand age that exists across the landscape as a result of natural disturbances.
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