Soil trace gas fluxes in response to wildfire and forest management in Colorado ponderosa pine ecosystems

Background/Question/Methods

Since the Industrial Revolution, atmospheric concentrations of the greenhouse gases carbon dioxide (CO₂), methane (CH_4­), and nitrous oxide (N₂O) have increased by 35, 150, and 45%, respectively. These changes are the result of fossil fuel combustion, agriculture, and land use change. In this study, we focused on understanding how wildfire and forest management practices affect the exchange of these trace gases between the soil and the atmosphere either by directly altering biotic activity or indirectly through environmental changes.

Results/Conclusions

Our findings suggest that CO₂ fluxes increase in the years after a wildfire, and that local scale variables such as soil moisture, temperature, and fire severity are important controlling factors for these trace gas fluxes. We found that CO₂ and N_2­O fluxes were significantly affected by interactions among forest management practices that include thinning, chipping, and fertilization, and that these impacts varied throughout the growing season, likely as a result of seasonal changes in soil moisture. Finally, we used the ecosystem simulation model Daycent to extend our field studies over broader spatial and temporal scales in examining the effects of fire and fire suppression. Simulated methane uptake showed minimal changes in response to fire, but Daycent estimated a 13 – 37 % decrease in N₂O and NO fluxes, and gross nitrification rates during the fire suppression era relative to before the suppression era. Ninety-eight percent of the global warming potential of the soil CO₂, CH₄, and N₂O fluxes was contributed by CO₂. Our studies suggest that over the long-term, soil CO₂ fluxes, and thereby carbon cycling, are the most sensitive to changes in the biota and physical environment that fire and forest management generate.