Biophysical controls of CO2 flux through snow in lodgepole pine and clearcut ecosystems

Soil CO₂ efflux is the dominant component of carbon loss in most terrestrial ecosystems. Wintertime respiration, both heterotrophic and autotrophic may account for significant contributions to annual carbon losses from the terrestrial belowground carbon pool to the atmosphere in temperate, boreal and arctic ecosystems, but the magnitude of this flux and physical transport mechanisms through snow are unclear. In addition, the role of forest disturbance, succession and management on snow distribution and accumulation as it relates to biogeochemical fluxes remains uncertain. We hypothesize that a lack of aboveground vegetative structure in a lodgepole pine clearcut will result in greater exposure to wind events and advective transport of CO₂ through snow. We quantified wintertime CO₂ flux, snow depth, density, and temperature, wind speed, soil moisture and temperature, and air temperature at forested and clearcut sites in the Tenderfoot Creek Experimental Forest (TCEF) in west-central Montana, USA. The clearcut site experienced a deeper snowpack in comparison to the forest site in early winter. Snowpack depth was similar between sites in midwinter, but the forest snowpack was deeper in spring, with corresponding changes to soil temperature as it was insulated by snow. Snow density, and thereby resistance to trace gas flux, tended to be higher in the clearcut site. Soil and subniveal CO₂ concentrations were higher in clearcut during early winter but higher in the forest during spring. CO₂ flux thus followed different cold-season patterns between the two sites. Quantifying flux processes and their correlation to snow physical properties may lead to a better understanding of how anthropogenic and climatic change influence the carbon cycle in temperate, boreal and arctic ecosystems.