Effects of snow cover variations on spatial patterns of carbon emissions in northern forests

Background/Question/Methods

Winter snow regulates terrestrial carbon (C) cycling by modifying micro-climate, but a comprehensive assessment and understanding at the process level is missing in ecosystem models. Here, we investigate the effect of winter snow variation, i.e., the timing and duration, on C fluxes from northern forests at two different spatial scales using eddy covariance measurements and ecosystem model simulations.

Results/Conclusions

We found that flux site observational ecosystem respiration (R_eco) and net ecosystem C exchange (NEE) were correlated with fluctuations of soil temperature controlled by variation in snow depth, but not correlated with the variation of air temperature. Winter R_eco and NEE ranged from 0.03-1.9 gC·m^-2·day^-1 according to site observations, and the Biome-BGC modeled winter NEE for northern forest ecosystems was approximately 0.96 Petagram (1 Pg = 10¹⁵ gram) of C per year during the period between 1982 and 2009. A statistically significant change in model simulated winter R_eco was noticed in Eurasia, with a decreasing rate at 0.61-1.21 gC·m^-2·yr^-1 in Siberia. Both increasing and decreasing trends of winter NEE were observed in North America, which resulted in an altered C emission pattern with a relatively stable total winter R_eco. Across the entire study area, the winter R_eco decreased 0.21 gC·m^-2·yr^-1, which accounts for approximately 20% of the enhanced annual C sink in the northern forest area. In total, reduced snow cover increased soil freezing potential, and temporarily suppressed the winter C efflux by 0.83 Pg of C during entire the 27-year study period.