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Grad student talk - Colder snowmelt in a warmer world reduces forest carbon uptake

Thursday, November 12, 2015, 4:30PM - 5:30PM


Taylor Winchell


RL-1 room 269

Seasonally snow-covered environments represent a large portion of global terrestrial carbon sequestration. During the snow ablation period, water availability associated with snowmelt promotes photosynthetic carbon uptake, while snow cover diminishes carbon losses from soil respiration. Although the ablation period can be as short as two weeks, as much as 30% of the total seasonal carbon uptake can occur during this period in high elevation, subalpine forests. Varying ablation period dynamics, however, can result in varying rates of carbon uptake during this integral uptake period. We use 15 years of observational climate flux and snow water equivalent (SWE) data for a subalpine forest in the Colorado Rocky Mountains to analyze carbon uptake trends during the annual ablation period. Specifically, we focus on how the timing and magnitude of peak SWE affect carbon uptake during the ablation period. We find that when the snowmelt period occurs one month earlier than average, the forest experiences an ablation period mean air temperature of 2.7° C, approximately 5° C colder than an ablation period that occurs one month later than average. This early, colder atmospheric condition leads to daytime carbon uptake rates that are 2.5 gC/m2/day less than the later, warmer period, which results in 47 gC/m2 less ablation period carbon uptake. As most climate models project peak SWE to occur earlier under various warming scenarios, we can expect to see a trend of less carbon uptake during future ablation periods. We expect to see a decrease in total growing season carbon uptake if the post-snowmelt period is unable to compensate for the decrease in ablation period carbon uptake.