Anthropogenic climate change is expected to cause a decrease in peak annual snow water equivalent (SWE) and lead to a shift in the timing and rate of snowmelt to earlier and slower regimes in the mountains of the Western United States. High-elevation forests in these mountain ranges represent a critical and vulnerable sink in the global carbon cycle. Understanding the snow hydrology of subalpine forests is crucial for assessing the health of these sinks. The Niwot Ridge Long Term Ecological Research station (NWT), located in the southern Rocky Mountain, maintains co-located sensors in a subalpine forest that provide over 20 years of continuous SWE and eddy covariance data. Previous studies show that longer growing season length and reduced net CO2 assimilation at NWT are correlated with shallower snowpack and earlier spring onset. Results of previous studies of carbon uptake rely on methodology. These methods were reevaluated and linear regression analysis was performed on snowmelt, meteorological, phenological, and ecosystem productivity variables over the entire 20-year record of data from NWT. Peak carbon uptake is correlated with magnitude peak SWE (R2=0.54) and the timing of both snow disappearance (R2=0.38) and spring onset (R2=0.30). Further, both the timing of peak carbon sequestration and spring onset are correlated with snowmelt and meteorological variables. Differences in methods yield stark differences in regression significance for phenologically-derived variables. These results reinforce the evidence for water limitation of the subalpine ecosystem at Niwot Ridge and highlight the need to monitor the effects of snowmelt on carbon exchange of high-elevation forests in the Western United States.
Geography Graduate Student, CU Boulder