Earlier snowmelt reduces atmospheric carbon uptake in midlatitude subalpine forests

Authors

  • Taylor S. Winchell,

    Corresponding author
    1. Institute of Alpine and Arctic Research, University of Colorado Boulder, Boulder, Colorado, USA
    2. Department of Civil, Environmental, and Architectural Engineering, University of Colorado, Boulder, Colorado, USA
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  • David M. Barnard,

    1. Institute of Alpine and Arctic Research, University of Colorado Boulder, Boulder, Colorado, USA
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  • Russell K. Monson,

    1. Department of Ecology and Evolutionary Biology and Laboratory for Tree Ring Research, University of Arizona, Tucson, Arizona, USA
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  • Sean P. Burns,

    1. Department of Geography, University of Colorado Boulder, Boulder, Colorado, USA
    2. National Center for Atmospheric Research, Boulder, Colorado, USA
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  • Noah P. Molotch

    1. Institute of Alpine and Arctic Research, University of Colorado Boulder, Boulder, Colorado, USA
    2. Department of Geography, University of Colorado Boulder, Boulder, Colorado, USA
    3. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California, USA
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Abstract

Previous work demonstrates conflicting evidence regarding the influence of snowmelt timing on forest net ecosystem exchange (NEE). Based on 15 years of eddy covariance measurements in Colorado, years with earlier snowmelt exhibited less net carbon uptake during the snow ablation period, which is a period of high potential for productivity. Earlier snowmelt aligned with colder periods of the seasonal air temperature cycle relative to later snowmelt. We found that the colder ablation-period air temperatures during these early snowmelt years lead to reduced rates of daily NEE. Hence, earlier snowmelt associated with climate warming, counterintuitively, leads to colder atmospheric temperatures during the snow ablation period and concomitantly reduced rates of net carbon uptake. Using a multilinear-regression (R2 = 0.79, P < 0.001) relating snow ablation period mean air temperature and peak snow water equivalent (SWE) to ablation-period NEE, we predict that earlier snowmelt and decreased SWE may cause a 45% reduction in midcentury ablation-period net carbon uptake.

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