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Harvard Forest Symposium Abstract 2006

  • Title: Clouds, a controlling factor in terrestrial carbon uptake
  • Primary Author: Qilong Min (SUNY at Albany)
  • Additional Authors: David Fitzjarrald (SUNY at Albany); Shuyu Wang (SUNY at Albany)
  • Abstract:

    The interaction of climate with regional characteristics of ecosystems imposes complex and varying limitations on carbon uptake in different vegetation and climate regimes in the world. Recent studies suggest that climate change, along with alteration of co2 fertilization, N deposition and land-use characteristics, alters the global terrestrial ecosystem through several controlling factors in terrestrial carbon uptake (e.g. temperature, precipitation, and radiation). However, the presence of clouds can both cause and be the consequence of changes in these controls, and subsequent impacts on stomatal dynamics through changes in leaf temperature and leaf-to-air vapor pressure deficit (VPD). Clouds also modulate solar radiation and photosynthetically active radiation (PAR) in favor of photosynthesis through changes of its spectral distribution (or light spectral quality) and diffuse component.





    Although clouds are intrinsically linked to key factors of climate variability, its role in the interannual variation of terrestrial exchange on ecosystem or larger scales has received relatively little attention. We examined interannual variabilities of temperature, precipitation, and cloud as well as their effects on carbon uptake by analyzing 13-year turbulent exchange and radiation measurements in a northern hardwood forest. We found that both cyclic and secular variabilities of clouds, as modulated by the large scale atmospheric circulation, strongly mediate the interannual variability of carbon uptake, shown in Figure 1. Other factors, however, show statistically weak relationships with carbon uptake. This demonstrates that clouds, their mean value and distribution during the growing season, are the controlling factor in driven the interannual variability of the terrestrial carbon uptake.





    The Figure caption:


    Scatterplots of NEE, GEE, and RESP as functions of transmittance index, precipitation, and temperature for the growing summer from 1992-2004.


  • Research Category: Forest-Atmosphere Exchange