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Harvard Forest Symposium Abstract 2018

  • Title: Carbon fluxes exchange in a typical deciduous needle-leaf boreal forest
  • Primary Author: Jialin Liu (Harvard University)
  • Additional Authors: Roisin Commane (Harvard); J. William Munger (Harvard University)
  • Abstract:

    Boreal forests cover 33% of global forest area. Larch is the only deciduous conifer species in the global boreal forests which has unique ecological and environmental features when comparing with evergreen conifers. However, few studies have characterized the carbon exchange of larch species in boreal forests. Therefore, the net carbon exchange was measured in a Eurasian Dahurian larch (Larix gmelinii) forest in 2015 and 2016 by eddy covariance techniques. We simulated the carbon fluxes using an empirical tuned to the eddy covariance fluxes and explored mechanisms that regulate the larch productivity.
    Results showed satellite solar-induced fluorescence responded better to forest's photosynthesis than MODIS enhanced vegetation index did in the larch. Analysis on responding of net ecosystem exchange to environmental factors indicated temperature and precipitation were directly regulations for net ecosystem exchange, while the radiation tended to constrain gross primary production preferentially so that its restrictions were offset by the temperature dependency of the total ecosystem respiration. In the modeling section, net ecosystem exchange and gross primary production predicted by the empirical model were pretty consistent with referenced approaches (referred to FLUXNET general method), indicating reasonable model performance for the larch. However, discrepancies of total ecosystem respiration revealed the cross-validation was necessary for the separation of flux-tower observations. Unbalanced water conditions across years reduced the model accuracy, particularly during the spring onset. By scaling up our results using the empirical model, we found boreal larch forest in Eurasia (approximately 1.5 million km2) is still a significant carbon sink with the averaged magnitude of 646.4 TgCO2/yr. Yet flux observations in several northern spruce and pine forests from the FLUXNET dataset showed signs of carbon neutral or slightly carbon sources.
    Beyond better understanding ecosystem's environmental responses and carbon fluxes patterns in the rarely studied larch boreal forest, this study was designed to complement magnitudes of boreal larch's carbon exchange to the global scenarios, and to improve the precision and accuracy of global scale carbon assessment in the future.

  • Research Category: Forest-Atmosphere Exchange

  • Figures:
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