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Harvard Forest Symposium Abstract 2018

  • Title: Landscape variation in canopy nitrogen and carbon assimilation in a temperate mixed forest
  • Primary Author: Zaixing Zhou (University of New Hampshire - Main Campus)
  • Additional Authors: Scott Ollinger (University of New Hampshire - Main Campus)
  • Abstract:

    Canopy nitrogen (N) is a key factor regulating carbon cycling in forest ecosystems through linkages among foliar N and photosynthesis, decomposition, and N cycling. In this analysis, we studied landscape variation in canopy nitrogen and carbon assimilation in a temperate mixed forest surrounding Harvard Forest in central Massachusetts, USA by integration of canopy nitrogen mapping with ecosystem modeling, and spatial data from soils, stand characteristics and disturbance history. Canopy %N was mapped using high spectral resolution remote sensing from NASA’s AVIRIS (Airborne Visible/Infrared Imaging Spectrometer) instrument and linked to an ecosystem model, PnET-II, to estimate gross primary productivity (GPP). Predicted GPP was validated with estimates derived from eddy covariance towers. Estimated canopy %N ranged from 0.5% to 2.9% with a mean of 1.75% across the study region. Predicted GPP ranged from 797 to 1622 g C m-2 yr-1 with a mean of 1324 g C m-2 yr-1. Relationships between canopy %N and predicted GPP with forest types, soil drainage, and land use history were also examined. Estimated canopy %N was positively correlated with measured %N within deciduous and evergreen species and to their fractional abundance. The lowest estimated canopy %N values occurred in areas with historical land use classified as permanent woodlots and the highest values occurred in areas classified as having been old-unimproved pasture. Intermediate values occurred in stands that were historically cultivated and mowed for pasture. A strong, positive relationship was observed between canopy %N and field-measured aboveground net primary production, providing support for the prediction that spatial patterns in forest growth are associated with spatial patterns in canopy %N. At the landscape scale, PnET-II GPP was compared with predicted GPP from a previous project known as BigFoot and from NASA’s MODIS (Moderate Resolution Imaging Spectroradiometer) data products. Canopy %N explained much of the difference between MODIS GPP and PnET-II GPP, suggesting that global MODIS GPP estimates may be improved if broad-scale estimates of foliar N were available.

  • Research Category: Regional Studies; Forest-Atmosphere Exchange

  • Figures:
  • Zhou 2018 HFAbsFig1.JPG
    Zhou 2018 HFAbsFig2.JPG