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Harvard Forest Symposium Abstract 2012

  • Title: Inferring long-term carbon sequestration from tree rings at Harvard Forest: A calibration approach using tree ring widths and geochemistry / flux tower data
  • Primary Author: Soumaya Belmecheri (University of Arizona)
  • Additional Authors: Kenneth Davis (The Pennsylvania State University); Stockton Maxwell (The Pennsylvania State University); Alan Taylor (Pennsylvania State University (all campuses))
  • Abstract:

    Improving the prediction skills of terrestrial carbon cycle models is important to reduce the uncertainties in global carbon cycle and climate projections. For this purpose, more evaluation and calibration of carbon models are required, using observation and long-term proxy-derived data. Centennial-length data could be obtained from tree-rings archives that provide long continuous series of forest growth changes with accurate annual resolution.

    Here we present results from a study conducted at Harvard Forest (Petersham, Massachusetts). The study examines the potential relationship between δ13C in dominant trees and GPP and/or NEE measured by flux towers. We have analysed the δ13C composition of wood-cellulose over the last 19 years from an eastern hemlock (Tsuga canadensis) and northern red oak (Quercus rubra) growing in the flux tower footprint. δ13C values show a decreasing trend of from 1992 to 2010. The decreasing values of δ13C are interpreted as a result of higher CO2 assimilation triggered by an increase of atmospheric CO2 concentration and the effect of N fertilization. This interpretation is in agreement with an observed increase in GPP and width, and strengthening of the carbon sink (more negative NEE). The tree-ring δ13C and GPP inter-annual variability are also highly correlated for the same period 1992-2006.

    Tree-ring width and δ13C results show the potential of these parameters as proxies for reconstructions of past CO2 assimilation and carbon sequestration by woody biomass beyond the time span covered by calibration data to the centennial time scales encompassed by tree ring records .

  • Research Category: Forest-Atmosphere Exchange