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Harvard Forest Symposium Abstract 2009

  • Title: Reducing uncertainty about the effects of climatic variation on forest ecosystems by measuring, modeling, and analyzing intermediate-turnover carbon pools
  • Primary Author: Andrew Richardson (Northern Arizona University)
  • Additional Authors: Bryan Dail (University of Maine); Eric Davidson (University of Maryland - Center for Environmental Science); David Hollinger (USDA Forest Service); J. William Munger (Harvard University); Paul Schaberg (USDA Forest Service); Steven Wofsy (Harvard University)
  • Abstract:

    Existing ecosystem models fail to predict measured year-to-year variation in forest carbon sequestration, limiting their value for predicting potential climate change effects. The primary objective of this NICCR-funded project is improved understanding of the causes of this variation in three important forest types of the NICCR NE Region, represented by the Howland (spruce-fir), Bartlett (beech-maple-birch) and Harvard (oak-hickory) AmeriFlux sites. New field measurements (quarterly estimates of temporal variation of stemwood non-structural carbohydrates [TNC], measured at all three sites, and transient C sinks and sources in the forest floor litter layer, evaluated with multi-year O horizon decomposition studies at Bartlett and Howland) and ongoing CO2 flux and ecosystem measurements are being used in conjunction with a minimally complex model of forest C cycling to address the role of these intermediate-term (months–years) dynamic carbon pools in regulating variation in C sequestration.

    In May 2007, transects were established in the tower footprint at each site, and 60 trees (20 trees for each of three species) were tagged, measured, and mapped for future TNC sampling efforts. Species were: red maple, red spruce, eastern hemlock (Howland), red maple, paper birch, American beech (Bartlett), and red maple, eastern hemlock, and red oak (Harvard). Every three months, one-half of the trees of each species at each site have been cored at breast height to a depth of 3 cm with an increment borer. Cores are put in plastic straws and frozen on dry ice in the field, and then shipped to the USDA Forest Service laboratory in Burlington, VT, for processing and analysis using standard methods. To date, we have collected samples in May 2007, August 2007, November 2007, March 2008, June 2008, August 2008, November 2008 and March 2009; samples from the first three collections have been fully analyzed. We observe large differences among species both in total TNC, and differences in how the TNC pool is partitioned to different compounds (starch, sucrose, glucose, fructose, raffinose, xylose and stachyose), but we are not yet able to detect strong seasonal patterns. Collection of cores for TNC analysis will to continue through August 2010.

  • Research Category: Ecological Informatics and Modelling, Forest-Atmosphere Exchange, Regional Studies