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Harvard Forest Symposium Abstract 2010

  • Title: Sources of uncertainty in estimating regional above ground biomass and potential carbon storage
  • Primary Author: Julian Jenkins (University of New Hampshire - Main Campus)
  • Additional Authors: Mary Martin (University of New Hampshire - Main Campus); Scott Ollinger (University of New Hampshire - Main Campus)
  • Abstract:

    Accurate assessment of carbon sequestration potential in northeastern U.S. forests is important for coupled climate-ecosystem research and is necessary for implementation of climate mitigation policies. Estimation of potential carbon sinks in forests requires accurate data for at least two important variables: (1) the size of present-day biomass pools, and (2) an understanding of the maximum biomass forests could attain if allowed to reach steady state. While there is some uncertainty in the application of forest inventory data, much larger uncertainties exist in the prediction of maximum potential biomass. In particular, limited data for old-growth forests makes validation of modeled growth rates difficult and current wood turnover estimates are similarly based on sparse measurements. At Hubbard Brook Experimental Forest, for example, measured aboveground biomass stabilized earlier and more abruptly than anticipated (Siccama et al. 2007). In contrast, carbon accumulation in similar aged forests at Harvard Forest has been increasing (Urbansky et al. 2007), despite widely held theories that predict the opposite pattern.

    We have conducted a preliminary analysis of forest carbon storage potential for all states participating in the Regional Greenhouse Gas Initiative (RGGI) using USDA FIA data to calculate current above ground stocks and the PnET-CN terrestrial ecosystem model to estimate the maximum biomass. In some cases, results were as expected: More rural counties in the western and northern parts of the region show the largest predicted C sink potential (currently at between 50-75% of their estimated storage potential). This is likely because forests in these areas are typically younger as a result of more active harvesting. However, some areas show far less storage potential than one would reasonably expect, particularly the central counties of Massachusetts where Harvard Forest is located at an estimated 95% of potential. Considerably different species mixtures (derived from FIA) verses adjacent counties in Connecticut are partially responsible for this. But the annual woody loss rate used in estimating biomass from the model is also a significant uncertainty in this result. For example, a wood turnover rate of 2.0% vs. 2.5% will result in a 20% increase in predicted maximum above-ground biomass.

    As we continue this regional analysis of sequestration potential, we will incorporate estimates of historical O3 pollution, land-management, N deposition along with variability in soil water holding capacity and predictions of elevated CO2 concentration. We will refine estimates of wood turnover and dead wood decay using newly available datasets and validate modeled biomass increment using age-classed data from specific research forests and the regional FIA database.

  • Research Category: Regional Studies