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Harvard Forest Symposium Abstract 2005

  • Title: Carbon exchange studies at Harvard Forest using eddy flux tower measurements and ground-based ecological measurements
  • Primary Author: Christine Jones (Harvard University)
  • Additional Authors: Daniel Gonzalez-Kreisberg (Not Specified); Lucy Hutyra (Boston University); Kathryn McKain (Not Specified); J. William Munger (Harvard University); Elizabeth Hammond Pyle (Harvard University); Steven Wofsy (Harvard University)
  • Abstract:

    Carbon dynamics at Harvard Forest are measured using both eddy-flux measurements and ground based ecological measurements. The eddy flux tower at Harvard Forest was established in 1990 to continuously measure CO2 exchange. The tower measurements have shown an average uptake of 2.2 Mg-C ha-1 y-1 since 1992, with a range from 0.8 in 1998 to 4.2 in 2001. The flux measurements are continuing, but recent efforts have focused on linking the atmospheric measurements with processes on the ground, and with establishing the larger regional context for the local measurements. These results are highlighted here.


    In 1993, ecological plots (n=34, 10m radius) were established along radial transects in the upwind directions from the EMS tower. Initial measurements of tree diameters and number were made over the summer of 1993. The plots were resampled in 1998 to determine average above-ground woody increment, recruitment and mortality. Additionally, all trees greater than 10cm in diameter were outfitted with dendrometer bands for repeated measures of tree growth, and litter collections were also established. In 1999, five plots were added to the original three plots that were located on an actively managed forest, which was harvested in 2001. In 2001 these plots were expanded to 15m radius and trees > 5cm were banded along with litter collection.


    Gross carbon fluxes of live aboveground biomass in the EMS plots do not vary much year to year, ranging from about 1 MgC/ha to 1.63 McC/ha. The net flux of carbon from the live biomass shows more variation due to the differences in mortality. The years 1999 and 2002 in particular show the lowest accrual of net carbon (0.62, 0.33 MgC/ha) in the live biomass due to higher mortality rates (Fig 1). The harvested plots show a range of carbon accrual in the live biomass from 0.85 to 1.87 with net carbon fluxes getting larger each year following the harvest showing a strong growth rate in trees that remain post-harvest (Fig 2). Total leaf litter inputs in the EMS plots ranged from 1.25 MgC/ha to 1.47 MgC/ha with oak and maple accounting for 60-70% of the total leaf litter input from 1998 to 2003. The harvested plots show total leaf litter inputs ranging from 0.84 MgC/ha to 0.99 from 2000 to 2003. Oak accounts for more than 50% of the leaf litter inputs following the harvest in 2001while Maple inputs stay relatively constant.


    In the summer of 2004, we re-surveyed the Big Foot plots that had been established by in 2000 as part of larger MODIS validation study. The BigFoot plots cover a 25 km2 area around the EMS tower and provide a larger regional context of our ecological measurements. Because the Big Foot plot data was initially generated using a variable radius technique and EMS/Harvest Plot data is based on a fixed radius technique, a method comparison had to be made first. Preliminary comparisons of tower plots with extended Bigfoot plots indicates that standing biomass in plots falls with in the range of standing biomass in surrounding area but there appears to be a trend where fixed radius plots contain more biomass than variable radius plots (Figure 3), even when plots are located in the same place. Further evaluation of this disparity is ongoing and will be the focus of a senior thesis by K. McKain.

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