Carbon Accumulation at the Harvard Forest: A Comparison of Methods for Measuring Tree Biomass for Regional Extrapolation of the Eddy-Flux Tower Footprint
Questions about regional carbon cycling dynamics are particularly important for northeastern forests because of their significance in the North American terrestrial carbon sink. The long-term study of CO2 exchange at Harvard Forest has been a key indicator of carbon uptake by northeastern forests, but establishment of the eddy-flux tower s relevance to the regional carbon budget requires scaling of the tower's CO2 flux measurements to the surrounding forested region. Acquisition of extensively placed variable-radius 'BigFoot' plots provided an opportunity to investigate the spatial representativeness of the tower flux data and of the associated fixed-radius plots in the tower footprint. The utility of the BigFoot data was first investigated through the comparison of the variable- and fixed-radius measurement methods. Stand measurements from the BigFoot plots were then compared with those from the tower footprint. Comparison of the different plot types indicates that variable-radius plots were not sufficiently accurate for forest carbon accounting. Fixed-radius measurement of the extensively placed BigFoot allowed them to be compared with the tower footprint. Results of this comparison show that the forest composition of the tower footprint is representative of the region, and thus that the tower effectively samples regional trends in carbon sequestration. Potential changes in land-use across the region highlight the need for additional measurements of extensively placed plots for validation of the tower as a representative site.