Background： The global network of eddy-covariance （EC） flux-towers has improved the understanding of the terrestrial carbon （C） cycle, however, the network has a relatively limited spatial extent compared to fore...Background： The global network of eddy-covariance （EC） flux-towers has improved the understanding of the terrestrial carbon （C） cycle, however, the network has a relatively limited spatial extent compared to forest inventory data and plots. Developing methods to use inventory-based and EC flux measurements together with modeling approaches is necessary evaluate forest C dynamics across broad spatial extents. Methods： Changes in C stock change （AC） were computed based on repeated measurements of forest inventory plots and compared with separate measurements of cumulative net ecosystem productivity （~NEP） over four years （2003 - 2006） for Douglas-fir （Pseudotsuga menzies# var menziesil} dominated regeneration （HDF00）, juvenile （HDF88 and HDF90） and near-rotation （DF49） aged stands （6, 18, 20, 57 years old in 2006, respectively） in coastal British Columbia. AC was determined from forest inventory plot data alone, and in a hybrid approach using inventory data along with litter fall data and published decay equations to determine the change in detrital pools. These AC-based estimates were then compared with Y_NEP measured at an eddy-covariance flux-tower （EC-flux） and modelled by the Carbon Budget Model - Canadian Forest Sector （CBM-CFS3） using historic forest inventory and forest disturbance data. Footprint analysis was used with remote sensing, soils and topography data to evaluate how well the inventory plots represented the range of stand conditions within the area of the flux-tower footprint and to spatially scale the plot data to the area of the EC-flux and model based estimates, Results： The closest convergence among methods was for the juvenile stands while the largest divergences were for the regenerating clearcut, followed by the near-rotation stand. At the regenerating clearcut, footprint weighting of CBM-CFS3 TNEP increased convergence with EC flux Z_NEP, but not for AC. While spatial scaling and footprint weighting did not increase convergence for AC, they did provide confidence that the sample plots represented site conditions as measured by the EC tower. Conclusions： Methods to use inventory and EC flux measurements together with modeling approaches are necessary to understand forest C dynamics across broad spatial extents. Each approach has advantages and limitations that need to be considered for investigations at varying spatial and temporal scales.展开更多
基金the Canadian Forest Service Pacific Forestry Centre Graduate Student Award, a CFCAS grant to the Canadian Carbon Program (CCP)Natural Sciences and Engineering Research Council of Canada (NSERC) Discovery Grant to NCCBenoit St-Onge of the University of Quebec at Montreal as part of an ongoing collaborative project with funds provided by NSERC and BIOCAP
文摘Background： The global network of eddy-covariance （EC） flux-towers has improved the understanding of the terrestrial carbon （C） cycle, however, the network has a relatively limited spatial extent compared to forest inventory data and plots. Developing methods to use inventory-based and EC flux measurements together with modeling approaches is necessary evaluate forest C dynamics across broad spatial extents. Methods： Changes in C stock change （AC） were computed based on repeated measurements of forest inventory plots and compared with separate measurements of cumulative net ecosystem productivity （~NEP） over four years （2003 - 2006） for Douglas-fir （Pseudotsuga menzies# var menziesil} dominated regeneration （HDF00）, juvenile （HDF88 and HDF90） and near-rotation （DF49） aged stands （6, 18, 20, 57 years old in 2006, respectively） in coastal British Columbia. AC was determined from forest inventory plot data alone, and in a hybrid approach using inventory data along with litter fall data and published decay equations to determine the change in detrital pools. These AC-based estimates were then compared with Y_NEP measured at an eddy-covariance flux-tower （EC-flux） and modelled by the Carbon Budget Model - Canadian Forest Sector （CBM-CFS3） using historic forest inventory and forest disturbance data. Footprint analysis was used with remote sensing, soils and topography data to evaluate how well the inventory plots represented the range of stand conditions within the area of the flux-tower footprint and to spatially scale the plot data to the area of the EC-flux and model based estimates, Results： The closest convergence among methods was for the juvenile stands while the largest divergences were for the regenerating clearcut, followed by the near-rotation stand. At the regenerating clearcut, footprint weighting of CBM-CFS3 TNEP increased convergence with EC flux Z_NEP, but not for AC. While spatial scaling and footprint weighting did not increase convergence for AC, they did provide confidence that the sample plots represented site conditions as measured by the EC tower. Conclusions： Methods to use inventory and EC flux measurements together with modeling approaches are necessary to understand forest C dynamics across broad spatial extents. Each approach has advantages and limitations that need to be considered for investigations at varying spatial and temporal scales.
