Canadian Forest Service Publications
Comparison of carbon stock changes and cumulative carbon fluxes from inventory ground plots, eddy-covariance flux-towers and model estimates in an age sequence of coastal Douglas-fir stands in British Columbia. 2015. Ferster, C.J.; Trofymow, J.A.; Coops, N.C.; Chen, B.; Black T.A. Forest Ecosystems. 2:13.
Issued by: Pacific Forestry Centre
Catalog ID: 36207
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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 (ΔC) were computed based on repeated measurements of forest inventory plots and compared with separate measurements of cumulative net ecosystem productivity (ΣNEP) over four years (2003 – 2006) for Douglas-fir (Pseudotsuga menziesii var menziesii) 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. ΔC 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 ΔC-based estimates were then compared with ΣNEP 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 ΣNEP increased convergence with EC flux ΣNEP, but not for ΔC. While spatial scaling and footprint weighting did not increase convergence for ΔC, 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.
Plain Language Summary
Improved understanding of forest C dynamics across broader spatial scales requires development of ways to integrate C budget estimates from forest inventories, CO2 flux towers, and computer models. C stock changes (ΔC) were calculated from repeated measurements of forest inventory plots and compared with separate flux tower measurements and CBM-CFS3 model estimates of cumulative net ecosystem productivity (ΣNEP) over four years (2003 – 2006) for Douglas-fir 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. Convergence among methods was closest for juvenile, least for the regeneration, followed by the near-rotation stand. For regeneration, weighting for tower footprint area increased convergence of flux tower and model ΣNEP, but not for ΔC. While scaling and footprint weighting did not increase convergence for ΔC, its use increased confidence inventory plots better represented the tower site. However, challenges remain in making these comparisons because each method estimated C dynamics differently.