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Using inventory based field attributes to characterize carbon stocks and carbon stock changes within eddy-flux covariance tower footprints Ferster, Colin Jay

Abstract

Forests are an important part of the global carbon (C) cycle, and understanding and quantifying forest C dynamics is necessary for informed forest management decisions and accurate C budget accounting. This thesis contributes to the understanding of forest C dynamics by comparing biometric measurements of C stock changes (ΔC) and eddy covariance (EC) flux-tower measurements of cumulative net ecosystem productivity (ΣNEP) at three sites at the Fluxnet Canada Research Network British Columbia Flux Station; a young (near-end-of-rotation) forest established in 1949 (DF1949), a pole sapling stand established in 1988 (HDF1988), and a recent clearcut established in 2000 (HDF2000). To address spatial variability in stand and tower footprint conditions, first, light detection and ranging (lidar) remote sensing data were used to quantify large tree and snag aboveground mass (TSAM) at DF1949 (r²=0.75, SEE=29.68 Mg/ha). Next, for all three sites, remote sensing estimates were combined with advanced GIS data to estimate the spatial distribution of C stocks that are more difficult to measure directly using only remote sensing data. The resulting spatial representation of forest structure was combined with published EC flux-tower footprint probability distributions to enable a comparison between biometric ΔC stocks and tower ΣNEP. Where biometric ΔC stocks were difficult to resolve, changes were modeled using parameters from the Carbon Budget Model of the Canadian Forest Sector (CBM-CFS3). The best agreement between biometric ΔC stocks and tower ΣNEP was at DF1949 (mean = 15.18 ± 7.94 MgC/ha/4 years ΔC; 13.63 MgC/ha/4 years ΣNEP). The other two sites followed the same rank but had larger divergences and differences of sign (HDF1988: mean = 11.52 ± 1.17 MgC/ha/4 years ΔC and -1.93 MgC/ha/4 years ΣNEP; HDF2000: 3.59 ± 1.59 MgC/ha/4 years ΔC and -20.08 MgC/ha/4 years ΣNEP). An unaccounted source of respiration at the more recently disturbed sites may be related to stump, coarse root, and logging-slash decomposition. This study develops an approach and methodology that may be applied at other EC flux-tower sites where researchers wish to compare biometric-based measurements with micrometeorological-based measurements.

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Attribution-NonCommercial-NoDerivatives 4.0 International

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