Title: Use of Landsat-based monitoring of forest change to sample and assess the role of disturbance and regrowth in the carbon cycle at continental scales
Author: Cohen, Warren B.; Healey, Sean P.; Goward, Samuel; Moisen, Gretchen G.; Masek, Jeffrey G.; Kennedy, Robert E.; Powell, Scott L.; Huang, Chengquan; Thomas, Nancy; Schleeweis, Karen; Wulder, Michael A.
Source: In: Proceedings of the FORESTSAT 2007 Conference, 5-7 November 2007, Montpellier, France. CD. p. 14-19.
Description: The exchange of carbon between forests and the atmosphere is a function of forest type, climate, and disturbance history, with previous studies illustrating that forests play a key role in the terrestrial carbon cycle. The North American Carbon Program (NACP) has supported the acquisition of biennial Landsat image time-series for sample locations throughout much of North America for the purpose of characterizing carbon fluxes associated with forest dynamics. Disturbance events such as harvests or fires can release large amounts of forest carbon, whereas subsequent sequestration of carbon by forest regrowth can be a much slower process. We are using national forest inventory reference data in conjunction with the NACP Landsat time-series to model and map forest disturbance and recovery dynamics and related biomass changes over time. With our approach, forest changes associated with disturbance and regrowth can be summarized at the scene level, and the results from multiple scenes can contribute to estimates of disturbance-related carbon flux at national scales. In our case, the NACP Landsat scenes were chosen using a probability-based sampling framework that allows systematic weighting of scene-level results in the production of national estimates of disturbance-related carbon flux. Specific parameters that we are mapping and estimating include: annual area disturbed, total standing biomass removed through disturbance, and biomass gained through regrowth following disturbance. These efforts rely upon techniques that we developed to take full advantage of the temporal context provided by the NACP Landsat time-series. In particular, we fit non-linear functions to the temporal trajectory of each pixel to minimize noise and to identify genuine losses and gains of forest cover and related biomass. Our analyses address disturbance patterns going back to at least 1984, and as far back as 1972. The historical context emerging from these analyses is improving our understanding of the roles of forest management and climate on national- to continental-scale carbon cycles.
Keywords: image-time-series, change-detection, biomass, curve-fitting, large-area, spectral-temporal-trajectory
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Cohen, Warren B.; Healey, Sean P.; Goward, Samuel; Moisen, Gretchen G.; Masek, Jeffrey G.; Kennedy, Robert E.; Powell, Scott L.; Huang, Chengquan; Thomas, Nancy; Schleeweis, Karen; Wulder, Michael A. 2007. Use of Landsat-based monitoring of forest change to sample and assess the role of disturbance and regrowth in the carbon cycle at continental scales. In: Proceedings of the FORESTSAT 2007 Conference, 5-7 November 2007, Montpellier, France. CD. p. 14-19.
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