US Forest Disturbance Rates Observed from Landsat

North American forests are thought to be a long-term sink for atmospheric carbon. However, great uncertainties exist in current understanding of the magnitude of this sink and its change in the foreseeable future, largely because forest disturbance and regrowth dynamics are not well characterized. A main goal of the North American Forest Dynamics (NAFD) project is to quantify US forest disturbance and regrowth by integrating forest inventory data and historical Landsat observations. From a total of more than 100,000 Landsat images in the USGS Landsat archive, we have selected the best 20,000+ images to construct annual time series datasets for the entire the conterminous US (CONUS) for the years from 1984 to 2011. These images have been converted surface reflectance to produce spatially and temporally consistent radiometry, and are being analyzed using the vegetation change tracker (VCT) algorithm to produce annual forest disturbance products. These products will be validated using design-based accuracy assessment methods, and the causing factor of each mapped disturbance event will be identified. In this talk, we will first provide an overview of the key NAFD methods and then present the preliminary results derived through the NAFD disturbance mapping effort, including initial quality assessment of the derived disturbance products, as well as patterns and rates of forest disturbances at national and regional scales. Issues, lessons learned, and future NAFD work will be discussed at the end.