ForWarn Mean Summer National Difference Vegetation Index 2009-2013

The capacity of ecosystems to provide services such as carbon storage, clean water, and forest products is determined not only by variations in ecosystem properties across landscapes, but also by ecosystem dynamics over time. ForWarn is a system developed by the U.S. Forest Service to monitor vegetation change using satellite imagery for the continental United States. It provides near real-time change maps that are updated every eight days, and summaries of these data also provide long-term change maps from 2000 to the present.

Based on the detection of change in vegetation productivity, the ForWarn system monitors the effects of disturbances such as wildfires, insects, diseases, drought, and other effects of weather, as well as human-induced disturbances. This system also enables monitoring of post-disturbance recovery, the cumulative effects of multiple disturbances over time, and the effects of long-term forest growth. ForWarn consists of a set of inter-related products, including an archive of past change maps, seasonal vegetation phenology maps, and derived map products from these efforts. These products offer a window on large-scale landscape dynamics at high spatial resolution (230m), and are useful for a wide variety of conservation, natural resource management, and education applications.

Products highlighted include assessments of the degree of change in evergreen and deciduous plant productivity from 2000 to 2012. These “thrive” and “decline” maps are sensitive to one another (e.g., apparent loss in evergreen productivity can be driven by growth in deciduous productivity). In some regions, changes are driven by dramatic ecosystem-level processes, such as the loss of Hemlock trees due to the Hemlock wooly adelgid forest pathogen in the southern Appalachians. More basic measures of plant productivity within desired time periods are illustrated here by a 5-year map of the Normalized Difference Vegetation Index (NDVI). This index is related to important vegetation characteristics such as leaf area, biomass, and carbon storage.