How Green is a Healthy Forest?

Researchers have introduced  new ForWarn map products to better monitor forest disturbances when year-to-year climate variation interferes with disturbance detection. This ForWarn image from July 11, 2013 shows an ongoing gypsy moth defoliation across western New York and Pennsylvania. Image by U.S. Forest Service.
Researchers have introduced new ForWarn map products to better monitor forest disturbances when year-to-year climate variation interferes with disturbance detection. This ForWarn image from July 11, 2013 shows an ongoing gypsy moth defoliation across western New York and Pennsylvania. Image by U.S. Forest Service.

As new spring leaves emerged and a wave of green moved up through the United States, the 2013 growing season began—and U.S. Forest Service researchers were watching. In forests, greenness levels change with natural rhythms called phenology, including seasonal changes, growth and mortality, year-to-year climate variation, and effects of disturbance. All of these indicators are important to forest health.

To help managers of federal, state, and private lands monitor this greenness, Eastern Forest Environmental Threat Assessment Center scientists, working with federal and university partners, developed the ForWarn system. ForWarn includes a web-based tool, the Forest Change Assessment Viewer, which distributes weekly maps of forest greenness levels from coast to coast. The maps are based on satellite imagery, and provide important information about the health and development of current forest phenology compared to the previous year, the last three years, and the past decade. Depending on how current greenness levels may differ from “normal,” expected conditions for a particular location and day of year, researchers and managers may be alerted to sudden disturbance events, slow-acting disturbances, or even successful forest recovery.

ForWarn provides a variety of supporting information and products that can help users take a closer look at unusual conditions in order to identify and track possible causes of disturbance, such as insects, diseases, wildfires, extreme weather, and more. With the ability to conduct preliminary assessments from any computer with a standard internet browser, ForWarn users can direct attention and resources to areas requiring on-the-ground investigation, potentially saving significant time and money.

Several new ForWarn features have been added for the 2013 growing season to aid researchers and managers with forest monitoring, including:

  • Flexible map delivery: A new version of the ForWarn Forest Change Assessment Viewer allows users to view and share the weekly maps and offers improved map access on mobile devices and portable computing tablets such as smartphones and iPads.
  • Rapid disturbance detection: A new map series, called Early Detect, provides faster initial images of new potential forest disturbances. ForWarn users can view Early Detect maps first, to check for the earliest indications of new disturbances, before consulting the standard ForWarn maps and supporting information.
  • Improved disturbance detections in years with early or late seasonal development: Two new ForWarn map products show current phenology compared to “average” greenness levels for any given location and day of year. These maps can improve detections of potential forest disturbances in spite of year-to-year differences in the onset of spring and fall seasons.
  • Retroactive forest monitoring: ForWarn has been operating since 2010 based on satellite imagery dating back to 2000. Users can now go “back in time” to view pre-2010 maps of known disturbances to assist with recognition and identification of current (and future) forest disturbance events and causes.

As managers use new ForWarn features to monitor forest phenology, they will better connect to natural vegetation rhythms and greenness associated with forest health. “The new viewer and map products we’ve added to the toolbox should complement the existing ForWarn products nicely,” says Bill Hargrove, Eastern Threat Center research ecologist and lead ForWarn researcher located in Asheville, North Carolina.  “These new features will provide forest owners and resource managers with the ability to recognize, identify, and react to forest disturbances faster and more easily than ever before.”

For more information, email William Hargrove at whargrove@fs.fed.us.

 Access the latest publications by SRS scientists.

Subscribe to our newsletter!

Receive weekly updates