Seeing Forest Stress from Drought in Real Time

RAFES tower at the Coweeta Hydrologic Laboratory in Otto, NC. Photo by Barry Clinton.

Most climate change models predict drier and warmer conditions across parts of the southern United States, which may translate into more frequent and severe drought events for those areas. With an estimated 60 percent of the drinking water of the South coming from forested watersheds—and many forests already stressed—land managers need to start planning now to offset the impacts of climate change.

It seems to make sense to start with the forests that are under the greatest stress at a given time, but up until recently it has been difficult to pinpoint exactly where these are until the damage has already been done. Traditional weather data on rainfall and temperature provide only a very general measure of the stress forest ecosystems may be experiencing.

A new resource, the Remote Assessment of Forest Ecosystem Stress (RAFES) network developed by SRS researchers at the Coweeta Hydrologic Laboratory (Coweeta), provides realtime data on climate impacts in at-risk forest ecosystems, giving managers the time they need to respond.

The researchers focused on water availability because of its importance in both regulating forest stress and streamflow. The system monitors levels of moisture-related stress by continuously sensing of soil water content and availability, soil temperature, woody fuel moisture and temperature, xylem sap flux density—correlating this information with weather information on precipitation, relative humidity, air temperature, and solar radiation.

Data from the sensed parameters are transmitted hourly to the NOAA Geostationary Operational Environmental Satellite (GOES), downloaded periodically, and archived for analysis.

RAFES stations are made up of solar-powered sensor arrays installed at multiple sites across the Eastern United States. Data from these sensors are transmitted in realtime to the GOES and can be retrieved from any location via the Internet. On select sites, data from the sensor arrays are linked with direct measures of tree water stress. Researchers are using these data to develop a PC-based analytical tool that allows managers to monitor and assess the severity of climate-related stress from sites on their own or comparable forests in realtime.

So far nine sites have been brought online in the RAFES network at locations that range from the Santee Experimental Forest on the South Carolina coast to the Crossett Experimental Forest in southern Arkansas and the Marcell Experimental Forest in northern Minnesota. RAFES sites span forest ecosystem types, land use histories, and hydrologic gradients. More are on the way for the Southern Appalachians and the Piedmont of the Carolinas.



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