PDF Version of this ArticleForest Ecosystem Stress in Real time
by Zoë Hoyle
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| RAFES tower at the Coweeta Hydrologic Laboratory in Otto, NC. (photo by Barry Clinton, USDA Forest Service) |
Most climate change models predict drier and warmer conditions across the Southern United States, as well as other parts of the country, which may translate into more frequent and severe drought events. Drought not only impacts water supplies for humans but undermines the health of forest ecosystems by increasing susceptibility to insects, diseases, and wildfire. 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. A new resource, the Remote Assessment of Forest Ecosystem Stress (RAFES) network, developed by SRS researchers at the Coweeta Hydrologic Laboratory (Coweeta), will provide realtime data on climate impacts in at-risk forest ecosystems, giving managers the time they need to respond.
Traditional weather data on rainfall and temperature provide only a very general measure of the stress forest ecosystems may be experiencing.
"Current approaches are often conducted at too large a spatial scale, do not directly measure climate impacts on tree stress, and are not timely enough for managers to plan responses," says Barry Clinton, Coweeta research ecologist who's working on the RAFES project with research ecologist Chelcy Ford and project leader Jim Vose. "We're developing a fine-scale, realtime tree stress monitoring system that can be cost-effectively deployed across the landscape or strategically located in high-risk areas."
The researchers chose to focus on water availability as a stressor, considering its importance in regulating both forest stress and streamflow. The approach is to monitor levels of moisture-related stress through the continuous sensing of soil water content and availability, soil temperature, woody fuel moisture and temperature, xylem sap flux density—with precipitation, relative humidity, air temperature, and solar radiation as drivers. Data from the sensed parameters are transmitted hourly to the National Oceanic and Atmospheric Administration, 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 transmitted in real time to the GOES can be retrieved from any location via the Internet. On select sites, data from the sensor arrays are linked with direct measures of physiologically based indices 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 real time.
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 to the Marcell Experimental Forest in northern Minnesota. Other sites are located in the Southern Appalachians, the Piedmont and the coast of North Carolina. RAFES sites span forest ecosystem types, land use histories, and hydrologic gradients. More are on the way.
"The locations of the first sites reflect a combination of leveraging existing infrastructure and site access," says Clinton. "Our approach to adding additional sites will be to identify forest ecosystems that are particularly susceptible to climate change-related stress. Our goals are to be able to provide spatially and temporally explicit early warnings for managers, and in the bigger picture, to provide realtime information on ecosystem responses to extreme climatic events across representative at-risk forest types—as well as to validate conditions detected with coarser scale data such as satellite imagery."
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| Eddy covariance tower installed last year at Coweeta to measure the flow of carbon dioxide and other gases above the forest canopy. The observations made with this system, which is separate from the RAFES system, are critical for detecting variations in carbon and nutrient gases in relation to climate change. (photo by Zoë Hoyle, USDA Forest Service) |
The RAFES network fits nicely within the framework of current Forest Service efforts to evaluate direct and indirect effects of climate change on forest ecosystems and develop tools and practices for adaptation and mitigation. "This approach is the first attempt to our knowledge to quantify such spatially and temporally explicit stress conditions," says Clinton. "It could prove to be a valuable asset to forest management decisionmaking in the face of predicted climate change."
For more information:
Barry Clinton at 828–524–2128, x124 or bclinton@fs.fed.us
