The Santee Experimental Forest

On the South Carolina coast, heading off threats to water supply and quality

Carl Trettin explains long-term soil studies also installed on the Santee. Photo by Rodney Kindlund.
Carl Trettin explains long-term soil studies installed on the Santee. Photo by Rodney Kindlund.

In 1934, the U.S. Forest Service allocated 6,100 acres (2,470 ha) of the Francis Marion National Forest (Francis Marion) near Charleston, South Carolina, for the Santee Experimental Forest (the Santee).

By the 1930s, much of the site had been heavily used for centuries, the upland cleared to raise livestock and produce naval stores (tar, pitch, turpentine, and other products from pine), and rice and indigo were cultivated in the bottomlands. Between 1897 and 1929, the area was heavily logged. Early research on the Santee focused on thinning and fire management in loblolly pine stands.

Long-term environmental monitoring began in 1946 with the establishment of a weather station at the Santee headquarters. Then in the 1960s, in response to new concerns about the hydrologic impacts of a burgeoning timber industry, Forest Service researchers set up additional rain gauges and gauged weirs for streamflow on the Santee’s watersheds.

Four low-gradient gauged watersheds of different sizes ranging from 400 acres (160 ha) to 12,700 acres (5,140 ha), mostly on pine and hardwood mixed forest stands, were established. Researchers began observations in 1964, using the four watersheds to study soil moisture, evapotranspiration and runoff processes, as well as the effects of different types of land management practices including prescribed fire, thinning, and harvesting.

“In the mountains, water moves fast down steep slopes, but in low-gradient coastal areas, water moves in a slow, diffuse way,” says Carl Trettin, team leader for the SRS Center for Forested Wetlands Research based at the Santee. “In the Coastal Plain the riparian zone is much wider, so much more sediment is captured before it can enter the rivers. This also means there’s greater potential for mitigating nutrients such as nitrogen because the water is moving slow enough for the denitrifying bacteria to do their job and convert nitrogen to nitrogen gas.”

After 1982, there were no Forest Service hydrologists around to analyze and publish data from the hydro-meteorologic stations on the Santee. Fortunately, technicians on the site recognized the importance of the data and steadily kept records over the years (except from 1982 until Hurricane Hugo in 1989, which devastated most of the forest) from weirs, weather stations, and groundwater wells, storing them in whatever format was available at the time—tape, floppy discs, and often on paper.

The Santee unit finally got another research hydrologist, Devendra Amatya, in 2002. By that time, urban development in the greater Charleston area was fast encroaching on the Francis Marion, pushing stormwater management and water quality issues to the forefront. In 2004, Amatya started a research initiative focused on the Turkey Creek watershed in the Francis Marion with partners from colleges and universities, private industries, and State and Federal agencies joining SRS scientists in studies of the urbanizing landscape in relation to water quality and quantity and other related ecosystem services.

Findings from the Santee have shown that 75 to 80 percent of the area’s annual precipitation is lost to evapotranspiration from coastal forests, which commonly results in moisture deficits causing streamflow to be ephemeral. However, the areas typified by the Santee also have a shallow water table throughout the year, so that during large storms runoff can be significant.

The long-term monitoring at the Santee is particularly important for assessing extreme events. For example, following Hurricane Hugo, the streamflow pattern of the paired watershed reversed, and then returned to the pre-Hugo pattern by 2004, demonstrating the functional linkage between streamflow and forest condition.

“Another example was the recent extreme event on October 3rd and 4th, 2015, when we had 48 hours rainfall exceeding nearly 20 inches, which produced runoff that exceeded the carrying capacity of the gauging stations,” said Amatya. “This let us know that we probably need to reassess the capacity of the gauging stations, since climate change models project more frequent storms for the region in the future.”

New studies on the Santee in collaboration with investigators from Clemson University look at the effects of prescribed fire on water quality, specifically addressing whether runoff from burned areas affects the treatability of surface water for domestic use.

Whether addressing the effects of extreme climate events or the effects of land management, the long-term monitoring infrastructure at the Santee is fundamental to providing the data needed to produce the tools and information for effective land management for future Coastal Plains forests.

For more information, email Carl Trettin at ctrettin@fs.fed.us or Devendra Amatya at  damatya@fs.fed.us.

SRS maintains 19 experimental forests located on National Forest System lands and uses these sites for long-term and contemporary research on water, climate, and forest resources. SRS is currently working with research partners to develop a framework for networking these 19 forests, in order to answer the critical science questions of the 21st century. Click here for more information.

 

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