The Coweeta Hydrologic Laboratory

Part of the Coweeta basin, viewed from a lookout tower. Photo by U.S. Forest Service.

Much of what we know today about the hydrology of forested watersheds was learned through early research at the U.S. Forest Service Coweeta Hydrologic Laboratory (Coweeta).

Established in 1933 as the Coweeta Experimental Forest, the laboratory represents the longest continuous environmental study on any landscape in North America, as well as one of the oldest gauged watershed sites in the world.

Located in the Nantahala National Forest in western North Carolina, the 5,400-acre laboratory is made up of two adjacent, bowl-shaped basins covered with forest and containing several well-defined watersheds and over 45 miles of stream.

Coweeta scientists and partners continue to study the hydrologic cycle, but over the years their focus has expanded to include all components of the watershed ecosystem. The Coweeta basin serves as a living laboratory, where teams of scientists from many disciplines and locations study interactions among water, trees, soils, vegetation, and other organisms.

For over 75 years, the laboratory has provided scientists the opportunity to measure and record data on rainfall, evaporation, and streamflow. Using these data, Coweeta scientists have described the cycle and quality of water in an undisturbed forest, and studied the impacts of disturbances on water, nutrient, and organic matter cycles. Disturbances can come from nature itself—as insect infestations, tree diseases, droughts, or hurricanes—but they are more often the result of human activities. Climate change, air pollution, timber harvests, recreation, and development are examples.

Gauge house for one of the 32 weirs installed on Coweeta streams in the 1930s. Photo by U.S. Forest Service.

Forest scientists study the effect such disturbances have on the quantity, quality, and timing of water flow and on the associated components of the watershed ecosystem. Understanding the complex interconnections within watershed ecosystems requires skills from many areas of expertise.

Research at Coweeta ranges from molecular-level studies on genetic variability to large-scale analyses of land use change in the Southern Appalachian region. The current research program encompasses a broad array of cooperative studies, with an average of 30 projects a year involving approximately 50 senior investigators from universities and institutions from all over the world.

Over the past eight decades, the Coweeta research team has produced more than 2,000 research papers that have helped establish the foundation of knowledge required for the science-based management of natural resources.

The Coweeta LTER Program

Sponsored by the National Science Foundation (NSF), the Long-Term Ecological Research (LTER) program is a national network of 26 field research sites where more than 2000 scientists work cooperatively and across disciplines on long-term environmental research. Established in 1980 as one of six original LTER sites, the Coweeta LTER program is the centerpiece of long-term cooperation between the University of Georgia and the Coweeta Hydrologic Laboratory.

Since 1980, the program has evolved from a site-based to a region-based project. While much of the research is still focused on the Coweeta basin, research objectives have expanded to advance the scientific understanding of the spatial, temporal, and decision-making components behind the land use changes that have taken place in the Southern Appalachian region over the last 200 years—and to forecast patterns of change 30 years into the future.

For more information, email Chelcy Miniat at

The Southern Research Station is currently evaluating the role of our existing experimental forests in providing data and answers to the critical forest management questions identified in assessments such as the Southern Forest Futures Project, towards developing a functional experimental forest network that would also address the needs of our partners and publics. For more information, please visit: 

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SEEDS for the Future

Coweeta hosts ESA leadership meeting for diverse and talented ecology undergraduates

by Zoё Hoyle, SRS Science Communications
2016 SEEDS leadership students at Albert Mountain Fire Tower at the Coweeta Hydrologic Laboratory in Otto, North Carolina. Photo by Fred Abbott, ESA.

2016 SEEDS leadership students at Albert Mountain Fire Tower at the Coweeta Hydrologic Laboratory in Otto, North Carolina. Photo by Fred Abbott, ESA.

During April 13-16, 2016, scientists and staff at the U.S. Forest Service Coweeta Hydrologic Laboratory hosted the Strategies for Ecological Education and Diversity (SEEDS) 11th annual leadership meeting. An award-winning program of the Ecological Society of America (ESA), SEEDS focuses on students at the undergraduate level, with the mission to diversify and advance the ecology profession by stimulating and nurturing the interests of underrepresented students to participate and lead in the field of ecology.

This year’s meeting included 20 undergraduate students from a wide range of backgrounds and cultures, and focused on the theme “Diversity for Healthy Forest: the Connection between Forestry Science and Society.”

“This was an amazing opportunity, one that we were fully committed to from the moment we were asked to host the meeting and plan the agenda,” said Chelcy Miniat, project leader for the Forest Service Southern Research Station (SRS) Forest Watershed Science unit and the Coweeta laboratory. “The Forest Service Washington Office contributed funds to the meeting, and I worked with SEEDS staff and our scientists and staff to craft an agenda that addressed the meeting’s themes and introduced the students to careers in conservation and forestry available in the southern Appalachians.”

The agenda highlighted the ecology of the southern Appalachians and the importance of national forests in supplying fresh water supplies to the cities of the South. The Science Day on Thursday, April 14, featured onsite field tours to watershed experiments and weather stations, presentations on forestry experiments, the Migratory Bird Research Project – and later for fun, a night hike.

On Friday, the students engaged in a science communications workshop hosted by Babs McDonald, writer and editor for the Natural Inquirer, a middle science education journal published by the Forest Service. As part of the session, each of the students were asked to quickly read a scientific journal article by an SRS scientist and present an interesting talk about the article in two minutes. All of the students did an amazing job of communicating the main points of some very complicated research projects.

To help the students get an idea of the types of careers they might find in conservation and forestry in the southern Appalachians, the organizers put together a panel that included a national forest district ranger, Forest Service scientist, executive director of a local nongovernmental organization, timber manager for a local forest products company, science educator, and science writer. Lively discussions continued into lunch, which was prepared and served by the Forest Service Lyndon B. Johnson Job Corps Center based in nearby Franklin, North Carolina.

For more information, email Chelcy Miniat at

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Open or Shut: How Trees Respond to Drought at the Leaf Level

by Sarah Farmer, SRS Science Communications
Plants exchange water vapor and other gases such as oxygen through pores, or stomata, on their leaves. Photo by Annie Cavanagh, Wellcome Images, CC 2.0.

Plants exchange water vapor and other gases such as oxygen through pores, or stomata, on their leaves. Photo by Annie Cavanagh, Wellcome Images, CC 2.0.

Trees pull water into their roots, where some of it moves up the trunk against the pull of gravity. This upward movement, which is described by the cohesion-tension theory, is possible because of the chemical nature of water. Water molecules are attracted to each other (cohesion), so just before a water molecule evaporates from the leaf’s surface, it pulls (tension) another to the surface, and so on.

Although the surface of a leaf may look smooth, it is lined with tiny openings called stomata. When stomata are open, water vapor and other gases, such as oxygen, are released into the atmosphere through them.

A number of factors can affect the exchange of gases between a leaf and the atmosphere. U.S. Forest Service scientist Chelcy Miniat and her colleagues – including lead author Kimberly Novick, a researcher at Indiana University – recently modeled several of the factors that limit gas exchange. The scientists used tree sapflow data from a U.S. Forest Service monitoring network called Remote Assessment of Forest Ecosystem Stress (RAFES). Their study was published in the journal Plant, Cell and Environment.

Plants close stomata in response to their environment; for example, most plants close their stomata at night. Under drought, plants may also close their stomata to limit the amount of water that evaporates from their leaves. However, this strategy introduces new dilemmas. Because plants must exchange gases through their stomata, closing them prevents plants from taking up carbon dioxide (CO2). Without CO2, plants cannot make carbohydrates, and plants can only obtain this critical molecule when stomata are open. For plants, balancing the need to conserve water, especially in times of drought, with the need to take up carbon dioxide to support growth is a perpetual conundrum.

In general, plants have two options for balancing the need to take up CO2 with the need to conserve water. Some plants limit water loss by closing their stomata when conditions are unfavorable. For example, when the humidity is low, water is more likely to evaporate quickly from the leaf surface, and plants often close or partially close their stomata to maintain a stable water balance in the leaf. These species are called isohydric, and tend to do poorly during droughts, because without the gas exchange that open stomata allow, they cannot produce carbohydrates for survival. Instead, they rely on stored carbohydrates, and during long droughts these can be depleted and lead to tree mortality. Anisohydric plants keep their stomata open, even when facing water loss, but face significant risks should they run low on water; air bubbles can be pulled into their tissues, a potentially fatal situation.

Plants face several limitations when exchanging gases. In addition to the problem of losing water while obtaining carbon dioxide, water shortages could affect chemical processes – especially enzyme function within leaves. “We developed a new modeling framework linking leaf water loss and carbon gain,” says Miniat. “Our model shows where trees fall on the isohydric to anisohydric spectrum.”

Miniat and her colleagues compared several tree species from southwest Georgia to Arkansas, including white oak and loblolly pine. White oak is anisohydric, which means that it tends to keep its stomata open, even when conditions are harsh. Miniat and her colleagues showed that limitations in how effectively trees move water from their roots to their leaves helped them prevent the formation of potentially fatal air pockets in their tissues.

“Our study makes connections between the multiple obstacles plants face when exchanging gases with the atmosphere,” says Miniat. “We hope this model can inform ongoing efforts to explore how trees function during drought.”

Read the full text of the article.

For more information, email Chelcy Miniat at

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