Changes at Streamside in the Southern Appalachians

Loss of eastern hemlock affects peak flows after extreme storm events

by Zoё Hoyle, SRS Science Delivery Group

08.19.HWApneedles1The loss of eastern hemlock could affect water yield and storm flow from forest watersheds in the southern Appalachians, according to a new study by U.S. Forest Service scientists at the Coweeta Hydrologic Laboratory (Coweeta) located in Otto, North Carolina. The article was recently published online in the journal Ecohydrology.

“Eastern hemlock trees have died throughout much of their range due to the hemlock woolly adelgid, an exotic invasive insect,” said Steven Brantley, a post-doctoral researcher at Coweeta and lead author of the paper. “Though this insect has decimated whole stands of eastern hemlock along streams in the southern Appalachians, few studies have addressed the effects of this insect outbreak on landscape-level watershed processes such as stream flow.”

Because of its dense evergreen foliage, eastern hemlock plays an important role in the water cycle of southern Appalachian forests, regulating stream flow year round. Although eastern hemlock rarely dominates the region’s forests, the tree is considered a foundation species in the streamside areas called riparian zones.

Previous research by the Coweeta scientists led them to suspect that the loss of eastern hemlock would cause stream flow to increase over the short-term, especially in the dormant fall/winter season, then decrease over the longer term, with small effects annually. They also thought that peak flows after storms would increase, especially in the dormant season.

For this study, Coweeta researchers used a paired watershed approach—one watershed with a major hemlock component in the riparian forest area, the other reference watershed with very little—to determine the effects of hemlock mortality on stream flow and peak flow following storms.

Since hemlock woolly adelgid was first detected in 2003, all the eastern hemlock trees in both watersheds died, resulting in a loss of 26 percent of forest basal area (that area occupied by tree trunks and stems) in the riparian area of the first watershed compared to a 4 percent loss in the reference watershed riparian forest.

“Instead of finding that stream flow increased after hemlock mortality, we found no real change in any year after infestation,” said Brantley. “We did find, however, that peak stream flow after the largest storm events increased by more than 20 percent.”

“The fact that hemlock loss didn’t increase water yield in the short-term was due to the rapid growth response of co-occurring trees and shrubs in the riparian forests, and peak flows were likely higher after hemlock loss due to lower interception by the evergreen canopy in the riparian zone,” said Brantley. “This latter finding suggests that riparian trees may play a disproportionally important role in regulating watershed processes than trees that aren’t adjacent to the riparian zone.”

“It also has implications for the more extreme rain events predicted under climate change,” he added. “Losing foundation species in forested riparian zones could amplify the effects of altered precipitation regimes.”

Read the full text of the article.

For more information, email Chelcy Miniat at

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Posted in Experimental Forests, Forest Watersheds, Insects and Diseases, Threats, Upland Hardwoods

Life on the Forest Floor: Woodland Herbs of Southern Appalachian Cove Forests

by Sarah Farmer, Science Delivery Group
Cove forest near Coweeta Hydrologic Laboratory. Photo by Paul Bolstad, courtesy of

Acidic cove forest (note rhododendron midstory) near Coweeta Hydrologic Laboratory. Photo by Paul Bolstad, courtesy of

Cove forests in the Southern Appalachians may be carpeted with lush herbaceous understories of ferns, flowers, and other plants without woody stems.  Or they might have extremely sparse understories, with a dense midstory of rhododendron. “Both cove types are moist areas with dense tree canopies, as well as similar landform, geology, and topography, says U.S. Forest Service Southern Research Station (SRS) scientist Katherine Elliott. Elliott is a research ecologist at the SRS Coweeta Hydrologic Laboratory and lead author of a new synthesis paper about woodland herb communities in cove forests. The paper was recently published in the Journal of the Torrey Botanical Society.

The amount of light reaching the forest floor is the main difference between the two types of coves, although they also differ in the fertility and acidity of the soil. In acidic coves, thick evergreen midstories block most of the sunlight before it reaches the forest floor. In rich coves (no rhododendron midstory and understory species richness), the midstory is open and woodland herbs such at trilliums and ferns thrive below the tree canopies.

When trees die or fall over, or when other disturbances cause more light to reach the forest floor, plant diversity may increase. “One of the things our synthesis study showed is that some diversity and richness measures may be inadequate or misleading when applied to rich coves,” says Elliott. Increases in diversity after disturbance could reflect colonization by early-seral species, rather than the ginseng, black cohosh, trilliums, ferns, Jack in the pulpit, and many other species that indicate rich cove forests.

Elliott and her colleagues identified a number of additional gaps in the understanding of cove forests. The life history and physiology of many woodland herbs is poorly understood, and although researchers are starting to learn how drought, pests, pathogens, and climate change could affect forest trees, the effect these same stressors will have on herbaceous communities is unknown. “Much attention has been given to logging and its effects on richness and diversity in woodland herb communities,” says Elliott. “However, other stressors may be equally or even more important to consider in the future.”

In addition to synthesizing existing literature, researchers analyzed original data collected in rich cove forests within the Coweeta Basin of western North Carolina, and compared species diversity and richness among watersheds with different land uses and disturbance histories. The Coweeta Basin includes managed and unmanaged watersheds, and has been part of the SRS Coweeta Hydrologic Laboratory since 1934.

The synthesis revealed that no single study or dataset could provide specific management strategies. “The overriding conclusion of our synthesis,” says Elliott, “is that restoring herbaceous communities requires action proportional to the severity of past disturbance, as well as the current condition, stressors, and site characteristics.”

Read the full text of the article .

For more information, email Katherine Elliott at

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Posted in Uncategorized

The Interaction of Climate Change, Fire, and Forests in the U.S.

Special Journal Section Provides Regional Assessments

Smoke from large Arizona wildfire during 2013 fire season. Photo by U.S. Forest Service.

Smoke from large Arizona wildfire during 2013 fire season. Photo by U.S. Forest Service.

A special section of the September issue of Forest Ecology and Management, available online now, assesses the interactions among fire, climate change, and forests for five major regions of the United States.

The editors of the section—Chelcy Miniat from the U.S. Forest Service, Monique Rocca from Colorado State University, and Robert Mitchell (now deceased) from the Joseph W. Jones Ecological Research Center—started the project by organizing teams of scientists from the Forest Service and universities to provide scientific input into the third National Climate Assessment (NCA), which is prepared at least every four years to assess the effects of climate change on sectors, resources, and regions of the United States.

“The idea for the section came from conversations I had with Bob Mitchell when I was working with the U.S. Global Change Research Program a few years ago,” said Miniat, project leader with the Forest Service Southern Research Station. “We quickly realized that the ability to manage wildfires and to use fire as a tool would be affected by climate change and that this interaction needed more attention in the next round of assessments. We wanted to tailor this information for forest managers.” Miniat and fellow authors describe the process and findings in the section’s introduction.

Articles in the special section review the interactions between climate and fire in five different regions of the U.S—the Pacific Northwest, Southwest, Rocky Mountains, mid-Atlantic, and Southeast. Each article follows the same general structure, providing a description of the region and its forest types; discussion of projected changes in climate and how they will likely impact fire and forests; and a synthesis of what is known about the effects of fire on forest ecosystem services such as water quantity and quality, air quality, and biodiversity.

“The growing interest in fire and climate has been fueled by numerous predictions that wildfires—especially in the West—will get larger, more intense, and increasingly hard to contain with climate change,” said Rocca. “Understanding the complex relationships among climate, fire, and vegetation is critical to the ability of policymakers and resource managers to respond to climate change. Our goal in these articles is not only to provide the best available science, but also to inform the conversation on how forest management choices can impact the valuable services we derive from our forests.”

Read the article by SRS scientists about the future of climate and fire interactions in the Southeast.

For more information, email Chelcy Miniat at

Access the latest publications by SRS scientists.

Posted in Climate Change, Fire