Loss of eastern hemlock affects peak flows after extreme storm events

Aug 12, 2014

The 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 just published online in the journal Ecohydrology.

"Eastern hemlock trees have died throughout much of their range due to the , 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 processes such as ."

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."

Explore further: Fish will have to find new habitats or perish if global warming is left unchecked

More information: Ecohydrology, www.treesearch.fs.fed.us/pubs/46230

Related Stories

Loss of eastern hemlock will affect forest water use

May 09, 2013

The loss of eastern hemlock from forests in the Southern Appalachian region of the United States could permanently change the area's hydrologic cycle, reports a new study by U.S. Forest Service scientists at the Coweeta Hydrologic ...

Hemlocks still abundant despite adelgid infestations

Sep 26, 2011

A recent analysis of two decades of USDA Forest Service Forest Inventory and Analysis (FIA) data shows the live volume of hemlocks in the eastern United States still increasing despite spreading infestations ...

Recommended for you

Gimmicks and technology: California learns to save water

15 hours ago

Billboards and TV commercials, living room visits, guess-your-water-use booths, and awards for water stinginess—a wealthy swath of Orange County that once had one of the worst records for water conservation ...

Cities, regions call for 'robust' world climate pact

15 hours ago

Thousands of cities, provinces and states from around the world urged national governments on Thursday to deliver a "robust, binding, equitable and universal" planet-saving climate pact in December.

Will climate change put mussels off the menu?

15 hours ago

Climate change models predict that sea temperatures will rise significantly, including in the tropics. In these areas, rainfall is also predicted to increase, reducing the salt concentration of the surface ...

As nations dither, cities pick up climate slack

Jul 02, 2015

Their national governments hamstrung by domestic politics, stretched budgets and diplomatic inertia, many cities and provinces have taken a leading role—driven by necessity—in efforts to arrest galloping ...

User comments : 0

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.