Tree shortage could affect peak flows in Appalachian watersheds after storm events

Sponsored by

Aug. 12, 2014 -- According to a new study conducted by U.S. Forest Service scientists at the Coweeta Hydrologic Laboratory (Coweeta) in the community of Otto, N.C., the loss of eastern hemlock -- a type of Pinaceae pine tree -- could affect water yield and storm flow from forest watersheds in the Southern Appalachians.

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.

"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."

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 and 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 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."

See also:

"MN develops first-of-its-kind stormwater management program using trees over pipes"

"Trees help Texas communities conserve water, energy"

###

Sponsored by

TODAY'S HEADLINES

IWW Adopts Executive Advisory Committee

As an editor, you hear mixed messages about an editorial advisory committee.

Kurita to acquire valuable ICL business units in asset purchase agreement

Kurita Water Industries and ICL have entered into an asset purchase agreement to allow Kurita to acquire ICL's Performance Products' aluminum, paper chemical and water treatment business units based in Ludwigshafen and Dusseldorf, Germany, as well as in Europe and China.

USDA announces $352M in funding to rehabilitate U.S. rural water systems

The USDA has announced that it is providing more than $352 million in loans and grants to rehabilitate rural water and wastewater systems nationwide as well as make infrastructure improvements in rural villages across the state of Alaska.

Thousands supporting clean water submit comments to EPA, USCE over 'Waters of the U.S.' definition

More than 700,000 Americans have written to support a plan to protect streams and wetlands nationwide that are vulnerable to pollution, and on a coalition of conservation organizations and clean water advocates have delivered their comments to the EPA and Army Corps of Engineers.

FOLLOW US ON SOCIAL MEDIA