September 3, 2009

Rhododendrons can be landslide hazards

The U.S. Forest Service says it's determined an expansion of rhododendron plants along Southern Appalachian slopes might increase the risk of landslides.

Scientists at the Forest Service's Southern Research Station in Atlanta said their findings suggest the expansion of rosebay rhododendron (Rhododendron maximum) in Southern Appalachian mountain hollows may increase the likelihood of landslides during and after intense rain events.

In an article recently published online in the journal Earth Surface, researchers Chelcy Ford and Jim Vose examined how the interaction between topography and the species of tree or shrub can affect the ability of soil to hold together.

We found that rhododendron had the shallowest, weakest roots suggesting that the recent expansion of this species may have lowered the cohesive strength of soil in some hollows, Vose, who led the study, said. Since debris flows usually start in the hollows, those dominated by rhododendron could represent a heightened hazard for landslides. Roots of trees and shrubs can represent up to 100 percent of what's holding soil together and keeping mountain slopes from sliding.

The researchers said although their study was not designed to firmly establish cause and effect, the results suggest rhododendron might be a key species affecting landslide initiation across the Southern Appalachians.

The study also included T.C. Hales and Larry Band of the University of North Carolina at Chapel Hill.