Droughts, Severe Winters And Pollution Don't Kil

DROUGHTS, WINTERS, AND POLLUTION DON'T KILL TREES IMMEDIATELY

Droughts, severe winters and air pollution may not cause obvious harm to trees until decades after these environmental stresses occur.

That's according to new research by Brian S. Pedersen, visiting assistant professor of biology at Roanoke College in Salem, Virginia, that punches holes in the theory that environmental events like droughts immediately lead to tree death.

He has authored two studies on the topic: "The Role of Stress in the Mortality of Midwestern Oaks as Indicated by Growth Prior to Death," accepted for publication in Ecology; and "Modeling Tree Mortality in Response to Short- and Long-Term Environmental Stresses," accepted for publication in Ecological Modeling.

"When trees die, people assume that it is because of current environmental stresses, such as a drought or unusually high air-pollution concentrations. My research suggests that trees often die as a result of environmental stresses that occurred decades before tree death," explains Pedersen.

Pedersen examined tree-ring growth data from 63 dead overstory oaks from seven Midwestern oak-hickory forests. The sites included: Touch-of-Nature Preserve and Dixon Springs Agricultural Station in Illinois; Clark State Forest and Deam Wilderness Area of the Hoosier National Forest in Indiana; and The Edge-of Appalachia Preserve and the Athens Unit of Wayne National Forest in Ohio, and Fly Gap Mountain, Arkansas.

Three-fourths of the dead trees had growth patterns prior to dying that included growth declines indicative of environmental stresses, such as a drought, that occurred decades before the trees died.

"For decades prior to their deaths, the now dead trees were growing significantly slower than comparable surviving trees," says Pedersen.

The results indicate that for oaks in the forests studied, tree mortality is usually a decades- long process involving a combination of environmental stresses. The results also suggest limits on using tree mortality as an indicator of a forest's response to specific environmental stresses. ###
Editors: If you wish to speak with Pedersen, you can reach him at 540-375-2445. His e-mail address is Internet: [email protected] Please contact Steve Infanti of Dick Jones Communications at 814-867-1963 if you would like copies of the studies. We help Roanoke College with some of its public affairs work.