Scientific Consensus

From: Jennifer Tetterton <>
Date: Wednesday, April 14, 1999 2:03 PM
Subject: UPDATE: Air Pollution and Trees

Scientific Consensus on Air Pollution Impacts on Appalachian Forests


On March 26-27, 1999, fourteen scientists and experts with diverse specialties came together for a conference at Duke University's Nicholas School of the Environment, entitled "Acid Rain, Ozone and the Great Eastern Forests". They reviewed relevant literature, gave presentations of their own work, and engaged in scientific debate and discussion on the relationship between air pollution levels and the health of Appalachian forest ecosystems.  Their conclusions, based on consensus, were presented to the public on the second day and are summarized here.


Participating Scientists/Experts

John Bachmann, EPA
Robert I. Bruck, North Carolina State University
Wade Davidson, University of Kentucky
Frank Gilliam, Marshall University
William Grant, NASA
Jillian Gregg, EPA
Orie L. Loucks, Miami University
Steve McNalty, US Forest Service
Niki Nicholas, Tennessee Valley Authority
Ram Oren, Duke University
Dan Richter, Duke University
William Sharpe, Penn State University
William Smith, Wake Forest University
David Weinstein, Cornell University

*****Summary of Consensus Findings********

1)  Forest Effects of Soil Acidification

In the late 20th century, many Appalachian highland soils are progressively being acidified by atmospheric deposition and by the regional regrowth of the eastern forest.

Acid deposition contributes significantly to soil chemistry, and accumulated over decades, can both increase (nitrogen and sulfur) and decrease (nutrient cations)  the chemical elements in soils.

Soil acidification can be a predisposing stress contributing to the decline of forest plant species.

2)  Forest Effects of Ground-level Ozone ("smog")

Tree growth decreases under controlled ozone exposures for tree seedlings and saplings.

Ozone effects on trees are cumulative, thus exposures to even small concentrations can have an impact over time.

Reducing ozone levels to below ambient results in increased photosynthesis and growth in sensitive forest species.

The Appalachian forests will, most likely, change significantly if ozone levels remain the same, or increase.

3)  Forest Effects of Nitrogen Saturation

A continuum of nitrogen saturation exists in the landscape, and the southern Appalachians represent an area where many factors leading to saturation come together.

Nitrogen enrichment appears to inhibit winter hardiness for conifers and possibly for hardwoods.

Nitrogen saturation affects trees through relative reduction of fine roots, which makes trees more susceptible to short term drought.

Nitrogen saturation increases trees' susceptibility to insects/disease.

4)  Air Pollution Effects on Forest Diseases and Pests

Both acute and chronic episodes of acid deposition, ozone, and nitrogen can alter the incidence, epidemiology, and magnitude of tree insects and pathogens.

Experimental and field studies have shown insects and diseases can be proximal causes of forest decline but they are also as an outcome of precursor stresses, including atmospheric deposition.

Anthropogenic pollutant stress has been shown (in controlled experiments) to elicit plant biochemical and anatomical changes, leading to increased insect infestations and disease epidemics.

 5)  Summary Findings/Overview

Evidence exists that, for the high deposition regions of the Appalachians, acidification of the soils, ozone effects on trees, nitrogen enrichment, and potential insect and disease interactions with the above and other stressors, place the broadleaf ecosytems of the region on a path to change of probable public significance.

More research, including long-term field studies and modeling, is urgently needed to fully understand the interactions involved in forest decline in the Appalachians.

For supporting references, the complete findings, or a more official hard copy contact:

Jennifer Tetterton, Clean Air Organizer
Appalachian Voices, 703 W. King St., Suite 105, Boone NC 28607
phone (828) 262-1500;;

Jennifer Tetterton
Appalachian Voices
Professional Bldg.
703 W King St, Suite 105
Boone NC  28607
phone (828) 262-1500
fax (828)262-1540