Dr. James Steinman, a Research Forester with the USDA Forest Service, investigated the possibility that air pollution has led to mortality of larger trees in the Appalachian counties in Ohio, Pennsylvania, Kentucky, West Virginia, Virginia, Maryland, Tennessee, and Alabama. This geographic area offers a home to a great variety of tree species because of the unique combination of fertile soils and a warm, moist climate.

Speculation and accompanying publicity in some circles during the 1990’s was that acid deposition and ozone were predisposing trees to disease and causing accelerated mortality rates. These notions were based on observations confined to forest localities containing dead trees and with little regard for other causes of mortality.

Steinman dispels air pollutant theories by analyzing data collected from 5,404 random locations by the USDA Forest Service’s Forest Inventory and Analysis Program in the 1980’s. Comparisons of these data with those summarized in the 1940’s by the late ecologist, Dr. E. Lucy Braun, were also used to demonstrate that greater changes occurred in the forest during the mid-20th century before air pollution was considered a problem.

Dr. Steinman’s findings appear in the recent publication Changes in Composition of the Mixed Mesophytic Forest: Effects of Succession and Disturbance. Some of the highlights of this report are that:

• The mixture of larger trees in the 1980’s contained more pioneer species and less old-growth species than observed by Dr. Braun in the 1940’s. Most likely, major changes occurred when pioneer species invaded openings made by documented disturbances of logging, land clearing, fire, and chestnut blight in the mid-20th century.
• In the 1980’s, dead trees of pioneer species were more common than dead trees of old-growth species. This is expected considering that maturing trees of pioneer species are more sensitive to natural effects of shade, drought, and nutrient stress than trees of old-growth species.
• Overall, only six percent of all trees in the 1980’s were dead, which is an expected consequence of forest development. Tree death from competition for light, water, and nutrients and some loss from insects and disease is a part of the natural forest cycle.
• Species sensitive to air pollutants did not have percentages of dead trees that were significantly different from those that are not sensitive. These findings, coupled with stronger evidence of natural influences of forest development, do not support the possibility that air pollutants are causing accelerated tree mortality.
• Dead trees do not occur more frequently in geographic areas that are suspected of receiving higher amounts of air pollutants. Maps of these results provide further evidence that discount the effects of air pollution on tree mortality.

The USDA Forest Service is committed to continual monitoring and scientific reporting of the Mixed Mesophytic Forest. For more information, please contact Forest Service scientist Dr. James Steinman at (828) 259-0507. (Note: Dr. Steinman is now located at the Southern Research Station in Asheville, NC. He prepared his report for the Northeastern Area, State and Private Forestry while working in Radnor, Pennsylvania.)

State and Private Forestry is a branch of the USDA Forest Service that works in voluntary partnership with state agencies, landowners, and local governments. Technical and financial support is provided to improve the health, productivity and sustainability of state, municipal, tribal and nonindustrial private forestlands.

If you have questions about a forest pest call your local forester.