Ozone injury across the southern United States, 2002-06

Abstract

In the Eastern United States, hourly concentrations of ozone typically range from 30 to 50 parts per billion (ppb), with events that may exceed 100 ppb. Typical exposure levels can cause visible foliar injury to some plant species and have the potential to reduce tree growth by up to 10 percent per year, depending on species and environment. As part of the Forest Service, U.S. Department of Agriculture, Forest Inventory and Analysis (FIA) Program, ozone-induced foliar injury is evaluated in the South between late July and mid-August on about 350 ozone biosites. For 2002 through 2006, ozone injury occurred on between 8 (2006) and 29 percent (2003) of the sampled biosites. South Carolina had the highest percentage of biosites with injury in 3 out of 5 years. The area at greatest risk from ozone injury occurred in northern Georgia. Both the moisture index and the combination of ozone exposure and moisture were significantly different for biosites where injury was observed and biosites where injury was not observed. This evidence suggests that, despite reported declines in ambient ozone concentrations over the past 10 years, some forest areas in the South were classified in the low and no risk categories due to the moisture deficit conditions that existed during the 2002-06 time period. The correlation between ozone injury and moisture conditions, as well as the consistent low to moderate levels of injury, occurring year after year in some parts of the South, warrant continued monitoring and close scrutiny for potential forest health impacts. FIA conducts the only annual nationwide systematic survey for ozone-induced foliar injury. This information is extremely valuable to research on trends in ozone exposure and injury and the impacts to vegetation across the United States