National trends in ozone injury to forest plants: 16 years of biomonitoring

The ozone indicator, an important research component of the Forest Health Monitoring (FHM) Program of the Forest Service, U.S. Department of Agriculture, was developed and implemented to address specific concerns about the negative effects of ground-level ozone pollution on forest health and productivity. Ozone is a highly toxic air contaminant that has been shown repeatedly to damage tree growth and cause significant disturbance to forest ecosystems. Ozone also causes distinct foliar injury symptoms to certain species (bioindicator plants) that can be used to detect and monitor ozone stress (biomonitoring) in the forest environment.