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Northern Research Station
11 Campus Blvd., Suite 200
Newtown Square, PA 19073
(610) 557-4017
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  [photo] Composite photograph of ozone damage and data collection.

Ozone Biomonitoring Program


In 1994, the Forest Inventory and Analysis (FIA: and Forest Health Monitoring (FHM: programs of the USDA Forest Service implemented a national ozone biomonitoring program to demonstrate their commitment to sustainable forest management and The Montreal Process ( The ozone biomonitoring program uses ozone-sensitive plants to monitor air quality and the potential impacts of tropospheric ozone (smog) on our nation’s forests. This is the first nationally consistent effort to monitor ozone stress in natural systems. The field methods, sampling procedures, and analytical techniques have been approved by the scientific community.


What is ground level ozone?

Ground level ozone is considered the most pervasive air pollutant world-wide, and a serious threat to the conservation and sustainability of world forests. Ozone in the lower atmosphere is formed from the reactions of precursor pollutants, primarily nitrogen oxides (NOx) and volatile organic compounds (VOC’s) in the presence of sunlight. Automobile engines and industrial processes produce most of the compounds that result in ozone (O3) pollution. Ground level O3 is a major component of urban smog and part of the mix of greenhouse gases that contribute to global warming.

The airborne transport of O3 to remote forested areas has led to increasing concern about how this pollutant is influencing the health of individual trees and forest ecosystems. In the United States, periods of high ozone concentration coincide with the growing season when plants are most vulnerable to injury. Possible impacts of ozone on forest species include reduced growth and vigor, reduced seed production, and increased susceptibility to insects and disease. Long-term ozone stress may lead to changes in species composition, reduced species diversity, and simplification of ecosystem structure and function.

What is a bioindicator plant?

When ozone contaminates the environment, the bioindicator plant shows a visible response usually described as upper-leaf-surface ozone stipple for broad leaf plants, and chlorotic mottle for pine species. A useful bioindicator plant may be a tree, a woody shrub, or a non-woody herb species. The essential characteristic is that the species respond to ambient levels of ozone pollution with distinct visible foliar symptoms that are easy to diagnose.  Click on Ozone Sensitive Species on the right side of this page to check out the bioindicator species in your area.


What is ozone biomonitoring?

One way to monitor ozone air quality and potential impacts on our forests is to use bioindicator plants to detect and quantify elevated ozone concentrations in the forest environment. A nationwide network of over 1130 ozone biomonitoring sites has been established in forested areas in 45 states. Each year these sites are evaluated for the amount and severity of ozone injury on sensitive plants. The foliar injury data is used to quantify regional trends in ozone stress in terms of significant changes in the number and distribution of biomonitoring sites with ozone injury, and increases or decreases in injury severity. Results are interpolated across the landscape to predict where plant injury will occur, and identify areas of concern where growth effects studies are warranted.

Ozone biomonitoring and forest health assessment.

The findings of the national ozone biomonitoring program are used to address the following forest health assessment questions which are of interest to policy makers, forest land managers, the general public, and anyone else with an interest in maintaining sustainable forest management.

  1. Are phytotoxic (plant damaging) concentrations of ozone present in the forest ecosystem?
  2. Is regional air quality (e.g., ozone pollution) changing over time?
  3. If so, is it improving or deteriorating?
  4. In what percentage of a region or forest type is there an indication of ozone air quality impacts on scenic beauty as defined by measurable changes in leaf color, leaf size, or leaf number?
  5. In what percentage of a region or forest type is there an indication of ozone air quality impacts on ecological integrity as defined by measurable changes in biodiversity, growth increment, crown condition, or damage?



Last Modified: 08/21/2014