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Northern Research Station
One Gifford Pinchot Drive
Madison, WI 53726
(608) 231-9318
(608) 231-9544 TTY/TDD




The sampling rules for the ozone biomonitoring sites are as follows.

  • Biosites are wide-open areas, at least one acre in size, within or alongside forested areas.
  • Each site contains at least 30 individual plants of at least two bioindicator species. The eastern and western FIA regions average 3.5 and 2.5 species per biosite, respectively.
  • Access to the biosite locations must be easy, and they must be free of significant soil compaction and other man-made disturbance.  
  • Up to 30 plants of each species are randomly selected for injury evaluation. Plants less than 12 inches in height, suppressed, shaded, or with more than half the crown out of reach are not evaluated.
  • Each plant is rated for the proportion of leaves with ozone injury (injury amount) and the mean severity of symptoms (injury severity) using a modified Horsfall-Barratt scale with breakpoints at 0, 6, 25, 50, 75, and 100 percent.
  • Voucher leaf samples (three leaves of each injured species evaluated at each location) are collected to provide the necessary validation of the ozone injury symptom observed in the field by the field crews.  One expert reviews all of the vouchers for eastern bioindicator species, and a second expert reviews all of the western bioindicator species.


The training and quality assurance procedures are as follows.

  • Just prior to the sampling window, ozone training and certification sessions are held in each FIA region. All crews receive training in bioindicator species identification, site selection procedures, ozone injury evaluations, and voucher handling.
  • Experienced and certified QA crews conduct audits and re-measurement activities. Blind checks are conducted on a minimum of 10 biosites in each FIA region. End-point data quality goals are also set for the calculated plot-level injury index, and the leaf voucher data.
  • Field data are collected electronically on a portable data recorder (PDR) and subject to a computerized editing and validation process. Paper data sheets are used to map the biosite and track the leaf vouchers, and for backup in the event of a PDR failure.
  • The crew level of difficulty for the ozone indicator is low and no specialized equipment is needed. The sampling window is abbreviated within each region, minimizing index-period variability. The selected bioindicator species are relatively common, easy to identify, and characteristically ozone sensitive, showing foliar symptoms that are easy to diagnose. Performance evaluations demonstrate that crews are effectively trained to detect ozone injury and discriminate against mimicking symptoms.


Additional details on field methods and QA procedures are available on-line. click on “FIA Library” and “Field Guides, Methods and Procedures”



Last Modified: 04/17/2007