Understanding the Ozone Indicator

• Why do we care about ozone and forest health?

• What is biomonitoring?

• Why is it important? Who uses the data?

• What are the field procedures?

• How is the data summarized and reported?

Ozone Injures Trees

Ponderosa pine stand Paul Miller and crew

1. More than 35 tree species have been identified as ozone sensitive based on foliar injury symptoms.

Ponderosa pine - CA

ozone sensitive black cherry in Vermont

2. In the field, symptoms are prevalent both on young trees and in the canopies of mature trees.

ozone sensitive aspen clone

3. Ozone can affect the genetic base of sensitive species through the elimination of sensitive clones and hypersensitive genotypes.

4. Ozone can reduce carbon fixation, increase foliar and root respiration, shift the partitioning of carbon into different chemical forms and disrupt carbon and nutrient allocation patterns.

Full crown on black cherry and, same tree, showing ozone-induced premature

defoliation later on in the growing season (Pennsylvania).

5. Small decreases in net photosynthesis or other growth-related processes compounded over the long life span of a tree may produce significant growth reductions or translate into large changes in stand dynamics, even if effects go undetected in the short-term due to the inherent complexity and variability of natural systems.

6. In the mixed conifer type in southern California, the elimination of ozone sensitive pines has led to an increase in ozone tolerant species characterized by thinner bark and branches close to the ground. This, in turn, presents a fuel ladder situation that jeopardizes the residual stand in the event of a catastrophic fire.

Tree ecosystem effect

What is Biomonitoring?

Ozone sensitive plants (bioindicators) act as detectors of ozone pollution. Detection is based on a visible foliar response that is produced as ozone enters plant leaves through open stomates during the normal process of gas exchange. Once inside the leaf, ozone changes membrane permeability leading to cell death and the appearance of characteristic symptoms on the leaf surface.

Chlorotic mottle on ponderosa pine; classic ozone stipple on sassafras; and premature fall coloration on sweetgum.

Bioindication

Ozone bioindicators provide evidence of plant stress. They tell us not only that ozone concentrations were elevated for a particular time and place, but also that other necessary conditions for ozone uptake and injury (e.g., adequate light, nutrition, and moisture) were also present.

In this context, the foliar response of ozone bioindicator plants is used to determine the presence or absence of ozone injury conditions on the biomonitoring plots.

Biomonitoring

A quantitative assessment of bioindicator response is provided by the plot-level ozone injury index (biosite index). The index is formulated from the injury amount and severity ratings recorded for each plant and the numbers of plants and species evaluated at each site.

The biosite index is not intended to beused as a measurement of harm. Rather,it provides a relative value, a gradationof response that quantifies the degree ofozone injury conditions on the biomonitoring plots.

Biomonitoring and Forest Health Assessment

1. Are phytotoxic concentrations of ozone present in the forest ecosystem?

2. Is regional air quality (specifically ozone pollution) changing over time? If so, is it increasing or decreasing?

3. In what percentage of a region or forest type are ozone bioindicator plants indicating the possibility of air pollution impacts on forest growth and condition?

Why is the ozone indicator important?

• TO MEET USFS INITIATIVES

The Montreal Process: The USDA Forest Service made a commitment to monitor the area and percent of forest land subjected to levels of specific air pollutants, including ozone, which may cause negative impacts on the forest ecosystem.

Biomonitoring is a proven technique for the detection of plant damaging concentrations of ozone in the natural environment.

Why is the ozone indicator important?

• TO SUPPORT NATIONAL POLICY ON PLANT HEALTH PROTECTION

There is a recognized need for biological data that can help inform and influence the establishment of meaningful air quality standards to protect plants from ozone damage.

The scientific community says foliar injury data from natural systems is a priority research need.

FIA biomonitoring meets that need.

Ref.: The need for a long-term cumulative secondary ozone standard - an ecological perspective. W.W.Heck and E.B.Cowling. NCSU

Why is the ozone indicator important?

• TO IMPROVE FOREST HEALTH MODELS

Model simulations are the only way we can get close to interpreting the risks associated with long-term ozone exposures.

Biomonitoring data provides more, different, and better data that will improve the reliability of forest health models.

Ref.: Risk characterization of tropospheric ozone to forests. W.E. Hogsett, A.A. Herstrom, J.A. Laurence, E.H. Lee, J.E. Weber, and D.T. Tingey

What are the field procedures?

Step 1: The field crew selects a suitable site for biomonitoring.

• Biomonitoring plots are wide open areas, at least 1 acre in size, alongside forested areas.

• Biomonitoring plots must contain at least 30 individual plants of at least 2 bioindicator species.

There is a requirement for 1 plot per polygon on the national ozone grid. Grid documents are available on the FIA web site.

Step 2: The location of the biomonitoring site is mapped, geographic coordinates are recorded, and standard codes are used to describe plot size, elevation, terrain position, aspect, soil drainage, soil depth and disturbance.

western biomonitoring site

Step 3: The field crew identifies 3 or more known ozone sensitive species at the site for injury evaluations.

Plant locations are mapped (approximately) so that the same population of plants is evaluated at every plot visit.

eastern biomonitoring sites

Step 4: Thirty individual plants of each species are rated for the percent of the plant that is injured and the average severity of injury on a 5-point scale.

Code Scale

0 No injury

1 1-6%

2 7-25%

3 26-50%

4 51-75%

5 >75%Ref.: Horsfall and Barratt. An improved grading system for measuring plant disease.

Step 5. The field crew collects a voucher sample (pressed leaves with ozone injury symptoms) for each injured species and returns it to the regional expert for validation of the ozone injury symptom.

Western expert: Pat Temple

Eastern expert: Gretchen Smith

Step 6. The same sites and the same approximate population of plants are evaluated every year.

The goal is to provide a biological index of ozone stress in the forest environment using a consistent protocol on a nation-wide system of biomonitoring plots.

Results from the national grid are used to quantify regional trends in ozone stress in terms of significant changes in the number and distribution of biomonitoring plots with ozone injury and increases and decreases in the injury severity index.

The index will be used to create a spatial response surface such that index values can be predicted for all P2 and P3 plot locations.

What happens to the biomonitoring data?

Reporting

We report on regional and national trends in ozone injury to plants.

We predict where ozone injury will occur.

We identify problem areas where growth effects studies are warranted.

Principal Analysts: Bill Smith and John Coulston, along with Teague Prichard, Ed Jepsen, Jim Steinman, and Ken Stolte.

Study objective: To examine trends and percent forest subjected to specific levels of air pollution, and summarize results by Resource Planning Act reporting region.

Results: Ozone stress characterized in terms of ozone-induced foliar injury to sensitive species was recorded in only a small percentage of forested areas across all RPA regions.

A preliminary assessment of the Montreal Process Indicators of Air Pollution for the United States. John W. Coulston, Kurt H. Riitters, and Gretchen C. Smith.

South Carolina: Relationship between ozone exposures and ozone biomonitoring plots. [Draft Image] Source: Teague Prichard – WI DNR

Examples of summary statistics for the ozone indicator

South Carolina [draft]

FIA analysts should use consecutive 5-year periods with variable ozone levels, weather, wind flow, and precipitation patterns to examine regional trends in ozone air quality over the long-term.

Core Figure: Ozone Biomonitoring Index

Biosite Value Bioindicator response Assumption of risk Relative air quality

0 to 4.9 Little or no foliar injury None Good

5.0 to 14.9 Light to moderate foliar injury Low Moderate

15.0 to 24.9 Moderate to sever foliar injury Moderate Unhealthy for sensitive species

> 25 Severe foliar injury High Unhealthy

Plot-level biosite values are averaged over a 5-year sampling period and then kriging procedures are used to interpolate a surface of biological response (i.e., ozone stress) across the landscape.

The biosite index is classified into 4 response categories that are used to define and describe (1) injury severity (2) possible impact (i.e., risk) (3) ozone relative air quality

Reporting: A national map is generated and States or Regions can excerpt the image they want for reporting purposes.

Linking variables: The interpolated ozone data allows analysts to generate a predicted biosite index value for all P2 and P3 ground plots so that the ozone data can be related directly to tree growth and other FIA indicators of tree condition.

Notes on the Core Figure

Study objective: To identify forest tree species likely to exhibit regional scale ozone impacts. The spatial distribution of probable ozone injury was related to the spatial distribution of forest tree species in the study area.

Results indicated 4 tree species at risk: black cherry, loblolly pine, sweetgum and serviceberry.

Regional assessment of ozone sensitive tree species using bioindicator plants. John W. Coulston, Gretchen C. Smith, and William D. Smith.

Analytical Objective: To provide a biological interpretation of ozone relative air quality across the landscape based on the interpolated 5-year biomonitoring data.

Image Source: A national ozone biomonitoring program - results from field surveys of ozone sensitive plants in northeastern forests (1994-2000). Gretchen Smith, John Coulston, Edward Jepsen, and Teague Prichard.

A preliminary assessment of the Montreal process indicators of air pollution for the United States. (authors) John Coulston, Karl Riitters, Gretchen Smith

Monitoring for ozone injury in West Coast (OR, WA, CA) forests in 1998. Sally Campbell, Gretchen Smith, Pat Temple, John Pronos, and others

A national ozone biomonitoring program – results from field surveys of ozone sensitive plants in northeastern forests (1994-2000). Gretchen Smith, John Coulston, Ed Jepsen, and Teague Prichard

Regional assessment of ozone sensitive species using bioindicator plants. John Coulston, Gretchen Smith, William Smith

Ozone interactions with black cherry and milkweed growth, fecundity, and leaf injury in the Lake States. Ed Jepsen and James Bennett

Status Report on the Ozone Indicator: G. Smith

fiaozone.net fia.fs.fed.us (forest health data)

Examples of Completed Reports

= Basic Rationale and Analysis

= Data and Grid Information

= Regional Report Template

Basic References on Ozone and Forest Health

Chappelka, A.H. and Samuelson, L.J.: 1998, ‘Ambient ozone effects on forest trees of the eastern United States: a review’, New Phytol. 139, 91-108.

Krupa, S.V. and Manning, W.J.: 1988, ‘Atmospheric ozone: formation and effects on vegetation’, Environ. Pollut. 50, 101-137.

Miller, P.R., Stolte, K.W., Duriscoe, D.M., and Pronos, J.:1996, ‘Extant of ozone injury to trees in the western United States’, in: Evaluating Ozone Air Pollution Effects on Pines in the Western United States. USDA Forest Service General Technical Report, PSW-GTR-155, pp.1-6.

U.S. Environmental Protection Agency: 1996a, ‘Air Quality Criteria for Ozone and Related Photochemical Oxidants, Vol I of III, Section 4.0, Environmental concentrations, patterns, and exposure estimates’, EPA/600/P-93/004aF. Office of Research and Development, Washington, DC 20460.

U.S. Environmental Protection Agency: 1996b, ‘Air Quality Criteria for Ozone and Related Photochemical Oxidants, Vol II of III, Section 5.0, Environmental effects of ozone and related photochemical oxidants’, EPA/600/P-93/004aF. Office of Research and Development, Washington, DC 20460.

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