United States

Department of

Agriculture

Forest Service

Pacific Northwest

Research Station

General Technical

Report

PNW-GTR-722

June 2007

Ozone Injury in West

Coast Forests: 6 Years of

Monitoring

Sally J. Campbell, Ron Wanek, and John W. Coulston
The Forest Service of the U.S. Department of Agriculture is dedicated to the

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Authors

Sally J. Campbell is a biological scientist and Ron Wanek is a computer specialist,

Forestry Sciences Laboratory, 620 SW Main Street, Suite 400, Portland, OR 97205;

John W. Coulston is a research forester, Southern Research Station, 4700 Old

Kingston Pike, Knoxville, TN 37919.
Ozone Injury in West Coast Forests: 6 Years of

Monitoring

Sally J. Campbell, Ron Wanek, and John W. Coulston

U.S. Department of Agriculture, Forest Service

Pacific Northwest Research Station

General Technical Report PNW-GTR-722

June 2007
Abstract

Campbell, Sally J.; Wanek, Ron; Coulston, John W. 2007. Ozone injury in

west coast forests: 6 years of monitoring. Gen. Tech. Rep. PNW-GTR-722.

Portland, OR: U.S. Department of Agriculture, Forest Service, Pacific

Northwest Research Station. 53 p.

Six years of monitoring for ozone injury by the Pacific Northwest Research Station

Forest Inventory and Analysis Program are reported. The methods used to evaluate

injury, compute an injury index, and estimate risk are described. Extensive injury

was detected on ozone biomonitoring sites for all years in California, with ponderosa and Jeffrey pines, mugwort, skunkbush, and blue elderberry showing injury.

Little or no injury was detected in Oregon and Washington. The relation of observed injury to ambient ozone levels is discussed. The areas with the highest

modeled risk of ozone injury are the areas east of Los Angeles, the southern Sierra

Nevada, and portions of the central coast.

Keywords: Ozone, biomonitoring, indicator species, California, Oregon,

Washington, forest health monitoring.

Summary

Key results of ozone biomonitoring from 2000 through 2005 in California, Oregon,

and Washington by the Pacific Northwest Research Station Forest Inventory and

Analysis (FIA) Program are as follows:

• Ozone injury occurs frequently (25 to 37 percent of sampled biosites) in

California forested ecosystems demonstrating that ozone is present at

phytotoxic levels.

• The California air basins having the highest percentage of biosites with

injury were the South Coast, San Joaquin Valley, and San Diego County.

• The group of biosites in the areas with the highest ozone exposures

(SUM601 ≥25,000 parts per billion) had corresponding highest mean

percentage of injured biosites (52 percent) and highest mean biosite index

(16.4).

• In 2005, new areas (previously unreported) of ozone injury were detected

in northern California (Trinity, Plumas, and Lassen Counties) as well as in

the Mojave Desert area (San Bernadino County).

• Although ozone exposure is moderate to high over much of California,

forested areas with the highest risk were estimated (via our plant response

1

SUM60 is the sum of all hourly ozone concentrations equal to or exceeding 60 parts per

billion between 8 am and 8 pm for a certain period—in our case between June 1 and

August 31.
model) for the area east of Los Angeles, the southern Sierra Nevada, and

portions of the central coast.

• In California, an estimated 1.3 million acres of forest land and 596 million

cubic feet of wood are at moderate to high risk to impacts from ozone.

• Despite reports of increasing ozone production and exposure in Oregon and

Washington, ozone injury was observed only in the Columbia Gorge.

• Air quality as indicated by the FIA ozone bioindicator shows no consistent

pattern of increases or decreases in any of the three states between 2000

and 2005. More years of data are needed to discern any trends.

Contents

1 Introduction

1 Ozone and Forest Health in the Western United States

6 Ozone, Forest Health Monitoring, and Forest Inventory and Analysis

7 Methods

7 Biosite Locations

12 Bioindicator Species

12 Validation

14 Biosite Index

14 Exposure Analysis

15 Risk Assessment

16 Results

35 Discussion

35 California

36 Oregon and Washington

37 Research and Monitoring Needs

38 Conclusions

39 Acknowledgments

39 Metric Equivalents

39 References

47 Appendix 1: Biosite Index Calculation

49 Appendix 2: Ambient Ozone Exposure Indices Calculation and Spatial

Interpolation Methods

52 Appendix 3: Ozone Injury Risk Assessment Methods
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Ozone Injury in West Coast Forests: 6 years of Monitoring

Introduction

Tropospheric ozone and other air contaminants are stressors that affect long-term

sustainability of temperate forests throughout the world (Chappelka and Chevone

1992, Smith 1985, USDA Forest Service 1997, US EPA 1996b). Ozone has such

critical effects that it is included as one of the air quality indicators under the Forest Ecosystem Health and Vitality criterion in the Montreal Process Criteria and

Indicators for the Conservation and Management of Temperate and Boreal Forests

(Montreal Process 1995). In the United States, ozone is the only regional gaseous

air pollutant that has been measured at known phytotoxic levels at numerous remote locations across the continent (Cleveland and Graedel 1979, Lefohn and

Pinkerton 1988, Miller et al. 1997). Ozone injury to forest species in the United

States has been observed and documented since the 1950s. Although high ozone

concentrations (and injury) have been more widespread in the East (Chapellka and

Samuelson 1998, Cleveland and Graedel 1979), portions of California have had

some of the highest recorded concentrations of ozone in the United States

(Bytnerowicz et al. 2003, Carroll et al. 2003) (fig. 1).

Ozone and Forest Health in the Western United States

The adverse effects of ozone on forest health was first reported in the West in

California in the 1950s (Parmeter et al. 1962). A peculiar discoloration of the

needles of ponderosa pine (Pinus ponderosa Dougl. ex Laws.) was observed on

the west-facing slopes and ridges of the San Bernardino Mountains east of Los

Angeles (figs. 2 and 3). Needles of these pines developed yellow (chlorotic) mottling, becoming necrotic and abscising prematurely. Subsequent experimentation

confirmed that the causal agent of the foliar injury to pines and other vegetation

was exposure to high concentrations of ambient ozone originating in the urban Los

Angeles area (Miller et al. 1963). Later, in the 1970s, ozone injury was reported on

ponderosa, Jeffrey (Pinus jeffreyi Grev. & Balf.) and other pines on the western

slopes of the southern Sierra Nevada and the south coast, southeast desert, San

Joaquin, north central coast, San Francisco Bay, and San Diego air basins (Miller

and Millecan 1971, Pronos et al. 1978) (fig. 4).

The response of western trees to ozone pollution is dependent both on the tree

species and atmospheric ozone concentrations (Miller and Millecan 1971; Miller

et al. 1983, 1997). Certain forest species, such as ponderosa pine, are sensitive to

ozone at concentrations that normally occur over wide areas of the western landscape (Miller 1996, US EPA 1996b). Because of the long lifespan of trees, there is
2

General Technical Report PNW-GTR-722

Figure 1—Cumulative hourly ozone concentrations exceeding 60 parts per billion (SUM60), June 1–August 31, 8 a.m. to 8 p.m., 2001

through 2005 average. For more information on exposure estimation, see appendix 2.
3

Ozone Injury in West Coast Forests: 6 years of Monitoring

Figure 2—Ponderosa pine with ozone-induced needle loss and

discoloration.

Figure 3—Ponderosa pine with severe ozone injury

symptoms (chlortic mottle), California. Dan Duriscoe John Pronos
4

General Technical Report PNW-GTR-722

Figure 4—California air basins.
5

Ozone Injury in West Coast Forests: 6 years of Monitoring

ample opportunity for a long-term, cumulative effect on tree growth. Ozone has

been implicated in the growth decline of pollution-sensitive tree species in the Eastern United States (Benoit et al. 1982, Chappelka and Samuelson 1998, Karnosky

1981) and in pines in California (McBride et al. 1975, Miller et al. 1997, Peterson

et al. 1991). The amount of injury expressed by individuals of ozone-susceptible

species is a function of more than atmospheric ozone concentrations; it is also

related to tree age and size; site factors such as elevation, aspect, topography,

temperature, and soil moisture; and genotypic and phenotypic characteristics that

influence ozone uptake by the plant (Arbaugh et al. 1998, Miller et al. 1997,

Musselman and Massman 1999, US EPA 2006).

Ozone also has a variety of ecological effects on forested landscapes, with the

potential to alter species composition, soil moisture, and fire regimes and influence

pest interactions (McBride and Laven 1999; Miller et al. 1982; Smith 1974;

Treshow and Stewart 1973; US EPA 1996b, 2006). Ozone predisposes trees to

bark beetle (Dendroctonus spp.) attacks, especially where ozone exposure is high

(Pronos et al. 1999). In the highly impacted San Bernadino Mountain forests,

reduction of fine-root mass and carbon cycling at both the tree and ecosystem

levels has been attributed to ozone exposure (Fenn et al. 2003, Grulke et al. 1998).

Arbaugh et al. (2003) reported shifts in mixed-conifer stand composition in the San

Bernadino Mountains from predominantly ponderosa pine to predominantly white

fir (Abies concolor (Gord. & Glend.) Lindley ex Hildebr.). Similarly, simulations of

the physiological and ecological responses of ponderosa pine and white fir to

elevated ozone exposure in conifer forests in California showed a decrease in

individual tree carbon budgets as well as a subsequent decrease in abundance of

ponderosa pine (Weinstein et al. 2005).

Monitoring for ozone-induced plant injury (biomonitoring) has been carried out

for almost 30 years in California forests, primarily on pines (Dale 1996, Dursicoe

1990, Guthry et al. 1993, Miller 1996, Miller et al. 1989, Pronos and Vogler 1981,

Pronos et al. 1978) and to a limited extent on other vegetation (Duriscoe and

Temple 1996; Temple 1989, 1999). Consistent with ambient ozone levels (fig. 1),

the greatest amount of ozone injury to western forests continues to be observed in

the mountains east of Los Angeles, California, with foliar injury, premature defoliation, and growth loss commonly observed on ponderosa and Jeffrey pines. Injury

also has been reported in this area on other tree species such as bigcone Douglas-fir

(Pseudotsuga macrocarpa (Vasey) Mayr) (Peterson et al. 1995) and California
6

General Technical Report PNW-GTR-722

black oak (Quercus kelloggii Newb.) (Miller 1996) and on understory plants such as

blue elderberry (Sambucus mexicana Presl.), artemisia species (Artemisia spp.),

evening primrose (Oenothera elata Kunth.), and others (Temple 1999). In the Sierra

Nevada, ozone injury has been reported on ponderosa and Jeffrey pines since the

1970s and continues to be common on these species (Arbaugh et al. 1998, Carroll et

al. 2003, Duriscoe 1990, Miller 1996, Pronos et al. 1978).

Elevated ozone concentrations also occur downwind of Pacific Northwest

urban areas such as Vancouver, British Columbia; Seattle, Tacoma, and Vancouver,

Washington; and Portland, Oregon (Bohm 1989, Brace and Peterson 1998, Cooper

and Peterson 2000, Edmonds and Basabe 1989, Fenn et al. 2005). Visible injury or

other effects on tree health have not been observed, however, in forests in these

areas (Campbell et al. 2000, Duriscoe and Temple 1996, USDI NPS 2006).

Ozone, Forest Health Monitoring, and Forest Inventory and

Analysis

In the 1990s, the Forest Health Monitoring (FHM) Program, begun as a partnership

between the U.S. Environmental Protection Agency and the USDA Forest Service,

began measuring a number of forest health indicators in order to assess changes in

the health of U.S. forests. One of the FHM indicators was ozone injury to indicator

species. In 2000, measurement of forest health indicators, including ozone injury,

was transitioned from the FHM Program to the Forest Inventory and Analysis1

(FIA) Program. The FHM/FIA biomonitoring approach observes and documents

injury to susceptible conifers, hardwoods, and understory perennials annually on a

network of sites (biosites) distributed across the Nation—it is likely the most

comprehensive ozone biomonitoring program worldwide.

Results from the first year of FHM/FIA ozone biomonitoring in west coast

states, 1998, were reported in 2000 (Campbell et al. 2000). Plant injury was detected at only one biosite in Washington and at no biosites in Oregon or California.

Injury was present, however, on other ozone injury monitoring plots in the Sierra

and Sequoia National Forests in California in 1997 and 1998 (measured by the Forest Service Region 5 Forest Health Protection program and reported by Campbell

1

 The FIA Program is a national USDA Forest Service research program with four regions:

North, South, Intermountain, and West Coast.
7

Ozone Injury in West Coast Forests: 6 years of Monitoring

et al. 2000). Since 1998, many more FIA ozone biosites have been established in

these three states (fig. 5), and injury has been observed frequently and consistently

at many sites in California and at one site in Washington.

This publication addresses key assessment questions posed by Smith et al. (in

press) for the FIA ozone indicator, including:

• Are phototoxic concentrations of ozone present in the forest ecosystems of

California, Oregon, and Washington?

• Is the air quality (e.g., ozone pollution) of the west coast states changing

over time?

• If so, is it improving or deteriorating?

Additional questions are also addressed:

• Where is ozone injury the highest and most frequent?

• What is the relation, over a broad landscape, between ozone injury and

ozone exposure?

• What amount of forest land and timber volume is at risk and where is it?

Methods

Biosite Locations

Each year, 70 to 132 ozone biosites per year were visited in Washington, Oregon,

and California between 2000 and 2005 (table 1, figs. 5 through 9). Beginning in

2001, an ozone biosite grid was developed (fig. 10), separate from the regular FIA

plot grid; biosites were more closely spaced in areas of higher potential ozone

exposure and higher density of sensitive species (Smith et al. 2001). The alternate

grid, not tied to the regular FIA forested plots, also provided the flexibility to search

for and establish ozone plots per the biosite criteria defined by the FIA Program

(USDA Forest Service 2000-2005) for access, location, size of canopy opening,

bioindicator species and plant counts, soil condition, and disturbance (table 2). In

west coast states, biosites are located exclusively on public lands because there is

adequate distribution of public forests and, with the exception of the National Park

Service, it saves the need each year to acquire landowner permission to visit each

site. By 2003, almost all polygons of the new grid were populated with at least one

biosite. The primary reason for not populating a polygon was not finding a biosite

on public land that met the criteria in table 2.

Text continues on page 12
8

General Technical Report PNW-GTR-722

Figure 5—West Coast Forest Inventory and Analysis ozone biomonitoring sites, 2000-2005.
9

Ozone Injury in West Coast Forests: 6 years of Monitoring

Table 1—Number of Forest Inventory Analysis ozone biosites by

state and year

2000 2001 2002 2003 2004 2005

California 22 29 61 65 65 65

Oregon 20 22 34 35 35 35

Washington 28 27 30 32 27 32

Figure 6—Central Sierra Nevada ozone biosite with trembling aspen and

ponderosa pine as two of the indicator species, California.

Figure 7—High-elevation ozone biosite with thin-leaf huckleberry as one of

the indicator species, Oregon.

Dan Duriscoe Alan Kanaskie
10

General Technical Report PNW-GTR-722

Figure 8—Southern Sierra Nevada ozone biosite with blue elderberry as one of

the indicator species (plant in foreground).

Dan Duriscoe

Figure 9—Ozone biosite in public park with Jeffrey pine as the indicator species,

Washington.

Sally Campbell
11

Ozone Injury in West Coast Forests: 6 years of MonitoringFigure 10—Forest Inventory and Analysis ozone biomonitoring grid.
12

General Technical Report PNW-GTR-722

Table 2—Criteriaa used by the Forest Inventory and Analysis Program to select ozone

biomonitoring sites

First choice = best site Second choice

Access Easy Easy

Location Single location 1 or 2 locations (split-plot)

Size of opening >1.2 ha (3 ac); wide open 0.405 to 0.2 ha (1 to 3 ac);

area; <50% crown closure long, narrow, or irregularlysized opening

Species count >3 species >2 species

Plant count 30 plants of 3 species; 30 plants of 2 species;

10 to 30 plants of additional 10 to 30 plants of additional

species species

Soil conditions Low drought potential; Moderately dry; moderate

good fertility fertility

Site disturbance No recent (1 to 3 years) distur- Little or no disturbance; no

bance; no obvious soil obvious soil compaction

compaction

a

Criteria have changed slightly between 2000 and 2005; see FIA ozone field protocol, 2000 through

2005 (USDA Forest Service 2000, 2001, 2002, 2003, 2004, 2005)

Bioindicator Species

Based on controlled exposure studies and field observations (Brace et al. 1996,

Duriscoe and Temple 1996, Mavity et al. 1995), a list of bioindicator species was

developed for the west coast states (table 3). Ozone injury data were collected at

biosites each year within a 4- to 6-week period (July 15–August 30) by contract,

state, or Forest Service crews. Ten to thirty plants of up to three bioindicator species at each site were rated for amount of ozone injury and severity of symptoms

(fig. 11, table 4). All ozone crews were trained to select ozone biosites, identify

indicator species, and measure ozone injury. Each crew was audited at least once

(usually twice) per field season during 2003-2005, with a blind remeasurement by a

quality assurance crew.

Validation

The FIA ozone biomonitoring protocol requires that crews (both production and

quality assurance) collect vouchers of every bioindicator species exhibiting suspected ozone injury at a biosite and send specimens to an ozone expert for validation of the injury. The voucher consists of three leaves that clearly show ozone

injury (for broadleaved plant species) or two small branches containing a full

complement of needles showing chlorotic mottle (for pine species). For the west
13

Ozone Injury in West Coast Forests: 6 years of Monitoring

Table 3—Ozone-sensitive plant species used as bioindicators for Forest Inventory and Analysis ozone biomonitoring in California, Oregon, and Washington

Common name Scientific name

Blue elderberry Sambucus mexicana Presl

California black oaka Quercus kelloggii Newberry

Evening primrose Oenothera elata Kunth.

Jeffrey pine Pinus jeffreyi Grev. & Balf.

Mugwort Artemisia douglasiana Bess. ex Hook.

Ninebark Physocarpus malvaceus (Greene) Kuntze

Pacific ninebarkb Physocarpus capitatus (Pursh) Kuntze

Ponderosa pine Pinus ponderosa P. & C. Lawson var. ponderosa

Quaking aspen Populus tremuloides Michx.

Red alder Alnus rubra Bong.

Red elderberry Sambucus racemosa L.

Scouler’s willow Salix scouleriana Barratt ex. Hook.

Skunkbush Rhus trilobata Nutt.

Snowberry Symphoricarpos spp.

Western wormwood Artemisia ludoviciana Nutt.

Thinleaf huckleberry Vaccinium membranaceum Dougl.

a

 Dropped as bioindicator plant in 2002.

b

 This species found west of Cascades only.

Figure 11—Examination of thin-leaf huckleberry for ozone injury, Oregon.

Tom Iraci
14

General Technical Report PNW-GTR-722

coast states of California, Oregon, and Washington, the same expert provided

validation services for vouchers from all years reported here (2000 to 2005). All

positive injury results presented in this report are for validated injury as reported by

production crews.

Biosite Index

A biosite index (BI) is calculated from the amount and severity of injury (table 4)

recorded for each evaluated plant. The BI is a value that reflects local air quality

and bioindicator response and therefore the potential risk of ozone impact in the

area represented by that biosite. A BI value—the midrange values for amount times

the midrange values for severity averaged for each species and then averaged across

all species on the biosite—is calculated for each biosite. The BIs were then classified into four risk categories (table 5) used in the risk assessment described below.

See appendix 1 for the BI formula and an example of a calculated BI for one

biosite.

Exposure Analysis

The relationships between average ambient ozone and various measures of injury

(BI and percentage of plots with injury) were examined. We used the 2001-2005

average ozone exposure, SUM60 (US EPA 2006), interpolated across the landscape

to provide a continuous surface, which was then grouped into several different

classes of exposure (fig. 1). The metric, SUM60, a common metric for ozone

exposure, is the sum of all hourly ozone concentrations equal to or exceeding 60

parts per billion (ppb) between 8 a.m. and 8 p.m. for a certain period—in our case

Table 4—Ozone injury rating system for amount and for

severity

Injury Midrange values used

rating Range in calculations

Percent

0 00

1 1-6 .03

2 7-25 .16

3 26-50 .38

4 51-75 .63

5 >75 .875

Note: A rating applies to each of amount (percentage of the plant’s leaves

or needles that have ozone symptoms) and severity (average percentage of

leaf or needle area with symptoms for injured foliage). Scale from USDA

FS 2005.
15

Ozone Injury in West Coast Forests: 6 years of Monitoring

between June 1 and August 31. Overlaying the exposure map with biosite locations

allowed us to look at the level of exposure to which each biosite was subjected.

The FIA ozone biomonitoring program has developed an application that

calculates ozone exposures by using data from the U.S. Environmental Protection

Agency (EPA) Aerometric Information Retrieval System database by month and

over a standard growing season (May 1-Sept. 31) and a user-defined growing

season for a daylight (12-hour) and 24-hour period for a wide variety of common

indices. See appendix 2 for the exposure analysis methods.

Risk Assessment

One goal of the FIA ozone biomonitoring program is to appraise the likelihood

of an undesirable response of forests to ambient ozone conditions. We use a risk

assessment approach that was suggested by Smith et al. (in press), demonstrated by

Coulston et al. (2003), and consistent with the ecological risk assessment paradigm

described by Regens (1995). Table 5 provides a quantitative description of observed

plant response to ambient ozone conditions (biosite index), and a qualitative description of risk and possible impacts. However, plant injury to bioindicator species

from ozone is recorded on biosites, which are generally open areas that may or may

not meet the FIA requirements of forest land and use bioindicator species that may

or may not be forest tree species. Therefore, to evaluate the likelihood of ozone

injury to forest trees, we use spatial interpolation to extend the information collected at biosites to the forest population (Coulston et al. 2003; Smith et al., in

press).

We interpolated gridded maps of the BI for each year, 2000-2005, via gradient

inverse distance weighting (GIDS). The GIDS was first proposed as a way to

Table 5—Biosite index categories (risk categories) and risk assumptionsa

Biosite index Biosite index category Risk assumption

0 to 4.9 1 = little or no foliar injury None. Tree-level response. Visible injury to

leaves and needles.

5 to 14.9 2 = low foliar injury Low. Tree-level response. Visible and

invisible injury.

15 to 24.9 3 = moderate foliar injury Moderate. Tree-level response. Visible

and invisible injury.

≥25 4 = severe foliar injury High. Structural and functional changes.

Visible and invisible injury.

a Coulston et al. 2003.
16

General Technical Report PNW-GTR-722

interpolate climatic data on a broad spatial scale as input for plant growth models

(Nalder and Wein 1998). The GIDS technique combines multiple linear regressions

with inverse distance weighting interpolation and, like other recently developed

interpolation techniques, incorporates elevation as a covariate. See appendix 3 for

further details.

The six interpolated BI maps were averaged to create the final risk map (average 2000-2005 BI) (fig. 12). We then overlaid the final risk map with FIA plots.

This variable (2000-2005 BI) could then be used to summarize the FIA survey data.

At this point, we used the methods suggested by Bechtold and Patterson (2005) to

estimate the acres of forest land and the volume of susceptible tree species in each

BI risk category.

Results

With the exception of one site in Washington, ozone injury occurred only in California. The percentage of biosites with injury was relatively stable between 2000

and 2005, varying between about 25 percent in 2003 and almost 37 percent in 2001

and 2005 in California and between 0 and 4 percent in Washington (table 6). The

number of plants evaluated increased each year as more biosites were added and as

crews located additional species on the biosite or replaced existing biosites that had

low species or plant counts with ones that had more species or plants (table 7). The

Washington biosite with positive injury is located within the Columbia Gorge, east

and downwind of Portland, Oregon, and Vancouver, Washington. The injured species is offsite (planted) Jeffrey pine in an irrigated setting. In California, five species

exhibited validated ozone injury: blue elderberry, Jeffrey pine, mugwort (Artemisia

douglasiana Bess. ex Hook.), ponderosa pine, and skunkbush (Rhus trilobata Nutt.)

(figs. 13a through 17). The species that showed the greatest proportion of injured to

sampled plants, across all years, was ponderosa pine (table 8, fig. 18).

Although the number of sites or species with injury is informative, the average

biosite injury index (which takes into account both severity and amount of injury on

multiple species at a site) provides a more meaningful measure of injury on biosites

across the state that can be compared from year to year. In California, the average

biosite injury index was highest in 2000 and 2005, indicating that injury, where it

occurred, was more severe (higher level of injury on individual plants) than in other

years (table 9). However, more meaningful trend analyses will be those that focus

on comparisons between mean values for different sets of years such as comparing

Text continues on page 23
17

Ozone Injury in West Coast Forests: 6 years of Monitoring

Figure 12—Biosite index estimates and risk to forests of injury from ozone exposure, 2000–2005 average. For more information on

ozone risk assessment, see appendix 3.
18

General Technical Report PNW-GTR-722

Table 6—Number and percentage of Forest Inventory and Analysis biosites

with validated ozone injury, by year

2000 2001 2002 2003 2004 2005

California

Number 6 11 20 16 22 24

Percent 27.3 36.7 30.8 24.6 33.8 36.9

Oregon

Number 0 0000 0

Percent 0 0000 0

Washington

Number 1 1011 1

Percent 3.8 3.7 0 3.1 3.7 3.1

Table 7—Number of plants evaluated and injuredaon Forest Inventory and

Analysis biosites, by year

2000 2001 2002 2003 2004 2005

California

Evaluated 1,078 1,492 3,865 4,295 4,370 4,177

Injured 98 114 207 119 165 254

Oregon

Evaluated 964 963 2,764 2,909 2,901 2,845

Injured 0 0000 0

Washington

Evaluated 1,281 1,250 2,072 2,693 2,497 2,490

Injured 7 6044 5

a Injury validated by expert.
19

Ozone Injury in West Coast Forests: 6 years of Monitoring

Figure 13a—Blue elderberry with light ozone injury symptoms (interveinal necrosis), California.

Dan Duriscoe

Figure 13b—Blue elderberry with moderate ozone injury

symptoms (interveinal necrosis), California.

Dan Duriscoe Dan Duriscoe

Figure 13c—Blue elderberry with severe ozone injury

symptoms (interveinal necrosis), California.
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General Technical Report PNW-GTR-722

Figure 14—Jeffrey pine needles with light ozone injury

symptoms (chlorotic mottle), California.

Dan Duriscoe

Figure 15—Mugwort with artificially induced ozone injury

symptoms (chlorosis and premature senescence).

Pat Temple
21

Ozone Injury in West Coast Forests: 6 years of Monitoring

Figure 16a—Ponderosa pine with moderate severity of ozone

injury symptoms (chlorotic mottle), California.

Dan Duriscoe

Figure 16b—Ponderosa pine with severe ozone injury (chlorotic

mottle), California.

Dan Duriscoe

Figure 17—Skunkbush with artificially induced ozone injury

symptoms (necrotic stippling).

Pat Temple
22

General Technical Report PNW-GTR-722

Table 8—Plants evaluated and injuredaon Forest Inventory and Analysis biosites,

by species, by year, California

2000 2001 2002 2003 2004 2005

Blue elderberry

Evaluated 100 133 452 499 407 304

Injured 31 31 41 7 17 7

California black oakb

Evaluated 43 13 — — — —

Injured 0 0 — — — —

Jeffrey pine

Evaluated 161 330 410 480 566 563

Injured 2 28 60 15 57 58

Mugwort

Evaluated 120 187 599 600 632 684

Injured 13 3 0 5 0 0

Pacific ninebark

Evaluated 0 0 30 30 22 30

Injured 0 0 0 0 0 0

Ponderosa pine

Evaluated 325 434 984 1,016 1,112 1,075

Injured 52 52 106 92 97 181

Quaking aspen

Evaluated 159 166 237 288 322 313

Injured 0 0 0 0 0 0

Red alder

Evaluated 0 0 112 120 120 90

Injured 0 0 0 0 0 0

Red elderberry

Evaluated 0 0 30 30 47 30

Injured 0 0 0 0 0 0

Scouler’s willow

Evaluated 0 25 100 96 60 90

Injured 0 0 0 0 0 0

Skunk bush

Evaluated 0 0 254 270 328 262

Injured 0 0 0 0 0 8

Snowberry

Evaluated 170 204 627 776 724 706

Injured 0 0 0 0 0 0

Western wormwood

Evaluated 0 0 30 90 30 30

Injured 0 0 0 0 0 0

a Injury validated by expert.

b

 No data 2002 through 2005 because dropped as bioindicator plant in 2002.
23

Ozone Injury in West Coast Forests: 6 years of Monitoring

the mean for 2000-2004 to that for 2005-2009 or a comparison of 2000-2004 to

2001-2005 to 2002-2006 and so on. We will make these types of trend analyses as

we collect additional years of data.

In California, the distribution of biosites with injury was fairly constant from

year to year, with injury detected in the following key areas: south central and south

coast (north and east of Los Angeles), San Diego County, the Sierra Nevada (with

more injury in the southern portion), and San Francisco Bay (figs. 19 through 24).

In 2005, injury was detected for the first time farther north in the north coast area

Figure 17—Percentage of evaluated plants with ozone injury, California, 2000-2005.

Table 9—Number and percentage of biosites by biosite index categorya in California,

by year

Biosite index 2000 2001 2002 2003 2004 2005

0 to 4.9 (least injured)

Number 18 24 52 56 57 48

Percent 81.8 82.8 85.2 86.2 87.7 73.8

5.0 to 14.9

Number 1 2 7 7 3 2

Percent 4.5 6.9 11.5 10.8 4.6 3.1

15.0 to 24.9

Number 0 1 1 1 3 5

Percent 0.0 3.4 1.6 1.5 4.6 7.7

≥25.0 (most injured)

Number 3 2 1 1 2 10

Percent 13.6 6.9 1.6 1.5 3.1 15.4

Average biosite index 6.7 3.4 2.2 2.1 2.5 9.3

a See appendix 1 for calculation of biosite index.

Text continues on page 30
24

General Technical Report PNW-GTR-722

Figure 19—Forest Inventory and Analysis ozone biosites and biosite index, California, 2000.
25

Ozone Injury in West Coast Forests: 6 years of Monitoring

Figure 20—Forest Inventory and Analysis ozone biosites and biosite index, California, 2001.
26

General Technical Report PNW-GTR-722

Figure 21—Forest Inventory and Analysis ozone biosites and biosite index, California, 2002.
27

Ozone Injury in West Coast Forests: 6 years of Monitoring

Figure 22—Forest Inventory and Analysis ozone biosites and biosite index, California, 2003.
28

General Technical Report PNW-GTR-722

Figure 23—Forest Inventory and Analysis ozone biosites and biosite index, California, 2004.
29

Ozone Injury in West Coast Forests: 6 years of Monitoring

Figure 24—Forest Inventory and Analysis ozone biosites and biosite index, California, 2005.
30

General Technical Report PNW-GTR-722

(Trinity County) and in the northeastern portion of the Sierra Nevada (Plumas and

Lassen Counties) as well as in the Mojave Desert area (San Bernadino County).

Summaries of injury are depicted as average BI, by biosite (fig. 25) and as percentage of biosites with validated injury, by air basin (figs. 26 and 4).

California FIA biosite data were also summarized by ozone exposure levels

depicted in figure 1. Areas where the average ozone exposure exceeded a SUM60

of 25,000 ppb had a higher percentage of biosites with injury (fig. 27) and higher

average BI (fig. 28). Averages across all years for both percentage injured and BI

are more comparable to exposure class than year-to-year values, as the SUM60

exposure map is an average across several years as well. A scatter graph of each

biosite’s average BI and the average exposure there further illustrates that, when

looking at individual biosites, relatively high levels of injury can occur in areas

where the 5-year average of ozone exposure is low or alternatively, low levels of

injury can occur in areas of high exposure (fig. 29).

Using the gradient plus inverse distance weighting risk model described in

“Methods” (p. 6) to predict risk, the areas at greatest risk from ozone injury in

California are the southern Sierra Nevada, portions of the central coast, and much

of the area east of Los Angeles (fig. 12). The majority of ozone-susceptible trees in

California are not at risk; about 25 million acres (76 percent) of forest land area

with 87 percent of the tree volume of susceptible species is classified in the lowest

BI risk category (BI<5, no risk, tables 5, 10, and 11). However, more than 8 million

acres with 5.5 billion cubic feet (13 percent) of susceptible tree species are at low,

moderate, or high risk (BI ≥5). About 18 percent of ponderosa pine volume and

29 percent of Jeffrey pine volume, two species that consistently show injury in the

field, are estimated to be at low or moderate risk (table 11). About 1.2 percent of

the volume of Douglas-fir (Pseudotsuga menzesii (Mirb.) Franco), although not a

species on which ozone injury has been observed in the field, is estimated to be

at moderate or high risk (table 11). In Oregon and Washington, all forest land area

and all susceptible species in Oregon and Washington are classified in the lowest

BI/risk category (BI <5, no risk) (table 10). The area showing higher risk in the

Columbia Gorge is not forested so there are no forested acres or volume of susceptible species at risk.

Text continues on page 35
31

Ozone Injury in West Coast Forests: 6 years of Monitoring

Figure 25—Forest Inventory and Analysis ozone biosites and average biosite index, California, 2000-2005.
32

General Technical Report PNW-GTR-722

Figure 26—Percentage of biosite visits recording injury, by California air basin, 2000-2005. Numbers in parentheses

after air basin label are the number of biosites in the basin followed by the total number of visits to those biosites

between 2000 and 2005.
33

Ozone Injury in West Coast Forests: 6 years of Monitoring

Figure 27—Percentage of biosites with injury, by ozone exposure class, by year, California.

Figure 28—Average biosite index, by exposure class, 2000-2005, California. For more information on biosite index,

see appendix 1.
34

General Technical Report PNW-GTR-722

Figure 29—Relationship between average biosite index, 2000-2005, and average ozone exposure,

2001-2005, California. For more information on biosite index, see appendix 1.

Table 10—Estimated area of forest land and volume of ozone-susceptible tree

species, by biosite index and risk category, by state

State and Volume of

biosite index a Area of forest land susceptible species b

Million acres Million cubic feet

California:

0 to 4.9, no risk 25.15 36,429.25

5 to 14.9, low risk 7.36 4,059.28

15 to 24.9, mod risk .67 560.18

≥25, high risk .63 36.11

Oregon:

0 to 4.9, no risk 30.47 74,478.25

5 to 14.9, low risk 0 0

15 to 24.9, mod risk 0 0

≥25, high risk 0 0

Washington:

0 to 4.9, no risk 22.12 65,035.59

5 to 14.9, low risk 0 0

15 to 24.9, mod risk 0 0

≥25, high risk 0 0

a Biosite index based on interpolated values for each Forest Inventory and Analysis plot; see

appendix 3 for interpolation methods.

b Species susceptibility based on both field observations and fumigation trials.
35

Ozone Injury in West Coast Forests: 6 years of Monitoring

Discussion

California

Although ozone and its precursors have been decreasing throughout the state since

1975, several air basins in California still experience high levels of ozone (Cox et

al. 2006). These include the South Coast Air Basin (the area around and east of Los

Angeles with 43 percent of California’s population) and the San Joaquin Valley Air

Basin (the southern portion of the California Central Valley with 10 percent of

California’s population) (fig. 26). These two areas also contribute ozone and ozone

precursors to a number of other downwind air basins including Great Basin Valleys,

Mojave Desert, Mountain Counties, North and South Central Coast, Sacramento,

and San Diego. Examination of up to the highest 10 FIA ozone BIs each year

between 2000 and 2005 (n = 56, as year 2000 had only 6 biosites with any injury)

shows that 88 percent of these occur in the South Coast and San Joaquin Valley or

the downwind air basins mentioned above.

Air quality is a significant concern in national parks, with mandates to protect

air quality via the 1916 Organic Act and the 1963 Clean Air Act (and its 1970 and

1990 amendments) with many elements (such as vegetation, visibility, water

quality, and panoramas) of a park environment identified as being sensitive to air

Table 11—Estimated volume of ozone-susceptible tree species by species and biosite

index (BI)a and risk category, California

BI

0 to 4.9 5 to 14.9 15 to 24.9 ≥25

Species (no risk) (low risk) (mod risk) (high risk)

Million cubic feet

Red alder 430.51 4.61 0 0

Lodgepole pine 2,253.57 1,174.53 97.95 0

Jeffrey pineb 3,191.34 1,260.43 67.40 0

Ponderosa pineb 6,941.44 1,387.60 106.90 0

Monterey pine 0 0 14.59 0

Quaking aspenb 58.07 2.38 0 0

Black cottonwood 66.26 5.89 0 0

Douglas-fir 20,747.91 475.06 225.36 36.11

California black oakb 2,568.60 648.77 47.99 0

Western hemlock 171.55 0 0 0

All susceptible species 36,429.25 4,959.28 560.18 36.11

a Biosite index based on interpolated values for each Forest Inventoy and Analysis plot; see appendix 3

for interpolation methods.

b Ozone injury observed in the field on these species; other species demonstrated susceptibility

following fumigation with ozone.
36

General Technical Report PNW-GTR-722

pollution (NAS 2004). The NPS has committed to managing their air resources

through activities such as inventories of air-quality-related values, monitoring air

quality in the parks, and evaluating air pollution effects and causes. In California,

ambient ozone levels increased significantly in the Sequoia and Death Valley

National Parks between 1995 and 2004, exceeding the EPA’s national ambient

air quality standard2

 (USDI NPS 2006). However, FIA biosites in these two parks

(one each) showed consistent low injury (average BI = 13.2 for the Sequoia National Park and no detected injury for Death Valley National Park). For the five FIA

ozone biosites located in national parks in California, including the above two,

injury was detected 39 percent of the time between 2000 and 2005, with an average

BI of 5.7, and maximum BI of 43.

The model we used to predict risk of ozone injury across the west coast is a

plant response model, where the plants themselves integrate climatic (e.g., temperature and precipitation), site (e.g., moisture, elevation), and genetic factors to

influence ozone uptake and their response to it. Other models such as those reported

by Bytnerowicz et al. (2003: chapters 7 through 9) are exposure models that use

ambient ozone data and climatic, topographic, and site factors to predict areas of

high ozone exposure. These, like the SUM60 maps, will coincide generally but

often not specifically, with our reported areas of injury and high BIs. Bytnerowiscz

et al. (2003) found that patterns of ozone injury in the western Sierra Nevada

generally followed patterns of ozone exposure risk predicted by several exposure

models.

Oregon and Washington

Although California has monitored ozone for many years, Oregon and Washington

have little or no pre-1980s data on ozone air quality (Bohm 1989, US EPA 1996a).

Until recently, the forests in Oregon and Washington were assumed to be relatively

clean with only occasional intrusions of above-background concentrations of

ambient ozone (Brace and Peterson 1998, Cooper and Peterson 2000). However,

increases in ambient ozone have been observed in a number of western Washington

locations between 1999 and 2003, including Mount Rainier and North Cascades

National Parks (Fenn et al. 2005, USDI NPS 2006).

2

The national ozone standard: ozone levels not to exceed 0.08 parts per million for 8 hours,

based on the 4th highest concentration averaged over 3 years. (www.epa.gov/ttn/naaqs/ozone/

03imp8hr/finalrule.html.) “An area violates the federal 8-hour ozone standard if the calculated fourth highest 8-hour concentration averaged over a three-year period exceeds the

level of the standard at any monitoring site in the region” (Cox et al. 2006).
37

Ozone Injury in West Coast Forests: 6 years of Monitoring

The Columbia River Gorge, where ozone levels in the Gorge rise as distance

from the Portland, Oregon/Vancouver, Washington, metropolitan area increases,

levels as high as 0.079 parts per million (ppm) for 8 hours in 2001 were reported at

Wishram, Washington (96 miles east of Portland). The injury detected in the Gorge

by the FIA ozone biomonitoring program was at a biosite a little over 100 miles

east of Portland in an irrigated area that is naturally nonforested. Although the

presence of injury is atypical there, this site supports ambient data showing that

ozone levels are high there and capable of causing injury to susceptible species,

forest or nonforest, given favorable environmental conditions.

The FIA ozone data provide a baseline of no injury and no risk in Oregon and

Washington forests against which future data can be compared. Climate change and

population growth in these two states suggest that ground-level ozone generation

and injury is more likely, rather than less, to increase in coming years. For all three

states, analyses of trends will be more meaningful as more data are collected and, as

mentioned on pages 15 and 22, comparisons can then be made between mean

values for different sets of years.

Research and Monitoring Needs

Ozone research and monitoring needs for the Sierra Nevada in California are well

described in Bytnerowicz et al. (2003) and are applicable to other parts of California as well as Oregon and Washington—refinement of ambient monitoring technologies, development of more sophisticated pollution distribution and biological

response models, integrated monitoring networks, alternative ways to assess ozone

uptake and injury, identification of additional bioindicator species, better linkage

between air levels and visible injury, and integrated assessments of urban and wildland pollution. Additional research is needed to elucidate the role of other stressors

such as insects, diseases, nitrogen deposition, and climate change in relation to

ozone uptake and effects.3

 We also need to better understand the role and contribution of ozone and its precursors from out-of-country emittors such as Asia or

Mexico (Fenn et al. 2005).

3

Arbaugh, M. 2006. Personal communication. Statistician. Air pollution and global change

impacts on western forest ecosystems research unit, Pacific Southwest Research Station,

Forest Fire Lab, 4955 Canyon Crest Drive, Riverside, CA 92507.
38

General Technical Report PNW-GTR-722

Conclusions

Although several important pieces of California legislation have been implemented

for pollution abatement since the 1980s and per-car emissions have been reduced in

the state from the very high levels of the 1970s and 1980s, ozone standards4 are still

being exceeded in several California air basins (Cox et al. 2006). With changes in

global and regional climate, increases in populations and anthropogenic sources of

pollution, and greater potential for disturbance events such as wildfires and insect

and disease outbreaks, forests are increasingly vulnerable.

The FIA network of biosites is designed to detect the first visible sign of ozone

stress and establish regional and national trends from a real baseline condition

(Smith et al., n.d.). It has tremendous value as one of few large-scale biological

networks of ozone air quality. This information can inform governments, the public,

and industry in determining air pollution guidelines, regulations, and laws. The FIA

ozone injury data serve as a source of information about the effects of ozone on

forest plants that is complementary and enhances that provided by ambient ozone

monitoring systems. The FIA ozone data can also serve as a resource to aid land

managers in local forest management (species selection in high-exposure areas, tree

improvement programs, etc.) and planning for future forest health and condition.

The FIA ozone biomonitoring from 2000 through 2005 in California, Oregon,

and Washington tells us the following:

• Ozone injury occurs frequently (25 to 37 percent of sampled biosites) in

California forested ecosystems demonstrating that ozone is present at

phytotoxic levels.

• The California air basins with the highest percentge of biosites with injury

were the South Coast, San Joaquin Valley, and San Diego County.

• The group of biosites in the areas with the highest ozone exposures

(SUM60 ≥25,000 parts per billion) had corresponding highest mean

percentage of injured biosites (52 percent) and highest mean biosite index

(16.4).

• In 2005, new areas (previously unreported) of ozone injury were detected in

northern California (Trinity, Plumas, and Lassen Counties) as well as in the

Mojave Desert area (San Bernadino County).

4

The California ozone standard: ozone levels not to exceed 0.07 ppm averaged over 8 hours.

This standard was implemented in January 2006; the previous standard was ozone levels not

to exceed 0.09 ppm for 1 hour (Cox et al. 2006).
39

Ozone Injury in West Coast Forests: 6 years of Monitoring

• Although ozone exposure is moderate to high over much of California,

forested areas with the highest risk were estimated (via our plant response

model) for the area east of Los Angeles, the southern Sierra Nevada, and

portions of the central coast.

• In California, an estimated 1.3 million acres of forest land and 596 million

cubic feet of wood are at moderate to high risk to impacts from ozone.

• Despite reports of increasing ozone production and exposure in Oregon and

Washington, ozone injury was observed only in the Columbia Gorge.

• Air quality as indicated by the FIA ozone bioindicator shows no consistent

pattern of increases or decreases in any of the three states between 2000

and 2005. More years of data are needed to discern any trends.

Acknowledgments

We thank Elaina Graham for producing the maps for this report; Pat Temple for

contribution of introduction information, crew training, quality assurance, sample

validation, and manuscript review; Teague Prichard for the ambient ozone exposure

analysis and map; Dan Duriscoe and John Pronos for assistance with crew training

and quality assurance; Duck Creek employees, John Dale, Diane Hildebrand, Karen

Ripley, Dan Omdal, Alan Kanaskie, and Oregon Department of Forestry crew for

data collection efforts; and Sarah Jovan, Olaf Kuegler, Gretchen Smith, Mike

Arbaugh, Rick Graw, and Trent Procter for reviewing the manuscript.

Metric Equivalents

1 acre = 0.405 hectare

1 foot = 0.305 meter

1 cubic foot = 0.0283 cubic meter

1 mile = 1.609 kilometers

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Regens, J.L. 1995. Ecological risk assessment: issues underlying the paradigm. In:

Mazaika, R.; Lackey, R.T.; Friant, S.L., eds. Ecological risk assessment: use,

abuse, and alternatives. Amherst, MA: Amherst Scientific Publishers: 344–347.
45

Ozone Injury in West Coast Forests: 6 years of Monitoring

Smith, G.C.; Coulston, J.W.; O’Connell, B. [In press]. Ozone bioindication and

forest health: a guide to the evaluation, analysis, and interpretation of ozone

indicator data in the Forest Inventory and Analysis Program. Gen. Tech. Rep.

Research Triangle Park, NC: U.S. Department of Agriculture, Forest Service,

Southern Research Station.

Smith, G.C.; Coulston, J.W.; Smith W.D. [N.d.]. Ozone biomonitoring sampling

and estimation. Manuscript in preparation. On file with: G. Smith, Department

of Forestry and Wildlife, University of Massachusetts, Holdsworth Natural

Resource Center, Amherst, MA 01003.

Smith, W.D.; Coulston, J.W.; Smith, G.C. 2001. Development of the ozone

indicator sampling grid. 29 p. Unpublished manuscript. On file with: U.S.

Department of Agriculture, Forest Service, Southern Research Station, Forest

Health Monitoring Program, Forestry Sciences Laboratory, 3041 Cornwallis

Road, Research Triangle Park, NC 27709.

Smith, W.H. 1974. Air pollution—effects on the structure and function of the

temperate forest ecosystem. Environmental Pollution. 6: 11–129.

Smith, W.H. 1985. Forest quality and air quality. Journal of Forestry. 83(2):

82–92.

Temple, P.J. 1989. Oxidant air pollution effects on plants of Joshua Tree National

Monument. Environmental Pollution. 57: 35–47.

Temple, P.J. 1999. Effect of ozone on understory vegetation in the mixed conifer

forest. In: Miller, P.R.; McBride, J.R., eds. Oxidant air pollution impacts in the

montane forests of southern California. Ecological Studies 139. New York, NY:

Springer-Verlag: 208–222.

Treshow, M.; Stewart, D. 1973. Ozone sensitivity of plants in natural

communities. Biological Conservation. 5: 209–214.

U.S. Department of Agriculture, Forest Service. 1997. USDA Forest Service first

approximation report for sustainable forest management of the United States on

the criteria and indicators for sustainable management of temporal and boreal

forests, June 1997. Washington, DC. 215 p.
46

General Technical Report PNW-GTR-722

U.S. Department of Agriculture, Forest Service. 2000, 2001, 2002, 2003, 2004,

2005. Field instructions for the annual inventory of Washington, Oregon, and

California (year). Supplement for Phase 3 (FHM) ozone bioindicator plants

(west). Portland, OR: Pacific Northwest Research Station, Forest Inventory and

Analysis Program. Annual.

U.S. Department of the Interior, National Park Service [USDI NPS]. 2006. 2005

annual performance and progress report: air quality in national parks. http://

www2.nature.nps.gov/air/pubs/pdf/gpra/

Gpra2005_Report_03202006_Final.pdf. (January 26, 2007).

U.S. Environmental Protection Agency [US EPA]. 1996a. Air quality criteria for

ozone and related photochemical oxidants. Section 4.0: Environmental concentrations, patterns, and exposure estimates. EPA/600/P-93/004aF. Washington,

DC: Office of Research and Development. Vol I.

U.S. Environmental Protection Agency [US EPA]. 1996b. Air quality criteria for

ozone and related photochemical oxidants. Section 5.0: Environmental effects

of ozone and related photochemical oxidants. EPA/600/P-93/004aF.

Washington, DC: Office of Research and Development. Vol II.

U.S. Environmental Protection Agency [US EPA]. 2006. Air quality criteria for

ozone and related photochemical oxidants (final). EPA/600/R-05/004aF-cF.

Washington, DC: Office of Research and Development.

Weinsten, D.A.; Laurence, J.A.; Retzlaff, W.A. [et al.]. 2005. Predicting the

effects of tropospheric ozone on regional productivity of ponderosa pine and

white fir. Forest Ecology and Management. 205: 73–89.
47

Ozone Injury in West Coast Forests: 6 years of Monitoring

Appendix 1: Biosite Index Calculation

The biosite index (BI) is the average score (amount x severity) for each species

averaged across all species on the biosite.

⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

= ∑ ∑

≥

= =

− −

10

1 1

1 1 1,000

n j

p

pj pj

m

j

j BI m n a s

where:

BI = biosite index,

m = number of species evaluated,

nj = number of plants of the j

th species evaluated,

apj = proportion of injured leaves on the p

th plant of the jth species, and

spj = average severity of injury on the p

th plant of the jth species.

Example: A BI is calculated for a biosite with 30 ponderosa pine trees, 30

mugwort plants, and 30 snowberry plants. Each plant of each species is evaluated

for amount and severity of ozone injury, with the following results:

Ponderosa pine: 28 trees with no injury (amount = 0; severity = 0); 1 tree with

amount = 2; severity = 2; 1 tree with amount = 2; severity = 5.

Mugwort: 29 plants with no injury (amount = 0; severity = 0); 1 plant with

amount = 3; severity =3.

Snowberry: 30 plants with no injury (amount = 0; severity = 0).

The midpoint of the amount or severity category is used to calculate BI. For

example, if the rating category is 2, then the value used is the midpoint of 0.07 to

0.25 = 0.16. The data, in tabular format, from the example biosite is listed below.

30 0 0 0

3 0 0 0

2 .16 0 0

1 0.16 0.38 0

Plant number Ponderosa pine Mugwort Snowberry

amount

M M M M

=
48

General Technical Report PNW-GTR-722

These data are then used to calculate BI as follows:

For each j species, the average amount x severity is calculated

Ponderosa pine: [(0.16 x 0.16) + (0.16 x 0.875) + (0 x 0) +...+ (0 x 0)] x 30-1

 =

0.0055

Mugwort: [(0.38 x 0.38) + (0 x 0) +...+ (0 x 0)] x 30-1 = 0.0048

Snowberry: [(0 x 0)+...+(0 x 0)] x 30-1 = 0

The average amount x severity for each species is then averaged across species and

multiplied by 1,000.

BI = 1,000(0.0055 + 0.0048 + 0.0) x 3-1 = 3.44

30 0 0 0

3 0 0 0

2 .875 0 0

1 0.16 0.38 0

Plant number Ponderosa pine Mugwort Snowberry

severity

M M M M

=
49

Ozone Injury in West Coast Forests: 6 years of Monitoring

Appendix 2: Ambient Ozone Exposure Indices

Calculation and Spatial Interpolation Methods1

Calculating Ambient Ozone Exposure Indices: Data Preparation

Ambient ozone data were downloaded from the U.S. Environmental Protection

Agency Technology Transfer Network Air Quality System Web site: http://

www.epa.gov/ttn/airs/airsaqs/archived%20data/downloadaqsdata.htm.

Ambient data were corrected for missing data by calculating a monthly average

for each hour for each site. If there is a missing monthly hour average (usually

because it is the hour that daily calibration checks are performed), it is estimated by

averaging the hour before and after as follows:

The monthly average for an hour was then added to the “corrected” table for

missing hours. Thus, the corrected table has an ozone value for every hour from

May 1 through September 30, unless an entire month of data was missing. In that

case, a monthly average cannot be calculated, because no data exist.

Calculating Ambient Ozone Exposure Indices: SUM60 12-Hour

Data Capture

The data capture (DC) is presented as a percentage of total hours between 08:00

and 20:00 in a month for which there are data. Data Capture = (number of values in

table per month per site) / (number of days in month x 12 hours)

( 1 1) 2

30

1

23

2

= − + + ÷ =

=

=

∫ ∑ Hour Hour

May th

Day May st

Hour

Hour

Hour

MonthlyAverage OzoneValue OzoneValue

( ) 2

30

1

= ∑ + ÷ =

Hour24 Hour2

May th

Day May st

MonthlyAverageHour1 OzoneValue OzoneValue

( ) 2

30

1

= ∑ + ÷ =

Hour1 Hour23

May th

Day May st

Monthly Average Hour24 OzoneValue OzoneValue

⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

÷⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛

∫ = ∑ ∑ ∑=

=

= =

−

−

Monthly Data Capture Count Ozone hours

Last Day in Month

Day

Hour

Hour

Last Day in Month

Day

Month

Month September

Month May

( ) 12 1

20

1 8

Excerpt from Prichard 2003.
50

General Technical Report PNW-GTR-722

Example:

If a site has 362 ozone values for May:

May DC = (362) / ( 31 x 12)

May DC = 97.3 percent

 The data captures for each month per site are averaged to calculate the data

capture for the 3-month and 5-month periods.

Only sites having 75 percent or greater original data capture have a SUM60

calculated. If the data capture is less than 75 percent, a null is reported for that site

and 5-month period for both the original and corrected data.

Calculating Ambient Ozone Exposure Indices: SUM60 Exposure

Index

The monthly, 3-month (June through August), and 5-month (May through

September) sum of all hourly ozone concentrations equaling or exceeding 60 parts

per billion (ppb) between 08:00 and 20:00 are calculated for each site in each of the

original tables and the corrected tables.

3 3

August

June

÷⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛ = ∑=

Month

Month

Month Data Capture Monthly DataCapture

5 5

September

May

÷⎟

⎟

⎠

⎞

⎜

⎜

⎝

⎛ = ∑=

Month

Month

Month Data Capture Monthly DataCapture

∫ ∑ ∑ = = =

= ≥

20

1 8

23

2

60 60

Hour

Last Day in Month

Month Day

SUM Month Ozone

3 60

20

8

August 30th

June1st

60 = ∑ ∑ ≥ = =Month Ozone

Day Hour

SUM

5 60

20

8

September 30th

May1st

60 = ∑ ∑ ≥ = =Month Ozone

Day Hour

SUM
51

Ozone Injury in West Coast Forests: 6 years of Monitoring

Spatial Interpolation of Ambient Ozone Exposure Indices

The inverse distance weighting scheme was selected based on previous experience

with spatial interpolation of ozone exposures. The power of the function was set to

2, indicating a monitor’s influence on a grid cell decreases with the square of

distance. The variable scheme was used with each grid cell being the composite of

the seven closest monitors. However, no monitor can be more than 500 kilometers

(310 miles) from a grid cell. Please note that a lack of good data in the Southern

United States led to having a restriction of no monitor farther than 700 kilometers

(435 miles) in 2001. Each grid cell is 3 kilometers (5.6 miles) square.

 Specifically, without the restriction on the distance, grid cells in data-sparse

regions can have values higher than expected. With a low number of monitors

versus the size of the region, it is not possible to interpolate based on a subset of

data and then verify the process with the remaining data.
52

General Technical Report PNW-GTR-722

Appendix 3: Ozone Injury Risk Assessment

Methods

We use a risk assessment approach that was suggested by Smith et al. (in press),

demonstrated by Coulston et al. (2003), and consistent with the ecological risk

assessment paradigm described by Regens (1995). Table 5 provides a quantitative

description of observed plant response to ambient ozone conditions (biosite index

[BI]), and a qualitative description of risk and possible impacts. However, plant

injury to bioindicator species from ozone is recorded on biosites, which are generally open areas that may or may not meet the Forest Inventory and Analysis (FIA)

requirements of forest land (land that is at least 10 percent stocked with live trees,

not currently developed for nonforest use, and larger than 1 acre and at least 120

feet wide) and use bioindicator species that may or may not be forest tree species.

Therefore to evaluate the likelihood of ozone injury to forest trees, we use spatial

interpolation to extend the information collected at biosites to the forest population

(Coulston et al. 2003; Smith et al., in press).

We interpolated gridded maps of the BI for each year 2000 through 2005 via

gradient inverse distance weighting (GIDS). The GIDS technique was first proposed

as a way to interpolate climatic data on a broad spatial scale as input for plant

growth models (Nalder and Wein 1998). The GIDS technique combines multiple

linear regression with inverse distance weighting interpolation and, like other

recently developed interpolation techniques, incorporates elevation as a covariate.

For a given unmeasured location k and variable Z, an ordinary least squares

regression is performed by using the N closest neighboring locations to calculate

coefficients (Cx

, Cy, and Ce) representing x, y, and elevation gradients: Z = a + Cx X

+ Cy

 Y + Ce E + ε ̃, where a is the intercept and ε is error. Then, the basic GIDS

formula is

( ) ( )( )

∑

∑

=

=

+ − + − + −

= N

i i

N

i i

i x k i y k i e k i

k

d

d

Z C X X C Y Y C E E

Z

1

2

1

2

1

where Zk = the predicted value at an unmeasured location k, Zi= the measured

value at location i, X = the x-coordinate for the specified location, Y = the y-coordinate, E = the elevation value, and d = the three-dimensional distance from measured

location i to k (Nalder and Wein 1998).
53

Ozone Injury in West Coast Forests: 6 years of Monitoring

For each location of interest, we fitted a generalized linear model, based on the

30 closest neighboring biosites. We acknowledged that all three gradient variables

(x, y, and elevation) could prove insignificant for a given prediction location and its

closest measured neighbors. As a result, we evaluated a sequence of the full and all

possible reduced models for statistical significance:

1. Z = a + Cx X + Cy Y + Ce E + ε,

2. Z = a + Cx

 X + Ce E + ε,

3. Z = a + Cy

 Y + Ce E + ε,

4. Z = a + Cx

 X + Cy Y + ε,

5. Z = a + Cx

 X + ε,

6. Z = a + Cy

 Y + ε,

7. Z = a + Ce

 E + ε.

For each prediction location, we tested all seven regression models by using the

30 closest stations and identified those models in which all variables were significant. In cases where more than one of the models had all significant variables, we

identified the one that yielded the smallest value for Akaike’s Information Criterion.

If the best-performing model was not the full model, then the coefficient(s) for any

insignificant variable(s) were set to zero in the GIDS equation. If none of the tested

models proved to have significant variables, then the GIDS interpolation reverted to

inverse distance squared weighting (i.e., all variable coefficients were set to zero).

The six interpolated BI maps were averaged to create the final risk map (fig. 11,

average 2000-2005 BI). We then overlaid the final risk map with FIA plots. This

variable (the 2000-2005 BI for each FIA plot) could then be used to summarize the

FIA survey data. At this point, we used the methods suggested by Bechtold and

Patterson (2005) to summarize the FIA data. For example, we estimated the number

of acres of forest land and the volume of susceptible tree species in each

BI risk category (table 10).
Pacific Northwest Research Station

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