United States

Department of

Agriculture

Forest Service

Southern 

Research Station

General Technical 

Report SRS–118

Ozone Injury Across the 

Southern United States, 

2002–06

Anita K. Rose and John W. Coulston
August 2009

Southern Research Station

200 W.T. Weaver Blvd.

Asheville, NC 28804

Authors 

Anita K. Rose is an Ecologist and John W. Coulston is a Supervisory 

Research Forester with the Forest Inventory and Analysis Research 

Work Unit, U.S. Forest Service, Southern Research Station, Knoxville, 

TN 37919.

Cover photos: Sweetgum, sassafras and yellow-poplar, three 

species known to be sensitive to ozone-induced foliar injury. Cover 

photos courtesy of Paul Wray, Iowa State University, Bugwood.org 

(yellow-poplar); and Chris Evans, River to River CWMA, 

Bugwood.org (sweetgum and sassafras).
Ozone Injury Across the Southern 

United States, 2002–06

Anita K. Rose and John W. Coulston
II

Abstract

In the Eastern United States, hourly concentrations of ozone typically range from 30 to 50 parts per billion (ppb), 

with events that may exceed 100 ppb. Typical exposure levels can cause visible foliar injury to some plant species 

and have the potential to reduce tree growth by up to 10 percent per year, depending on species and environment. 

As part of the Forest Service, U.S. Department of Agriculture, Forest Inventory and Analysis (FIA) Program, 

ozone-induced foliar injury is evaluated in the South between late July and mid-August on about 350 ozone 

biosites. For 2002 through 2006, ozone injury occurred on between 8 (2006) and 29 percent (2003) of the sampled 

biosites. South Carolina had the highest percentage of biosites with injury in 3 out of 5 years. The area at greatest 

risk from ozone injury occurred in northern Georgia. Both the moisture index and the combination of ozone 

exposure and moisture were significantly different for biosites where injury was observed and biosites where injury 

was not observed. This evidence suggests that, despite reported declines in ambient ozone concentrations over the 

past 10 years, some forest areas in the South were classified in the low and no risk categories due to the moisture 

deficit conditions that existed during the 2002-06 time period. The correlation between ozone injury and moisture 

conditions, as well as the consistent low to moderate levels of injury, occurring year after year in some parts of the 

South, warrant continued monitoring and close scrutiny for potential forest health impacts. FIA conducts the only 

annual nationwide systematic survey for ozone-induced foliar injury. This information is extremely valuable to 

research on trends in ozone exposure and injury and the impacts to vegetation across the United States. 

Keywords: Biomonitoring, FIA, forest health, indicator species, ozone.
III

CONTENTS

Highlights . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Study Area . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Field Methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Analyses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Biosites . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

Bioindicators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Ozone Exposure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13

Moisture Index . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Integration of Injury, Exposure, and Moisture . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Risk Assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17

Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23

Literature Cited . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24

Page

Highlights

Biomonitoring of ozone injury by FIA from 2002 through 

2006 in the South found the following:

• Ozone injury occurred on between 8 (2006) and 29 

percent (2003) of the biosites sampled.

• South Carolina had the highest percentage of biosites with 

injury in 3 out of 5 years.

• Foliar injury occurred most frequently on blackberry 

(Rubus allegheniensis), milkweed (Asclepias), 

and sweetgum (Liquidambar styraciflua).

• Both the moisture index (MI) and the combination of 

ozone exposure and moisture were significantly different 

(p < 0.001) for biosites where injury was observed and 

biosites where injury was not observed.

• An estimated 17.5 million acres of forest land and 20.4

billion cubic feet of susceptible tree volume were

classified in the low, moderate, and high risk categories.

• The area at greatest risk from ozone injury occurred in 

northern Georgia.

• Most of the forest area in the South was classified in the 

low or no risk categories.

Introduction

In the Eastern United States, hourly ambient concentrations 

of ozone typically range from 30 to 50 parts per billion 

(ppb), with events that may exceed 100 ppb (Chappelka and 

Samuelson 1998, U.S. Environmental Protection Agency 

2004, U.S. Environmental Protection Agency 2008). Typical 

exposure levels can cause visible foliar injury to some plant 

species and have the potential to reduce tree growth by up to 

10 percent per year, depending on species and environment 

(Chappelka and Samuelson 1998). Ozone is the product of 

chemical reactions that take place in the lower atmosphere 

when volatile organic compounds (VOCs) mix and react 

with nitrogen oxides (NOx) in the presence of sunlight. 

Anthropogenic emissions, primarily from the combustion 

of organic compounds (i.e. gasoline and coal), account for 

a large majority of NOx

 inputs to the environment (fig. 1). 

In contrast, VOCs come primarily from natural sources, 

such as trees and other vegetation, although some of the 

total inputs of VOCs do come from industrial and vehicular 

emissions. Weather plays a key role in the formation of 

ozone, with hot, dry, calm, cloudless days providing ideal 

conditions for VOCs and NOx to combine and react to form 

ozone (U.S. Environmental Protection Agency 2004).

Ozone exposure, uptake, and sensitivity all play important 

roles in the response of plants to ozone. Ozone exposure 

varies spatially and temporally. Weather patterns and 

changes in emissions of precursors account for a majority 

of year to year variations. Between 1970 and 2003, the 

VOC and NOx emissions that contribute to the formation of 

ground-level ozone decreased 54 percent and 25 percent, 

respectively (U.S. Environmental Protection Agency 2004). 

Motor

vehicles

56%

All other

5%

Industrial/

commercial

17%

Utilities

22%

Figure 1—NOX emissions by source category.

Ozone Injury Across the Southern 

United States, 2002–06

Anita K. Rose and John W. Coulston
2

General Technical Report SRS–118

Spatially, ozone exposure varies by topography, with higher 

elevations often having higher concentrations than lower, 

and more exposed sites having higher ozone than sheltered 

sites (Anderson and others 1988, Samuelson and Kelly 

2001). In addition, ozone concentrations are typically higher 

in open areas than within closed forests. Within forests, 

ozone concentrations are higher in the upper canopy than 

the lower, with lowest concentrations on the forest floor 

(Fredericksen and others 1995, Samuelson and Kelly 2001).

The uptake of ozone by plants depends upon many things, 

including physiological age, climate, and light availability. 

Instantaneous uptake rates of ozone tend to be higher in 

seedlings than mature trees, although cumulative uptake is 

higher in mature trees than in seedlings (Fredericksen and 

others 1995). Additionally, higher light availability in the 

upper canopy means higher ozone uptake than in the lower 

canopy. Site characteristics and available moisture also 

factor into the variability of ozone uptake (Bartholomay 

and others 1997, Peterson and others 1993, Samuelson 

and Kelly 2001). Dry conditions tend to decrease stomatal 

conductance, thereby lowering ozone uptake (Patterson and 

others 2000). However, there is some evidence that ozone 

can exacerbate drought stress in some trees by reducing root 

growth (Bartholomay and others 1997, McLaughlin and 

Downing 1996).

Sensitivity to ozone varies by species, genotype, 

physiological age, and leaf morphology. Several species, 

such as black cherry (Prunus serotina) and blackberry 

(Rubus allegheniensis), are known to be sensitive to ozone 

and exhibit a visible foliar response. There is some evidence 

that sensitivity can vary by genotype within a given species, 

with resistant strains showing little or no response compared 

to sensitive ones (Benoit and others 1982). This, in effect, 

could lead to reduced genetic diversity with sensitive strains 

being outcompeted by more resistant ones. Physiological 

age can also alter sensitivity, with seedlings being less 

sensitive to ozone than mature trees (Samuelson and 

Edwards 1993), although the reverse may be true for some 

species (Fredericksen and others 1995). Leaf morphology 

can alter the sensitivity of leaves on a given plant, with 

shade leaves being more sensitive than sun leaves, although, 

as noted, ozone concentrations tend to be higher in the upper 

canopy than the lower. In addition to the visible foliar injury 

exhibited by some species, reduced growth and decreased 

species richness have been reported from studies of ozone 

impacts to plants (Arbaugh and others 1998, Barbo and 

others 1998, Bartholomy and others 1997, McLaughlin 

and Downing 1996, Rebbeck 1996, Reinert and others 

1996, Samuelson and Edwards 1993, Somers and others 

1998). However, the effect of ozone on forest health is not 

fully understood due to the lack of studies showing direct 

relationships between foliar injury, uptake, and physiological 

response (Fredericksen and others 1995, Somers and others 

1998). Further confounding the ozone injury issue are the 

uncertainties surrounding the extrapolation of responses 

from controlled studies of seedlings to large forest trees 

(Samuelson and Kelly 2001). A review of the impacts of 

ozone on trees, including issues surrounding scaling treelevel responses to the landscape to determine ozone-induced 

effects, can be found in Bytnerowicz (2002), Chappelka 

and Samuelson (1998), Karnosky and others (2007), and 

Samuelson and Kelly (2001).

The objectives of this report are to: (1) describe ozone injury 

observed on Forest Inventory and Analysis (FIA) ozone 

biomonitoring sites from 2002 through 2006, (2) quantify 

ambient ozone concentrations from 2002 through 2006, (3) 

describe moisture conditions from 2002 through 2006, and 

(4) perform a risk assessment to elucidate areas at high risk 

of ozone impacts. 

Methods

Study Area

The study area for our analysis was an 11 State region in 

the South including Alabama, Arkansas, Florida, Georgia, 

Kentucky, Louisiana, North Carolina, South Carolina, 

Tennessee, Texas, and Virginia (fig. 2). Parts of Florida and 

Texas were excluded due to a lack of suitable biomonitoring 

locations and insufficient suitable species. Ozone injury data 

were not collected in Mississippi or Oklahoma during the 

2002–06 time period. In addition, ozone injury data were not 

collected in Louisiana in 2006.

Field Methods

As part of the Forest Service, U.S. Department of 

Agriculture FIA Program, ozone-induced foliar injury in the 

South is evaluated by field personnel between late July and 

mid-August (U.S. Department of Agriculture 2004). Ozone 

biomonitoring sites (biosites) are determined by using a 

national ozone triangular grid, separate from the regular FIA 

triangular plot grid. This grid allows for more closely spaced 

biosites in areas of higher potential ozone exposure (fig. 2). 

Within each cell of the grid, an ozone biosite is established 

using a set of criteria, such as access, size, and number of 

species (table 1).
3

Ozone Injury Across the Southern United States, 2002–06

Figure 2—Ozone biomonitoring program sampling polygons and study area (shaded), 2002–06. The intrastate borders for the shaded 

areas in Texas and Florida are the county boundaries.

Table 1—Site selection criteria for ozone injury assessments

Site First choicea Second choice

Access Easy Easy

Location Single location is used Two locations within 3 miles of each other, 

preferably with similar site conditions

Size of opening >3 acres (1.2 ha); wide open area; <50 

percent crown closure

Between 1 to 3 acres; long, narrow, or 

irregularly sized opening

Species count More than three species Two or more species

Plant count 30 plants of 3 species; 10 to 30 plants of 

additional species

30 plants of 2 species; 10 to 30 plants of 

additional species

Soil conditions Low drought potential; good fertility Moderately dry; moderate fertility

Site disturbance No recent (1 to 3 years) disturbance; no 

obvious soil compaction

Little or no disturbance; no obvious soil 

compaction

a Best site.
4

General Technical Report SRS–118

Once a biosite is established, at least 30 individuals of 

at least 2, preferably 3 or more, bioindicator species are 

examined for ozone injury (table 2). The key characteristic 

of bioindicator plants is that they respond to ambient 

levels of ozone with distinct foliar symptoms that are easy 

to diagnose. For example, bioindicator species, such as 

yellow-poplar (Liriodendron tulipifera) and sweetgum 

(Liquidambar styraciflua), exhibit an upper surface foliar 

injury symptom that can be readily distinguished from other 

foliar injuries (fig. 3). While ozone bioindicator species 

are considered highly sensitive, there can be variability 

among and within ozone bioindicator species. This is why 30 

observations from each of at least 2 bioindicator species are 

required, while 3 or more is preferable (82 percent of biosites 

between 2002 and 2006 had 3 or more species evaluated). 

Each plant is examined for amount of injury (percentage of 

leaves on a plant with injury) and severity (percentage of leaf 

area of injured leaves with ozone injury). For injury validation 

purposes, field personnel then collect three symptomatic 

leaves for each individual species at each biosite.

Analyses

Biosite index—For each biosite, a biosite index (BI) was 

calculated based upon the average score (amount as a 

proportion multiplied by severity as a proportion) for each 

species (the species index) averaged across all species on 

the biosite and then multiplied by 1,000 to allow categories 

to be defined by integers (Smith and others 2003). For 

mapping, interpretation, and risk analysis, the BI values 

were assigned to four categories based on Smith and others 

2003 (table 3). 

Ozone exposure—The Environmental Protection Agency 

(EPA) monitors hourly ambient ozone concentrations at 

266 locations distributed across the study area. We obtained 

these data as well as data for the surrounding States from 

the EPA for 2002–06. We then used the SUM06 index 

to summarize each ozone season. The SUM06 index is 

a commonly used method to summarize ambient ozone 

concentrations for a particular time period of interest (see 

Davis and Orendovici 2006 for example). It is the sum of 

all hourly ozone concentrations ≥ 0.06 parts per million 

(ppm). For our application we calculated the SUM06 index 

for a 12-hour period (8 a.m. to 8 p.m.) for June, July, and 

August for each year. Any monitoring station that had 

> 25 percent missing hourly observations was removed 

and monitoring stations that had ≤ 25 percent missing 

observations were adjusted based on EPA guidelines. We 

then created interpolated surfaces for SUM06 for each 

year using inverse distance squared weighting based on the 

12 nearest neighbors. We then summarized the land area 

in each of four classes (The H. John Heinz III Center for 

Science, Economics, and the Environment 2008) by year for 

comparison. The classes were: SUM06 ≤ 10, 10 < SUM06 

≤ 20, 20 < SUM06 ≤ 30, SUM06 > 30 ppm-hours per year. 

Table 2—Ozone bioindicator species for the Eastern United States

Type Common name Scientifi c namea b

Tree species

White ash Fraxinus americana L.

Sweetgum Liquidambar styracifl ua L.

Yellow-poplar Liriodendron tulipifera L.

Pin cherry Prunus pensylvanica L. f.

Black cherry P. serotina Ehrh.

Sassafras Sassafras albidum (Nutt.) Nees

Herbaceous species

Spreading dogbane Apocynum androsaemifolium L.

Common and tall milkweed Asclepias spp. L.

Bigleaf aster Eurybia macrophylla (L.) Cass.

Allegheny blackberry Rubus allegheniensis Porter

a

 Little (1979). 

b

 USDA Natural Resources Conservation Service (2006).

Table 3—Classifi cation scheme for the FIA ozone biosite index

Injury 

category 

 Biosite 

 index

Bioindicator

 response 

Risk 

assumption

1 0–4.9 Little or no injury No risk

2 5.0–14.9 Light to moderate injury Low risk

3 15.0–24.9 Moderate to severe injury Medium risk

4 ≥25 Severe foliar injury High risk

FIA = Forest Inventory and Analysis.
5

Ozone Injury Across the Southern United States, 2002–06

Figure 3—Ozone injury symptoms on (A) yellow-poplar (photo courtesy of U.S. Forest Service, Region 8, Bugwood.org), (B) black 

cherry, and (C) blackberry (B and C photos courtesy of Gretchen Smith).

(A) Yellow-poplar

(B) Black cherry (C) Blackberry

Moisture index—To examine the potential moisture 

available to plants from 2002 to 2006 within our study area 

we used a moisture index (MI) based on precipitation and 

potential evapotranspiration (PET) (Akin 1991, Coulston 

and Riitters 2005, Koch and others, in press). Parameterelevation Regression on Independent Slopes (PRISM) 

climate mapping system data served as the basis for these 

maps. The PRISM system is knowledge-based, integrating 

a localized climate-elevation regression function with other 

algorithmic components: station weighting, topographic 

facets, coastal proximity, and a two-layer atmosphere 

(Daly and others 2002). In the case of precipitation, the 

PRISM product was used directly. PET was calculated 

using Thornthwaite’s (1948) model as described in Akin 

(1991). The PRISM temperature data was used to implement 

Thornthwaite’s model. We then used a modified MI 
6

General Technical Report SRS–118

were weighted more heavily than those that represented less 

land area. Also, because the MI and the SUM06 index were 

measured on different scales, we standardized each variable 

to a mean of zero and a variance of one.

Risk assessment—Foliar injury is surveyed to determine 

where negative impacts to forest trees may be occurring. 

Monitoring foliar injury of bioindicator plants does not 

identify specific levels of ozone present, but rather identifies 

whether conditions were favorable for ozone injury to occur 

(Coulston and others 2003). Although correlations between 

high levels of ozone exposure and foliar injury have been 

observed (Hildebrand and others 1996, Smith and others 

2003), strong relationships between ozone exposure and tree 

responses have been difficult to confirm (Chappelka and 

Samuelson 1998). 

In order to develop risk assessment maps and evaluate 

the likelihood of ozone injury to forests, biosite indices 

were spatially interpolated using inverse distance squared 

weighting, a standard interpolation technique by which 

ozone risk is modeled for all unmeasured locations utilizing 

weighted averages from measured biosites (Smith and others 

2007). The 5 yearly maps were then averaged to create the 

5-year map of ozone risk. Averaging of biosite scores over a 

period of several years gives a clearer picture of the potential 

for foliar injury in a given location. Overlaying this map 

with FIA data allowed us to estimate the volume of sensitive 

tree species at risk of ozone injury and the area of forest land 

at risk of ozone injury using the standard FIA compilation 

methods presented in Bechtold and Patterson (2005). Each 

tree species measured on each FIA forest mensuration plot 

(FIA plot) was assigned a sensitivity ranking (sensitive, 

moderately sensitive, insensitive, or unknown) based on the 

literature review provided by Smith and others (2007). 

Results

Biosites

Every year over the 5-year study period, between 26,695 

and 30,897 bioindicator plants on 316 to 359 biosites were 

evaluated for ozone-induced foliar injury. The number of 

biosites with ozone-induced foliar injury varied between 27 

(8 percent) in 2006 and 93 (29 percent) in 2003 (table 4). 

In 2002 and 2003 between 5 and 6 percent of biosites were 

in categories 3 and 4, while in 2004 and 2006 only about 1 

percent of biosites were in categories 3 and 4 (table 5). 

In every year except 2006, South Carolina had foliar injury 

(Willmott and Feddema 1992) to examine the ratio 

of precipitation to PET, which bounds the ratio between 

-1 and 1.

P/PET–1, P < PET

1–PET/ P, P ≥ PET

0 , P = PET= 0

MI =

where

 MI = Moisture index

 P = Precipitation

 PET = Potential evapotranspiration measure in the same 

 units as P

We calculated MI for June, July, and August for each of the 

5 years (2002–06). We then summarized the land area in 

each of three classes, corresponding to moisture deficit (MI 

≤ -0.15), approximate moisture balance (-0.15 < MI ≤ 0.15), 

and moisture surplus (MI > 0.15) by year for comparison.

Integration of injury, exposure, and moisture—To 

examine the potential relationship among ozone induced 

foliar injury, ambient ozone, and moisture we overlayed the 

biosites with the SUM06 maps and MI maps. We then used 

Hotelling’s T2

 test and 95 percent Bonferroni simultaneous 

confidence intervals (Johnson and Wichern 2002) to examine 

potential significant differences in mean response vectors 

between biosites without injury (BI = 0) and those with 

injury (BI > 0). The null hypothesis was 















 















−















 0

06 06 0

0

0

0 MI

SUM

MI

SUM H

i

i

where 

 i = biosites with injury 

 0 = biosites without injury

Hotelling’s test is a common multivariate statistical 

technique which accounted for the correlation between 

ambient ozone concentrations and the MI (r = 0.62). When 

using these tests we had to account for the fact that the 

ozone biomonitoring survey is not an equal probability 

sample. To accomplish this, each observation was weighted 

proportional to the area of the polygon from figure 2 where 

the biosite resides. Biosites that represent more land area 
7

Ozone Injury Across the Southern United States, 2002–06

Table 4—Number of evaluated biosites with ozone-induced 

foliar injury by year and State

State

Year

2002 2003 2004 2005 2006

number

Alabama 

Evaluated 25 32 32 34 34

Injured 0 0 0 3 0

Arkansas 

Evaluated 25 25 24 24 24

Injured 0 4 6 0 0

Florida 

Evaluated 18 22 23 23 23

Injured 1 0 0 0 0

Georgia 

Evaluated 45 45 45 45 45

Injured 15 19 10 13 0

Kentucky 

Evaluated 31 29 23 37 38

Injured 10 17 9 3 4

Louisiana 

Evaluated 21 21 21 20 —

Injured 0 0 0 0 —

North Carolina

Evaluated 42 29 46 46 46

Injured 10 14 10 6 14

South Carolina

Evaluated 29 30 30 26 26

Injured 14 17 16 14 4

Tennessee 

Evaluated 39 37 40 40 40

Injured 7 13 5 4 3

Texas 

Evaluated 17 18 28 25 21

Injured 3 1 0 0 0

Virginia 

Evaluated 24 32 39 39 38

Injured 1 8 5 0 2

Total

Evaluated 316 320 351 359 335

Injured 61 93 61 43 27

— = no sample for the cell.

on 48 to 57 percent of biosites. South Carolina also had 

the highest percentage of biosites with injury in 2002, 

2004, and 2005. In 2003 and 2006, Kentucky and North 

Carolina, respectively, had the highest percentage of biosites 

with injury. In 2002, 2003, and 2005 South Carolina had 

the highest percentage of biosites in categories 3 and 4 

(table 6). In 2004 and 2006, Arkansas and Kentucky, 

respectively, had the highest percentage of biosites in 

categories 3 and 4. Florida, Louisiana, and Texas did not 

have any biosites in category 2 and higher in any year. 

Alabama and Arkansas did not have any biosites in category 

2 or higher in 4 out of 5 years.

In Georgia and South Carolina, the distribution of biosites 

with injured plants was fairly consistent from year to year, 

with the exception of 2006 (figs. 4 through 8). Injury was 

typically detected near Columbia and the GreenvilleSpartanburg area, and sometimes along the coast in 

South Carolina. In Georgia, the injury often occurred in 

areas surrounding Atlanta, Athens, and Macon. In North 

Carolina, ozone injury was often detected surrounding the 

Charlotte and Winston-Salem areas. The injury detected 

in Virginia typically occurred in the coastal region, and in 

the southwest portion of the State. Very often there was 

a line of injury in northwest Kentucky, around Lexington 

and Louisville, that in some years extended down to the 

northwest corner of Tennessee (as in 2003), or to the 

northeast corner of Arkansas (as in 2004). Another area 

with injury occurred in east Tennessee. In 2003 this area 

extended from Chattanooga northward along the border with 

North Carolina into southwest Virginia. A similar pattern 

existed in 2005, although with less injury and without the 

Table 5—Number and percentage of biosites in each biosite 

index category in the South, by year

Injury 

category a

Year

2002 2003 2004 2005 2006

1 Number 282 270 331 328 326

Percent 89.2 84.4 94.3 91.4 97.3

2 Number 17 32 16 15 6

Percent 5.4 10.0 4.6 4.2 1.8

3 Number 8 8 2 6 2

Percent 2.5 2.5 0.6 1.7 0.6

4 Number 9 10 2 10 1

Percent 2.8 3.1 0.6 2.8 0.3

a For corresponding biosite index values, response, and risk assumptions 

see table 3.
8

General Technical Report SRS–118

Year and State

Injury categorya

1 2 3 4

percentage

2002

Alabama 100.0 0.0 0.0 0.0

Arkansas 100.0 0.0 0.0 0.0

Florida 100.0 0.0 0.0 0.0

Georgia 82.2 11.1 2.2 4.4

Kentucky 87.1 6.5 3.2 3.2

Louisiana 100.0 0.0 0.0 0.0

North Carolina 85.7 7.1 4.8 2.4

South Carolina 69.0 10.3 6.9 13.8

Tennessee 84.6 7.7 5.1 2.6

Texas 100.0 0.0 0.0 0.0

Virginia 95.8 4.2 0.0 0.0

2003

Alabama 100.0 0.0 0.0 0.0

Arkansas 100.0 0.0 0.0 0.0

Florida 100.0 0.0 0.0 0.0

Georgia 73.3 15.6 6.7 4.4

Kentucky 79.3 10.3 3.4 6.9

Louisiana 100.0 0.0 0.0 0.0

North Carolina 86.2 13.8 0.0 0.0

South Carolina 46.7 33.3 6.7 13.3

Tennessee 81.1 16.2 2.7 0.0

Texas 100.0 0.0 0.0 0.0

Virginia 84.4 6.3 3.1 6.3

2004

Alabama 100.0 0.0 0.0 0.0

Arkansas 91.7 0.0 4.2 4.2

Florida 100.0 0.0 0.0 0.0

Georgia 91.1 6.7 0.0 2.2

Kentucky 78.3 21.7 0.0 0.0

Louisiana 100.0 0.0 0.0 0.0

Year and State

Injury categorya

1 2 3 4

percentage

2004 (continued)

North Carolina 97.8 2.2 0.0 0.0

South Carolina 73.3 23.3 3.3 0.0

Tennessee 100.0 0.0 0.0 0.0

Texas 100.0 0.0 0.0 0.0

Virginia 100.0 0.0 0.0 0.0

2005

Alabama 97.1 2.9 0.0 0.0

Arkansas 100.0 0.0 0.0 0.0

Florida 100.0 0.0 0.0 0.0

Georgia 73.3 13.3 4.4 8.9

Kentucky 97.3 2.7 0.0 0.0

Louisiana 100.0 0.0 0.0 0.0

North Carolina 93.5 0.0 4.3 2.2

South Carolina 57.7 15.4 7.7 19.2

Tennessee 92.5 7.5 0.0 0.0

Texas 100.0 0.0 0.0 0.0

Virginia 100.0 0.0 0.0 0.0

2006

Alabama 100.0 0.0 0.0 0.0

Arkansas 100.0 0.0 0.0 0.0

Florida 100.0 0.0 0.0 0.0

Georgia 100.0 0.0 0.0 0.0

Kentucky 92.1 2.6 5.3 0.0

Louisiana — — — —

North Carolina 95.7 4.3 0.0 0.0

South Carolina 92.3 7.7 0.0 0.0

Tennessee 95.0 2.5 0.0 2.5

Texas 100.0 0.0 0.0 0.0

Virginia 100.0 0.0 0.0 0.0

— = no sample for the cell.

a

 For corresponding biosite index values, response, and risk assumptions see table 3.

Table 6—Percentage of biosites by injury category, year, and State
9

Ozone Injury Across the Southern United States, 2002–06

Knoxville

Lexington Louisville

Clarksville

Chattanooga

Nashville

Huntsville

Birmingham

Mobile

Montgomery

Columbus

Tallahassee

Macon

Athens

Atlanta Augusta

Columbia

Savannah

Winston-Salem

Charleston

Charlotte

Greensboro Durham

Raleigh

Fayetteville

Hampton

Richmond

Newport News Norfolk

Portsmouth

Arlington

Alexandria

Orlando

Jacksonville

Clearwater Tampa

Cape Coral

St. Petersburg

Miami

Hialeah Hollywood

Coral Springs

Jackson

Little Rock

Memphis

Metairie Lafayette

New Orleans

Baton Rouge

Shreveport

Houston Beaumont

Pasadena

Plano

Dallas

Garland

Mesquite

Biosite index

0–4.9

5–14.9

15–24.9

> 24.9

No injury

Figure 4—Ozone biosites and biosite index, 2002.
10

General Technical Report SRS–118

Knoxville

Lexington

Louisville

Clarksville

Chattanooga

Nashville

Huntsville

Birmingham

Mobile

Montgomery

Columbus

Tallahassee

Macon

Atlanta Athens

Augusta

Columbia

Savannah

Winston-Salem

Charleston

Charlotte

Greensboro Durham

Raleigh

Fayetteville

Hampton

Richmond

Newport News Norfolk

Portsmouth

Arlington

Alexandria

Orlando

Jacksonville

Clearwater Tampa

Cape Coral

St. Petersburg

Miami

Hialeah Hollywood

Coral Springs

Jackson

Little Rock

Memphis

Metairie Lafayette

New Orleans

Baton Rouge

Shreveport

Houston Beaumont

Pasadena

Plano

Dallas Garland

Mesquite

Biosite index

0–4.9

5–14.9

15–24.9

> 24.9

No injury

Figure 5—Ozone biosites and biosite index, 2003.
11

Ozone Injury Across the Southern United States, 2002–06

Knoxville

Lexington Louisville

Clarksville

Chattanooga

Nashville

Huntsville

Birmingham

Mobile

Montgomery

Columbus

Tallahassee

Macon

Athens

Atlanta Augusta

Columbia

Savannah

Winston-Salem

Charleston

Charlotte

Greensboro Durham

Raleigh

Fayetteville

Hampton

Richmond

Newport News Norfolk

Portsmouth

Arlington

Alexandria

Orlando

Jacksonville

Clearwater Tampa

Cape Coral

St. Petersburg

Miami

Hialeah Hollywood

Coral Springs

Jackson

Little Rock

Memphis

Metairie Lafayette

New Orleans

Baton Rouge

Shreveport

Houston Beaumont

Pasadena

Plano

Dallas

Garland

Mesquite

Biosite index

0–4.9

5–14.9

15–24.9

> 24.9

No injury

Figure 6—Ozone biosites and biosite index, 2004.
12

General Technical Report SRS–118

Knoxville

Lexington Louisville

Clarksville

Chattanooga

Nashville

Huntsville

Birmingham

Mobile

Montgomery Columbus

Tallahassee

Macon

Athens

Atlanta Augusta

Columbia

Savannah

Winston-Salem

Charleston

Charlotte

Greensboro Durham

Raleigh

Fayetteville

Hampton

Richmond

Newport News Norfolk

Portsmouth

Arlington

Alexandria

Orlando

Jacksonville

Clearwater Tampa

Cape Coral

St. Petersburg

Miami

Hialeah

Hollywood

Coral Springs

Jackson

Little Rock

Memphis

Metairie Lafayette

New Orleans

Baton Rouge

Shreveport

Houston Beaumont

Pasadena

Plano

Dallas

Garland

Mesquite

Biosite index

0–4.9

5–14.9

15–24.9

> 24.9

No injury

Figure 7—Ozone biosites and biosite index, 2005.

extension into southwest Virginia. The relatively small 

amount of injury that was detected in Arkansas occurred in 

the northeastern portion of the State, as in 2003 and 2004.

Bioindicators

Although the percentage of biosites with injury was 

relatively high in certain years and States, only between 1 

percent and 3 percent of all evaluated plants had any injury 

(table 7). As was the case for biosites, the highest percentage 

of plants with injury occurred in 2003 (3 percent), and the 

lowest in 2006 (0.6 percent). Ozone-induced foliar injury 

was found most frequently on blackberry, milkweed, and 

sweetgum. No injury was found in any year on big leaf aster 

(Eurybia macrophylla) or pin cherry (Prunus pensylvanica), 

but note the small sample size (table 7). Very little injury 

was found in any year on black cherry and sassafras 

(Sassafras albidum). In 2002, a year of relatively high 

injury, 6 percent of all evaluated sweetgum and 4 percent 

of all milkweed had injury. In 2003, another year of high 
13

Ozone Injury Across the Southern United States, 2002–06

Knoxville

Lexington Louisville

Clarksville

Chattanooga

Nashville

Huntsville

Birmingham

Mobile

Montgomery Columbus

Tallahassee

Macon

Atlanta Athens

Augusta

Columbia

Savannah

Winston-Salem

Charleston

Charlotte

Greensboro Durham

Raleigh

Fayetteville

Hampton

Richmond

Newport News Norfolk

Portsmouth

Arlington

Alexandria

Orlando

Jacksonville

Clearwater Tampa

Cape Coral

St. Petersburg

Miami

Hialeah Hollywood

Coral Springs

Jackson

Little Rock

Memphis

Metairie Lafayette

New Orleans

Baton Rouge

Shreveport

Houston

Beaumont

Pasadena

Plano

Dallas Garland

Mesquite

Biosite index

0–4.9

5–14.9

15–24.9

> 24.9

No injury

Figure 8—Ozone biosites and biosite index, 2006.

injury, 7 percent of all evaluated blackberry and 9 percent of 

all milkweed had injury. Blackberry had the highest 5-year 

average species index, followed by milkweed and sweetgum 

(fig. 9). Bioindicator species were not sampled equally. 

Blackberry and sweetgum accounted for over one-half of 

plants evaluated every year (fig. 10). In addition, species 

were not sampled equally across States. For example, 

in 2002, sassafras accounted for 31 percent of all plants 

evaluated for ozone injury in Texas; in Arkansas, however, it 

only accounted for 7 percent. Likewise, in 2004, sweetgum 

accounted for 29 percent of plants evaluated in Alabama, but 

only for 7 percent in Kentucky. 

Ozone Exposure

Ambient ozone concentrations in the South were 

interpolated to create a continuous surface and then 

summarized in four categories: SUM06 ≤ 10, 10 < SUM06 

≤ 20, 20 < SUM06 ≤ 30, SUM06 > 30 ppm-hours per year. 

The concentrations varied both spatially and temporally. 
14

General Technical Report SRS–118

Table 7—Number of plants evaluated and injured by species and year 

Species 

Year

2002 2003 2004 2005 2006

number a

Big leaf aster

Evaluated 10 12 30 30 —

Injured 0 (0%) 0 (0%) 0 (0%) 0 (0%) —

Black cherry

Evaluated 4,262 4,540 4,312 4,291 4,150

Injured 0 (0%) 24 (0.5%) 0 (0%) 4 (0.1%) 0 (0%)

Blackberry

Evaluated 8,347 9,013 9,582 8,932 9,109

Injured 222 (2.7%) 659 (7.3%) 250 (2.6%) 269 (3.0%) 89 (1.0%)

Dogbane

Evaluated 370 370 403 703 1,180

Injured 1 (0.3%) 6 (1.6%) 2 (0.5%) 0 (0%) 6 (0.5%)

Milkweed

Evaluated 740 956 1,461 1,310 1,243

Injured 33 (4.5%) 90 (9.4%) 42 (2.9%) 8 (0.6%) 14 (1.1%)

Pin cherry

Evaluated — — 352 70 30

Injured — — 0 (0%) 0 (0%) 0 (0%)

Sassafras

Evaluated 2,714 3,245 3,298 3,413 2,598

Injured 4 (0.1%) 0 (0%) 0 (0%) 0 (0%) 0 (0%)

Sweetgum

Evaluated 6,155 6,594 6,950 6,331 6,464

Injured 361 (5.9%) 40 (0.6%) 61 (0.9%) 46 (0.7%) 51 (0.8%)

White ash

Evaluated 1,356 1,012 1,168 1,152 1,288

Injured 0 (0%) 19 (1.9%) 3 (0.3%) 0 (0%) 0 (0%)

Yellow-poplar

Evaluated 2,741 3,234 3,341 3,005 3,009

Injured 7 (0.3%) 36 (1.1%) 5 (0.1%) 6 (0.2%) 1 (0.0%)

Total

Evaluated 26,695 28,976 30,897 29,237 29,071

Injured 628 (2.4%) 874 (3.0%) 363 (1.2%) 333 (1.1%) 161 (0.6%)

— = no sample for the cell.

a

 Values in parentheses represent percentage of plants evaluated.
15

Ozone Injury Across the Southern United States, 2002–06

Figure 9—Average species index by year.

Species

Average species index

0

2

4

6

8

10

12

2002 2003 2004 2005 2006 Average 

Black 

cherry

BlackberryDogbaneMilkweedSassafrasSweetgumWhite 

ash

Yellowpoplar

Year

2002 2003 2004 2005 2006

Percentage of plants evaluated

0

10

20

30

40

50

60

70

80

90

100

Blackberry 

Sweetgum

Black cherry 

Yellow-poplar 

Sassafras 

Milkweed 

White ash 

Other*

Figure 10—Percentage of plants evaluated each year represented by 

species. * Other = dogbane, pin cherry, and big leaf aster.
16

General Technical Report SRS–118

SUM06 ≤ 10 FIA survey units

10 < SUM06 ≤ 20

20 < SUM06 ≤ 30

SUM06 > 30

Mean SUM06

Figure 11—Average 3-month growing season SUM06 values for the study area, 2002–06.

The highest average (2002–06) 3-month growing season 

SUM06 value was observed in North Carolina (fig. 11). 

Areas of relatively high SUM06 values (> 20 ppm-hours 

per year) were also observed in northern Georgia, east and 

west Tennessee, eastern Texas, east Arkansas, and through 

the piedmont of North Carolina and Virginia. Most of 

the land area in the South had average 3-month growing 

season SUM06 values < 20 ppm-hours per year. The lowest 

values of SUM06 were generally observed in Florida and 

Louisiana. However, there was temporal variation in the 

proportion of land in each category. In 2002, there were 

relatively equal amounts of land area in each category, 

which was in sharp contrast to 2004, when nearly 100 

percent of the land area had concentrations < 20 ppm-hours 

per year (fig. 12). 
17

Ozone Injury Across the Southern United States, 2002–06

Moisture Index

On average, from 2002 to 2006, most of the land area in the 

South was classified as having a moisture deficit (MI 

≤ -0.15) during the 3-month (June, July, and August) 

growing season (fig. 13). However, during this time period, 

moisture balance or surplus (MI > -0.15) was observed 

along the Atlantic Coastal Plain and in the Southern 

Appalachians. There also was temporal variation in the 

MI from 2002 to 2006. The driest growing seasons were 

observed in 2002 and 2006, where about 80 percent of the 

land area was classified as having a moisture deficit (fig. 14). 

The greatest proportion of land (about 0.27) with a moisture 

surplus (MI > 0.15) occurred in 2003. 

Integration of Injury, Exposure, and Moisture

Across years, biosites where injury was observed generally 

had a higher MI value and a higher SUM06 value. The 

average SUM06 value for biosites where injury was not 

observed was 12.85 ppm-hours while biosites where injury 

was observed was 13.47 ppm-hours (but this difference was 

not significant). The average MI for biosites where injury 

was not observed was -0.198 (moisture deficit category) 

while the average MI was -0.082 (approximate moisture 

balance) for biosites where injury was observed. The null 

hypothesis for the Hotelling T2

 test was rejected (p < 0.001) 

and we provisionally accepted the alternative hypothesis 

that there was a difference between mean response vectors 

for biosites where injury was observed versus biosites 

where injury was not observed. We then examined the 

simultaneous 95 percent Bonferroni confidence intervals to 

identify whether a single variable was significant. Because 

the 95 percent Bonferroni confidence intervals for the 

MI did not contain zero, the MI contributed significantly 

toward explaining the difference between mean response 

vectors (fig. 15). The highest percentage of biosites with 

injury occurred in 2003, the only year when SUM06 values 

were > 10 ppm-hours on over 50 percent of the land area 

and nearly 75 percent of the land area was in a moisture 

surplus or balance. In contrast, the year 2002, which had the 

second highest amount of injury, was a rather dry year, with 

about 80 percent of the land area having a moisture deficit. 

However, this was the only year where almost 30 percent of 

the land area saw exposures between 20 and 30 ppm-hours, 

and another 26 percent had SUM06 values > 30 ppm-hours. 

Even in years with relatively low ozone exposure, as in 

2004 (SUM06 values on nearly 70 percent of the land area 

were < 10 ppm-hours), the high degree of moisture surplus 

and balance likely contributed to 17 percent of sites having 

injury.

Risk Assessment

Overall, about 163.0 million acres of forest land (90 percent) 

in the South was classified in the no risk category (BI 

< 5) (table 8). The lowest risk category also contained about 

90 percent of the tree volume in the South (table 9). The 

average BI for sensitive species was < 5, which indicates 

that there was not a potential regional ozone issue for a 

particular sensitive species. While most of the forest land in 

the South had no risk of ozone injury, 17.5 million acres of 

forest land were classified in the low (BI 5–14.9), moderate 

(BI 15–24.9), and high (BI ≥ 25) risk categories (table 8). 

Within the low, moderate, and high risk forest areas, about 

20.3 billion cubic feet of tree volume was from sensitive 

species (table 9). The area at greatest risk from ozone injury 

occurred in northern Georgia (fig. 16) where about 21,914 

acres of forest were classified in the high-risk category 

(table 8). Within this high risk area moderately sensitive 

and sensitive species accounted for about 58 percent of the 

tree volume. 

Year

2002 2003 2004 2005 2006

Proportion of land area

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8 SUM06 ≤ 10 

10 < SUM06 ≤ 20

20 < SUM06 ≤ 30

SUM06 > 30

Figure 12—The proportion of land area in each SUM06 category by 

year.
18

General Technical Report SRS–118

MI ≤ -0.15 FIA survey units

-0.15 < MI ≤ 0.15

MI > 0.15

Mean moisture index (MI)

Figure 13—Average 3-month growing season moisture index for the study area, 2002–06.
19

Ozone Injury Across the Southern United States, 2002–06

Year

2002 2003 2004 2005 2006

Proportion of land area

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

Deficit Average Surplus 

Figure 14—The proportion of land area in each moisture index 

category by year.

Response vector

Moisture index SUM06 (ppm)

Average difference -0.2

-0.1

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

Figure 15—The average difference between biosites with 

and without injury by response vector. Ninety-five percent 

Bonferroni simultaneous confidence intervals are 

indicated by the vertical lines.

Table 8—Estimated area of forest land by biosite index and risk category by 

State, 2002–06

State

Biosite indexa

0 to 4.9

(no risk)

5.0 to 14.9 

(low risk)

15.0 to 24.9 

(moderate risk)

≥ 25

(high risk)

acres

Alabama 22,566,073 0 0 0

Arkansas 18,271,773 131,880 0 0

Florida 15,037,406 0 0 0

Georgia 19,228,395 5,426,306 262,482 21,914

Kentucky 11,822,577 307,210 0 0

Louisianab 14,138,135 0 0 0

North Carolina 16,980,241 1,615,518 0 0

South Carolina 3,551,265 9,342,953 0 0

Tennessee 13,936,824 14,807 0 0

Texas 12,129,663 0 0 0

Virginia 15,337,078 421,312 0 0

Total 162,999,432 17,259,984 262,482 21,914

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

b

 2002–05.
20

General Technical Report SRS–118

Table 9—Estimated volume of live trees, by biosite index and risk category, by State, 

and ozone-sensitivity category, 2002–06

State and ozonesensitivity categorya

Biosite indexb

0 to 4.9

(no risk)

5.0 to 14.9

(low risk)

15.0 to 24.9

(moderate risk)

≥ 25

(high risk)

million cubic feet

Alabama

Unknown 11,649.53

Insensitive 1,714.17

Moderately sensitive 2,434.30

Sensitive 16,558.33

Arkansas

Unknown 9,292.95 286.90

Insensitive 3,722.19 4.04

Moderately sensitive 5,051.03 5.43

Sensitive 9,226.22 71.60

Florida

Unknown 15,487.38

Insensitive 28.98

Moderately sensitive 105.08

Sensitive 3,169.31

Georgia

Unknown 14,030.55 2,069.44 98.97 10.89

Insensitive 919.07 1,001.77 55.26 10.06

Moderately sensitive 1,279.41 1,082.25 46.99 1.19

Sensitive 11,950.25 6,290.49 328.15 27.46

Kentucky

Unknown 7,667.04 217.73

Insensitive 5,015.92 99.49

Moderately sensitive 2,611.13 25.13

Sensitive 6,832.82 167.84

Louisianac

Unknown 10,560.39

Insensitive 505.21

Moderately sensitive 867.64

Sensitive 10,404.32

North Carolina

Unknown 8,499.58 709.82

Insensitive 3,802.02 169.97

Moderately sensitive 2,369.76 258.16

Sensitive 19,423.72 1,426.90

South Carolina

Unknown 2,393.20 4,184.45

Insensitive 153.24 893.06

Moderately sensitive 191.47 753.31

Sensitive 3,818.57 9,298.64

Tennessee

Unknown 10,087.02 8.74

Insensitive 5,393.14 4.10

Moderately sensitive 3,410.90 4.97

Sensitive 9,241.75 18.12

continued
21

Ozone Injury Across the Southern United States, 2002–06

Table 9—Estimated volume of live trees, by biosite index and risk category, by State, 

and ozone-sensitivity category, 2002–06 (continued)

State and ozonesensitivity categorya

Biosite indexb

0 to 4.9

(no risk)

5.0 to 14.9

(low risk)

15.0 to 24.9

(moderate risk)

≥25

(high risk)

million cubic feet

Texas

Unknown 6,099.80

Insensitive 397.55

Moderately sensitive 1,776.17

Sensitive 9,280.33

Virginia

Unknown 7,216.67 308.49

Insensitive 5,220.88 262.50

Moderately sensitive 2,888.90 109.95

Sensitive 15,726.05 435.24

All States

Unknown 102,984.12 7,785.58 98.97 10.89

Insensitive 26,872.37 2,434.93 55.26 10.06

Moderately sensitive 22,985.79 2,239.18 46.99 1.19

Sensitive 115,631.67 17,708.82 328.15 27.46

Total 268,473.95 30,168.52 529.37 49.60

a Ozone-sensitivity categories are based on both fi eld observations and fumigation trials (Smith and 

others 2007).

b Biosite index based on interpolated values for each Forest Inventory and Analysis plot.

c

 2002–05.
22

General Technical Report SRS–118

BI < 5 FIA survey units

5 ≤ BI <15

15 ≤ BI < 25

BI ≥ 25

Mean biosite index (BI)

Figure 16—Average biosite index for the study area, 2002–06.
23

Ozone Injury Across the Southern United States, 2002–06

Discussion

The U.S. Environmental Protection Agency (2008) has 

reported a general decline of 13 percent in levels of ambient 

ozone across the South over the past 10 years, but, this 

decline has been spatially variable. Kentucky, Tennessee, 

and North Carolina had ozone declines between 12 and 16 

percent while South Carolina and Georgia only had declines 

of 4 and 9 percent, respectively. Despite overall declines in 

ambient ozone concentrations, ozone induced foliar injury 

still occurs in the South, particularly in Georgia and South 

Carolina. 

The incidence of foliar injury varied both spatially and 

temporally. When the amount and severity of injury recorded 

on biosites was averaged across all 5 years, most of the 

forest area in the South was classified in the low or no risk 

category (table 8). While this seems to indicate that there 

is not currently a regional ozone forest health issue, this is 

complicated by the fact that a majority of the South was in a 

moisture deficit during the 2002-06 time period. There was 

an area of relatively high risk identified in northern Georgia. 

This area may be a candidate for a followup investigation 

to determine whether there is an actual forest health 

issue. While South Carolina did not stand out as being at 

particularly high risk for ozone injury, only 28 percent of 

the forest land in that State was in the no risk category, 

the lowest for any State. In addition, for 2002 through 

2006, 40 percent of the 10 highest BI values in the South 

were in South Carolina. These consistent low to moderate 

levels of injury occurring year after year warrant continued 

monitoring and close scrutiny for potential forest health 

impacts. Further research is also needed to relate foliar 

injury to responses at individual tree species, ecosystem, and 

regional levels.

Numerous studies describe the importance of moisture 

availability in determining whether ozone injury occurs (see 

for example, Davis and Orendovici 2006, Smith and others 

2003). In fact, the importance of spatial and interannual 

moisture availability may explain why strong relationships 

between ozone exposure and injury have not been 

documented in the Southern United States (Chappelka and 

Samuelson 1998). From the integrated analysis, (Integration 

of Injury, Exposure, and Moisture section) we infer that 

ozone exposures in the South are generally high enough 

to injure bioindicator plants and it is the co-occurrence 

of sufficient moisture availability that is actually a more 

important driver in determining whether injury occurs. This 

theory is supported by our findings that ozone exposure 

did not differ significantly between biosites with injury and 

those without, while both moisture alone and the interaction 

of ozone exposure and moisture did differ significantly. It 

appears, therefore, that ozone levels were uniformly high 

enough that they lacked explanatory power and, on average, 

biosites with injury had a moisture balance rather than a 

moisture deficit. One area of further research is to examine 

the relationship between injury severity on biosites and 

ozone exposure metrics under moisture balance conditions.

FIA conducts the only annual nationwide systematic 

survey for ozone-induced foliar injury. This information is 

particularly valuable to researchers studying trends in ozone 

exposure and injury, as well as to those assessing ozone 

impacts to vegetation across the United States. It is also a 

useful resource for government agencies, land managers, 

and the public as we attempt to address air quality issues 

that impact the natural resources of the Nation. 

Acknowledgments

Of vital importance to the ozone biomonitoring program 

are the forest agencies for the Southern States, the State 

coordinators, regional trainers, field crews, and quality 

assurance staff who collect and verify the ozone data. The 

ozone biomonitoring program would not be possible without 

their commitment to the collection of quality data. The 

authors would also like to thank Stan Zarnoch, Gretchen 

Smith, Sally Campbell, and Sarah Jovan for their helpful 

comments on an earlier draft of this publication.
24

General Technical Report SRS–118

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Ozone Injury Across the Southern United States, 2002–06

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Rose, Anita K.; Coulston, John W. 2009. Ozone injury across the Southern United 

States, 2002–06. Gen. Tech. Rep. SRS–118. Asheville, NC: U.S. Department of 

Agriculture Forest Service, Southern Research Station. 25 p.

In the Eastern United States, hourly concentrations of ozone typically range from 30 to 50 parts per billion 

(ppb), with events that may exceed 100 ppb. Typical exposure levels can cause visible foliar injury to 

some plant species and have the potential to reduce tree growth by up to 10 percent per year, depending 

on species and environment. As part of the Forest Service, U.S. Department of Agriculture, Forest 

Inventory and Analysis (FIA) Program, ozone-induced foliar injury is evaluated in the South between 

late July and mid-August on about 350 ozone biosites. For 2002 through 2006, ozone injury occurred 

on between 8 (2006) and 29 percent (2003) of the sampled biosites. South Carolina had the highest 

percentage of biosites with injury in 3 out of 5 years. The area at greatest risk from ozone injury occurred 

in northern Georgia. Both the moisture index and the combination of ozone exposure and moisture were 

significantly different for biosites where injury was observed and biosites where injury was not observed. 

This evidence suggests that, despite reported declines in ambient ozone concentrations over the past 10 

years, some forest areas in the South were classified in the low and no risk categories due to the moisture 

deficit conditions that existed during the 2002-06 time period. The correlation between ozone injury and 

moisture conditions, as well as the consistent low to moderate levels of injury, occurring year after year 

in some parts of the South, warrant continued monitoring and close scrutiny for potential forest health 

impacts. FIA conducts the only annual nationwide systematic survey for ozone-induced foliar injury. This 

information is extremely valuable to research on trends in ozone exposure and injury and the impacts to 

vegetation across the United States. 

Keywords: Biomonitoring, FIA, forest health, indicator species, ozone.
The Forest Service, United States Department of 

Agriculture (USDA), is dedicated to the principle of 

multiple use management of the Nation’s forest 

resources for sustained yields of wood, water, forage, 

wildlife, and recreation. Through forestry research, cooperation 

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National Forests and National Grasslands, it strives—as directed 

by Congress—to provide increasingly greater service to a growing 

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