Evidence for Ozone-Induced Foliar Injury

RESEARCH DOI: 10.1007/s00267-001-0011-5 Remote Assessment of Forest Health in Southern Arizona, USA: Evidence for Ozone-Induced Foliar Injury JEREMY E. DIEM optimal change detection areas, with one site, TVWMica, ex- Department of Anthropology and Geography, posed mostly to the Tucson air pollution plume, while the Georgia State University, other site, EMica, was more protected from Tucson-derived 33 Gilmer Street, pollution. An overall increase in VI from 1972 to 1992 at both Atlanta, Georgia 30303-3083, USA sites appears to have been caused by an increase in moisture availability. Larger foliar injury values in 1985 were associated ABSTRACT / This paper examines possible ozone-induced with a smaller increase in VI (i.e., a smaller increase in green foliar injury to ponderosa pine areas in the Rincon Mountains leaf biomass) from 1972 to 1986. From 1972 to 1986 and of southern Arizona from 1972 to 1992. Spatiotemporal differ- from 1986 to 1992, VI values at TV/WMica increased at a ences in a satellite-derived vegetation index (VI) are examined slower rate compared to those at EMica. The reduced in- with respect to antecedent moisture conditions, temporal vari- crease in “green-up” may have been caused partially by ations in ozone exposure levels, and measured foliar injury ozone-induced foliar injury and resulting decreases in green values from 1985. Seasonal ozone exposure levels (SUM60 leaf biomass. However, these spatial differences in VI values and W126) increased from 1982 to 1998 and were signifi- may have also been caused by a number of other factors. Re- cantly correlated (r ϭ 0.49 and 0.53, ␣ ϭ 0.05) with annual sults nevertheless reveal the strong possibility of distinct, to- population totals in the Tucson area. Extensive masking of pographically based, spatial variations in ozone-induced foliar satellite images from 1972, 1986, and 1992 resulted in two injury within the Rincons. Coniferous forests in the “sky islands” of the south- not be located near urban areas, ozone can be trans- western United States are a valued resource, resulting ported hundreds of miles downwind from urban partially from their relatively small coverage of the re- sources and persist for hours [United States Environ- gion’s landscape. For example, coniferous forests com- mental Protection Agency (U.S. EPA) 1984]. Rural, prise just 1% of the Tucson, Arizona, region’s total area western atmospheres can have high ozone concentra- (Diem and Comrie 2000). Like other forests, sky island tions, for between 1980 and 1988, 56% of ozone mon- forests are affected by a variety of stressors that affect itoring sites in or near western forests exceeded the their overall health. Major causes of stress include nat- federal ozone standard at least once (Bo¨hm and Van- ural competition, climate, biological factors (e.g., in- detta 1990). For the most part, ozone-related tree dam- sects and fungi), chemical deficiencies or excesses, and age is caused by absorption of sublethal amounts of direct human disturbance (e.g., logging) (Cowling pollutants over a long period of time (Reich and 1989). These, however, are not the only stressors. Amundson 1985). Shorter exposure to relatively high Forests within and/or proximate to urban, indus- concentrations, such as those higher than 80 ppb, can trial, and mining areas have been found to be affected also cause injury (Bo¨hm et al. 1995). Chronic exposure by air pollution, a form of indirect human disturbance. to ambient ozone can cause substantial loss of vigor, Ozone, which is a secondary air pollutant formed by the which can in turn lead to increased susceptibility to oxidation of volatile organic compounds (VOCs) in the additional stresses (e.g., drought and insects), abnor- presence of nitrogen oxides (NOx) and sunlight (Cha- mally high tree mortality, and potential changes in meides et al. 1992), is the only regionally dispersed air forest structure and function (Miller et al. 1982). pollutant that has been rigorously proven to cause det- rimental effects on forests (Bates and Sizto 1987; Wood- Ozone and Forest Health in the Western man 1987; Cowling 1989). Even though forests might United States In the western United States, most research concerning ozone and forest health has been conducted in the KEY WORDS: Ozone; Ponderosa pine; Foliar injury; Landsat MSS; Veg- ponderosa pine (Pinus ponderosa Laws) and Jeffrey pine etation index; Southwestern United States (Pinus jeffreyi Grev. and Balf.) forests in California’s San Environmental Management Vol. 29, No. 3, pp. 373–384 © 2002 Springer-Verlag New York Inc. 374 J. E. Diem Bernardino Mountains and Sierra Nevada Mountains. Purpose and Goals Damage to those ozone-sensitive pine species is indi- The purpose of this paper is to assess the capability cated by chlorotic mottling, tip necrosis, reduced nee- of multitemporal satellite imagery for uncovering cir- dle retention, tufted crowns, reduced needle length, cumstantial evidence of ozone-induced foliar injury in reduced needle density, and reduced growth (Innes ponderosa pine areas of the Rincon Mountains of 1992). In addition to the direct impacts of ozone, trees southern Arizona. The three major goals are (1) to in an advanced state of chlorotic decline are attacked establish a link between 1985 field-based foliar injury more frequently by both the western pine beetle and values and image-based VI changes from 1972 to 1986, the mountain pine beetle than are healthy trees (Cobb (2) to establish a link between temporal variations in VI 1968). values and expected ozone exposure levels, and (3) to Smith (1981) noted that, in the San Bernardinos, an provide useful preliminary results on which future stud- average 30-year-old ponderosa pine that grew during a ies can be based. time period (1941 to 1971) with relatively high pollution levels was considerably smaller than a similar tree that grew during a low-pollution time period (1910 to Study Region 1940). Also in the San Bernardinos, from 1978 to 1988, ϳ decreases in ozone injury were linked to decreased The Rincon Mountains ( 32°N latitude and ϳ ozone concentrations (Miller et al. 1989). A similar 110°W longitude) are located east of Tucson in south- relationship between ozone and forest health was ern Arizona (Figure 1). Saguaro National Park (SNP) found in the Sierra Nevadas. Symptoms of ozone injury East contains most of the mountainous areas. The Rin- to pines have been documented within a 500-km-long cons are rugged mountains with an elevation range of ϳ ϳ area on the western side of the southern Sierra Nevadas approximately 1600 m ( 1000 to 2600 m a.s.l.) and (Warner et al. 1982). Williams et al. (1977) found an especially steep eastern face. Mica Mountain and ozone injury predominantly in the low-elevation pon- Rincon Peak are the two highest points in the Rincons. derosa pine forests on ridges that rise abruptly from the Vegetation consists generally of Sonoran desert scrub San Joaquin Valley floor. Most injury occurred at mid- (i.e., palo verde and mesquite) at lower elevations, dle elevations due to concentration of pollutants at Madrean evergreen woodland (i.e., juniper and ever- inversion boundary zones on rising mountain slopes. green oak) at middle elevations, and Madrean montane Concerning tree growth in the southern Sierra Neva- conifer forest (i.e., pine and Douglas-fir) at higher das, Jeffrey pines with symptoms of ozone injury had elevations. On the Rincons and most of the Southwest’s other “sky islands,” ponderosa pine is the most com- 11% less radial growth than pines without ozone injury; mon montane tree and often grows in pure stands sites with reduced growth faced the San Joaquin Valley (Brown and Lowe 1983). Two varieties of ponderosa (Peterson et al. 1987). pine in the Rincons are Arizona pine [P. ponderosa var. Remote Sensing of Pollution Damage arizonica (Engelm.) Shaw] and Rocky Mountain ponderosa pine [P. ponderosa var. scopulorum (Engelm.)] Satellite data have proven useful for detecting vege- (Little 1976). tation stress, including pollution-induced stress (Vo- The upper elevations of the Rincons have a warm gelmann 1988; Hagner and Rigina 1998). In areas temperate climate, with average annual temperatures where no ground truth is available, remote sensing can around 9°C(ϳ50°F) and an annual precipitation total still be used to identify where vegetation is stressed with of approximately 780 mm (ϳ31 in.) (Figure 2). Daily the aid of vegetation indices. The simple vegetation maximum temperatures reach 25°C(ϳ77°F) during index (VI), which is the ratio of near-infrared to red June and July, while daily minimum temperatures drop reflectance, is significantly correlated with the total to Ϫ4°C(ϳ25°F) in January. The Rincons have a bi- green leaf biomass (Tucker 1979). Therefore, temporal modal precipitation regime with relatively wet winters changes in VI values provide a means for deciding and summers. In winter, midlatitude storms move whether a vegetation canopy has been significantly al- through the region (Comrie 1996). During July and tered (Nelson 1983). Nevertheless, some researchers August, a monsoon-like circulation advects the bulk of have found that air pollution injury is insufficient to the moisture from the eastern tropical Pacific Ocean register as spectral changes above the background vari- and the Gulf of California (Adams and Comrie 1997). ation induced by natural variations in canopy closure Motor vehicles are the primary sources of the Tuc- and vegetative composition within the target vegetation son region’s ozone precursor pollutants (i.e., VOCs and type (Westman and Price 1988). NOx) (Diem and Comrie 2001). Tucson’s motor vehi- Remote Assessment of Forest Health 375 Figure 1. Map of the study region showing the locations of the two study areas, TVW/Mica and EMica, in the Saguaro National Park East portion of the Rincon Mountains as well as their proximity to Tucson.

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