Ambient ozone effects on forest trees of the eastern United States: a review

Abstract

Tropospheric ozone can affect crop yield and has been reported to cause reductions in growth and biomass of forest tree species in laboratory and glasshouse studies. However, linkages between growth and ambient ozone concentrations in the field are not well established for forest trees. Ambient ozone concentrations have been shown to cause foliar injury on a number of tree species throughout much of the eastern USA. Symptom expression is influenced by endogenous and exogenous factors and, therefore, ozone-exposure\tree-response relationships have been difficult to confirm. Clearly defined, cause-effect relationships between visible injury and growth losses due to ozone have not been validated. Generalizations of sensitivity of forest trees to ozone are complicated by tree development stage, microclimate, leaf phenology, compensatory processes, within-species variation and other interacting stresses. In general, decreases in above-ground growth at ambient ozone levels in the eastern USA appear to be in the range of 0-10 % per year. However, these conclusions are based on a small number of tree species, with the vast majority of studies involving individual tree seedlings in a non-competitive environment. Comparative studies of small and large trees indicate that seedlings are not suitable surrogates for predicting responses of mature trees to ozone. Process-level modelling is a promising methodology that has been recently utilized to assess ozone effects on a stand to regional scale, indicating that ozone is affecting forest growth in the eastern USA. The extent and magnitude of the response is variable and depends on many edaphic and climatic factors. It is imperative when conducting assessment exercises, however, that forest biologists constantly keep in mind the tremendous variability that exists within natural systems. Scaling of single site\physiological response phenomena from an individual tree to an ecosystem and\or region necessitates further research.

Responses of evergreen and deciduous Quercus species to enhanced ozone levels

“…As observed in these two species, sclerophyllous adaptations include the development of cells with thick walls and more supportive tissue that can affect gas diffusion inside the leaves. Thick leaves are considered to be more ozone-tolerant than thinner leaves (Pääkkönen et al, 1995a(Pääkkönen et al, , 1997Bennet et al, 1992;Lyons et al, 2000;Karlsson et al, 2007), in part because of differences in the gas-phase diffusion pathways (Chappelka and Samuelson, 1998). The presence of cells with thick walls strongly influences the length of the diffusion pathway for ozone and modifies the interaction with oxidative constituents of the apoplast; the density of the cell wall (i.e., degree of cross-linking, suberification or lignification) would also be expected to influence the tortuosity of the diffusion pathways for ozone (reviewed in Lyons et al, 2000).…”

New exposure-based metric approach for evaluating O3 risk to North American aspen forests

“…Since the late 1950s, an extensive scientific literature has been built on the O 3 impacts on forest trees (see reviews by Kickert and Krupa, 1990;Chappelka and Samuelson, 1998;McLaughlin and Percy, 1999;Percy, 2002;Percy et al, 2003;Andersen, 2003;Ashmore, 2004;Karnosky et al, in press), forest ecosystems (Miller and McBride, 1999;Bytnerowicz et al, 2003) and physiologically based modeling of North American forest response. Ollinger et al (1997) simulated the effects of O 3 on hardwood forest types in the northeastern US and estimated growth reductions between 3% and 22%.…”

Fingerprinting the impacts of global change on tropical forests

“…Plants grown under high O 3 levels exhibit decreased growth and visible damage (Reich & Amundson 1985;Skärby et al 1998;Chappelka & Samuelson 1998;Innes & Haron 2000). O 3 enters the stomata where it oxidizes one of several chemical compounds, which then reduces cell membrane integrity affecting their ability to transport chemical substances and maintain homeostasis.…”