"In compiling more than 55 studies, Wittig et al. (2007) reported that current O3 concentrations in the northern hemisphere are decreasing photosynthesis (-11%) and stomatal conductance (-13%) across tree species. They also found that younger trees were less affected than older trees.
"A continuing lack of information precludes offering any generalizations about interactive effects of O3 with NH3, HF, or heavy metals."
"New ecological analyses expand the already large body of evidence indicating that O3 exposure causes injury to plants."
"...the average incidence of O3-induced foliar injury was 73% on milkweed in the Great Smokey Mountain National Park in the years 1992-1996."
"...current levels [of ozone] have been shown to reduce the ability of many sensitive species and genotypes within species to adapt to or withstand other environmental stresses. These may include increased susceptibility to freezing temperatures, pest infestations and/or root disease, and compromised ability to compete for available resources."
"...the cumulative effects of ambient levels of O3 decreased seasonal stem growth by 30-50% for most trees species in a high O3 year in comparison to a low O3 year..."
"...many national parks and natural areas have monitored O3 levels above concentrations that have been shown to decrease plant growth..."
"This level of exposure has been estimated to cause a 9% biomass loss in 50% of the 49 tree seedling cases studied...1996"
"Yield loss also may include changes in crop quality, i.e., physical appearance, chemical composition, or the ability to withstand storage."
"These symptoms are considered diagnostic as they have been verified in exposure-response studies under experimental conditions. Typical visible injury symptoms on broad leaved plants include: 1) acute exposure (pigmented lesions (stippling), flecking, surface bleaching, and/or bifacial necrosis); 2) chronic exposure (pigmentation (bronzing), chlorosis or premature senescence). Typical visible injury symptoms for conifers include: 1) chlorotic banding or tipburn (acute exposure); 2) flecking or chlorotic mottling, premature senescence of needles (chronic exposure)."
"Many studies have demonstrated that root growth is more sensitive to O3 exposure than stem or leaf growth."
"...incidence of O3 induced visible foliar injury is widespread across the eastern and western U.S. Visible foliar injury was observed in counties that are meeting the current level of the 8-hr standard and an alternative secondary standard option of a SUM06 of 25 ppm-hr proposed in 1996."
"Ozone and other photochemical oxidants may influence the severity of a disease or infestation either by direct effects on the causal species, or indirectly by affecting the host, or both. Likewise, mutually beneficial relationships or symbioses involving higher plants and bacteria or fungi may also be affected by O3."
"Several new studies have been published on the incidence of foliar injury in the field due to ambient O3 concentrations."
"The oldest and clearest example involves the San Bernardino Mountain forest ecosystem. In this example, O3 appeared to be a predisposing factor leading to increased drought stress, windthrow, root diseases, and insect infestation (Takemoto et al., 2001). Increased mortality of susceptible tree species, including ponderosa and Jeffrey pine, resulting from these combined stresses has shifted community composition towards white fir and incense cedar and has altered forest stand structure (Miller et al., 1989). A shift of community composition towards white fir may make this ecosystem more susceptible to fire."
"By affecting water balance, cold hardiness, tolerance to wind and by predisposing plants to insect and disease pests, O3 may even impact the occurrence and impact of natural disturbance (e.g., fire, erosion)."
"...effects on individual keystone species and their associated microflora and fauna, which have been shown experimentally, may cascade through the ecosystem to the landscape level."
"...small effects on individual tree growth may result in substantial effects on forest stand growth after many years."
"Since it has been established that O3 affects photosynthesis and growth of plants, O3 is most likely affecting the productivity of forest ecosystems."
"...the National Academy of Sciences on Air Quality Management in the United States (NRC, 2004) stated that “EPA’s current practice for setting secondary standards for most criteria pollutants does not appear to be sufficiently protective of sensitive crops and ecosystems...”
"The epidemiologic evidence from recent publications provides further evidence that short-term exposure to O3 is associated with effects on the respiratory system, and also report associations with mortality.
Many new toxicological studies are available on respiratory or allergic effects; in addition, some have suggested systemic effects of O3 on the cardiovascular or neurological systems."
"Recent results confirm that yields and quality of multiple-year forage crops are reduced at sufficient magnitude to have nutritional and possibly economic implications to their use as ruminant animal feed at O3 exposures that occur in some years over large areas of the U.S. Ozone may also reduce the quality or nutritive value of annual species."
"Ozone can also have indirect effects on herbivorous animals due to O3-induced changes in feed quality."