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Recommendations for improving the scientific understanding of ozone impacts on vegetation have been summarized in sections 8.4 and 14.2.7 of the Science Assessment Document. Most limiting is the dearth of information on experimental exposures of Canadian agricultural and forest species, grown under Canadian field conditions, at realistic (i.e. near ambient) ozone levels. The analyses in this assessment are to a large extent based upon experimental data collected in the United States and Europe. While the theoretical understanding of ozone vegetation impacts and ambient characteristics of ozone in Canada support the use of this information, it is important that experimental work be carried out to assess exposure - response relationships for Canadian crops and forest species under Canadian climatic and pollutant conditions. In the meantime, it is recommended that when species specific response information is required, the individual LOAELs, presented in Tables 1 and 2 (SAD Tables 8.9 and 8.11) for agricultural crops and forest species respectively, be used. For a conservative estimate of the concentration of ozone above which effects on vegetation can be expected, the LOAEL ranges of 5900-7400 ppb-h (crops) and 4,400-6,600 ppb-h (trees) (3 month SUM60 values) identified in Section 6.2 above should be used.
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