Critical levels for ozone of three species of forest tree as judged by the Liphook Forest Fumigation Experiment [abstract]

Attempts arc in progress within the United Nations Economic Commission for Europe to define "critical levels" for various receptors. The critical level is intended to be the concentration of a pollutant at which there is no significant harmful effect. Setting a critical level for ozone effects on forest trees is handicapped by a shortage of experimental data under European conditions. During the Liphook Forest Fumigation Experiment, three species of forest tree (Scots pine, Norway spruce and Sitka spruce) were fwnigated with 03 at a target concentration of I .5x ambient for 3.5 years in an open-air fumigation system. Ozone effects were not large, suggesting that the critical level should be correspondingly high. The open-air technique gives data free from chamber artifacts, but may introduce artifacts of its own. This paper will briefly review the effects 3 had on the trees; consider different measures of 03 exposure an whether the experimental conditions gave a proper concentration-frequency profile; factors (soil, climatic etc.) which could have modified the response; and finally the implications for critical levels.