Growth of field-grown ash trees (Fraxinus excelsior) exposed to ozone episodes

Ash trees were exposed to ozone episodes (150 nl 1(-1), 8 h d(-1), 24-27 d y(-1)) from May to October, 1992 to 1994, in open-top chambers designed to minimise microclimatic modification. Many aspects of growth were studied, including leaf abscission, leaf area, mean leaf size, tree height and girth, extension growth, cross-sectional area of annual rings and above-ground dry weight. An overview of the results is presented. This shows that the duration of the leaf fail period was increased by exposure to ozone. However, three seasons of severe ozone exposure relative to UK conditions did not significantly alter other aspects of growth.