GROWTH OF FIELD-GROWN ASH TREES (FRAXINUS-EXCELSIOR) EXPOSED TO OZONEEPISODES

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 de signed to minimise microclimatic modification. Many aspects of growth were studied, including leaf abscission, leaf area, mean leaf size, tr ee height and girth, extension growth, cross-sectional area of annual rings and above-ground dry weight. An overview of the results is prese nted. This shows that the duration of the leaf fail period was increas ed by exposure to ozone. However, three seasons of severe ozone exposu re relative to UK conditions did not significantly alter other aspects of growth.