Growth of mature beech in relation to ozone and nitrogen deposition:: An epidemiological approach

Stem increment of mature Fagus sylvatica L. from 57 plots in Switzerland was analysed with respect to environmental factors using multilinear regression. Nitrogen (N) deposition was positively correlated with stem growth, with an increase by 41.8% (confidence interval 38.9-44.2) per 10 kg N ha(-1) a(-1). There was a negative relationship between ozone (O-3) dose and diameter increment. The fit was better for maximum rather than average exposure values. Coefficients indicated growth changes of -22.5% (14.3-28.6 confidence interval) and -35.1% (17.8-47.3) respectively per 10 ppm hours. These changes exceed the -6.1% found in experiments with beech seedlings. This difference is mainly attributed to the fact that the seedling data are calculated for a single season's exposure whereas the stem increment data extend over four years, representing the product of four annual reductions. Increased sensitivity of mature trees compared to seedlings, however, is also suggested.