Relationships between crown condition of beech (Fagus sylvatica) and throughfall chemistry

A two-step regression procedure was used to predict the impact of throughfall chemistry on the defoliation of Fagus sylvatica L. over a 10-year-monitoring period at three plots in northern Belgium. The impact of throughfall chemistry on crown condition was examined after accounting for influences of site, stand, climate and diseases. In a first step, defoliation was regressed on site, stand, climate and disease parameters. The residual defoliation of this standard set was correlated with 27 throughfall variables.
Climatic variables of the year preceding the year of crown assessment accounted for 79% of the variation in current defoliation. Site, stand and disease factors were not included and were still part of the residual defoliation. The study of the residual defoliation revealed that high throughfall depositions of sulphate and ammonium and high throughfall ratios of SO₄/Mg enhanced defoliation.