Undergrowth as a biomonitor for deposition of nitrogen and acidity in pine forest

The possible use of the understorey vegetation as a biomonitor for atmospheric deposition of acid and nutrients was explored by analyzing the vegetation of two pine forest stands in central and northern Sweden. Percentage cover of vascular plants, bryophytes and lichens was estimated in four factorial experiments with a total of 122 plots. In these experiments N, P, K, lime and sulphuric acid had been regularly added over a period of ca. 15 years. Redundancy analysis (RDA) was used to detect treatment effects on the composition of the vegetation, and was compared to analysis of variance (ANOVA) on Ellenberg's indicator values. Of all treatments nitrogen addition had by far the strongest effect, causing a shift in dominance from cryptogams and Ericaceae towards Deschampsia flexuosa and ruderal species. Acidification caused a decrease in the cover of most species, while liming increased the dominance of Ericaceae. There was a fairly good correspondence among the N fertilization, acidification and liming treatments and the indicator scores for nitrogen and acidity. Although the indicator method was not as sensitive as RDA in discriminating between the treatments, it may have a wider applicability in biomonitoring because it yields information on possible causal factors behind differences in vegetation.