USE AND IMPROVEMENT OF ELLENBERG'S INDICATOR VALUES IN DECIDUOUS FORESTS OF THE BOREO-NEMORAL ZONE IN SWEDEN

Ellenberg's indicator values for light, moisture and reaction were tested in deciduous hardwood forests of the Boreo-nemoral zone in Sweden. Weighted averages of indicator values were calculated and correlated with field measurements for two test sets of releves. The best, highly significant correlations were found for reaction, particularly for weighted averages based on vascular plant species. Significant correlations were also found for light, whereas those for moisture were less good and only partly significant. Weighted averages based on presence/absence values and those based on cover/abundance values were generally very similar to each other, but showed differences in their correlations with actual measurements. A training set of releves was used to calculate optima and ecological amplitudes of the most common species. Under certain conditions, the original indicator values were replaced by these optima in order to obtain improved indicator values for Swedish deciduous forests. These were correlated with the same test sets of field measurements as the original values and clearly gave better results for light as well as for reaction regarding vascular plants. No clear differences were found for moisture and reaction regarding bryophytes. For the majority of species, the original indicator values also expressed the ecological optima in Swedish deciduous forests as determined by this study. However, several species, most of them preferring more open habitats, showed ecological optima and amplitudes that considerably deviated from central European conditions. In conclusion, Ellenberg's indicator values can successfully be used in south Swedish deciduous forests, particularly after calibration of the values according to regional deviations.