3 Results Multi-species indices
3.1 All vascular plant species
The MSI based on all (modeled) vascular plant species is reported here only for completeness, but it should be noted that it is not a useful overall measure of change. Indeed, when comparing this with the more focused MSI’s for specific sets of species and with the numbers of species that had an increase or decrease (last year versus first year - as indicated on the right hand side of the figures), it is clear that the overall multi-species index averages out opposing underlying trends. Moreover, in general, if a species shows an increasing trend (or decreasing trend), we cannot tell if this is to be evaluated as a positive or a negative thing without consideration of the species traits and the environmental changes that caused the species to increase or decline. For instance, an invasive plant species may show a strong increasing (‘positive’) trend, but will be evaluated as negative because of its potential negative impact on native plant and animal communities. Similarly, a native, competitive, nitrogen-demanding plant species with an increasing (‘positive’) trend, could be a consequence of high levels of atmospheric nitrogen-deposition and thus be evaluated as negative.