Abstrakt
QuestionIs it possible to construct indicator values that would place individual species on gradients of disturbance frequency and severity? We suggest that such indicator values could be defined on the basis of the disturbance regimes under which individual species occur, to be independent of their traits. They should also separate disturbance frequency from disturbance severity.
LocationCzech Republic. MethodsWe used a stratified set of 30 115 vegetation-plot records sampled over the whole country and classified into 39 phytosociological vegetation classes.
Each class was assigned values of disturbance frequency and severity by expert judgement. A Disturbance Frequency Index for each species was calculated as the mean of the common logarithm of the disturbance frequency of all vegetation classes weighted by occurrence frequencies of this species in those classes.
A Disturbance Severity Index was defined as mean disturbance severity of all vegetation classes weighted by occurrence frequencies of this species in those classes. For forest vegetation, indices were computed separately for the whole community and for the herb layer, which experiences different types of disturbance.
Further, we constructed a disturbance index from vegetation structural parameters, viz. summed covers and community-weighted mean of height at maturity of species recorded in each plot for each vegetation class. We assessed all indices by comparing their values with data on functional traits of the species.
ResultsWe calculated values of the indices for 1248 species. The Disturbance Frequency Index and Disturbance Severity Index were correlated, but still described different responses of individual species to disturbance.
The index based on vegetation structure was correlated mainly with the Disturbance Frequency Index.