Species indicator values as an important tool in applied plant ecology

DIEKMANN M.

Vegetation Ecology and Conservation Biology, Dept. of Ecology and Evolutionary Biology, FB 2, University Bremen, Leobener Str., D-28359 Bremen
E-mail: mdiekman@uni-bremen.de

Plant species indicator values, especially those defined by Ellenberg, have been used widely in applied vegetation ecology, forestry and agriculture. In spite of being criticised by many researchers, there is a growing interest in using them also outside Central Europe in order to characterise communities and to analyse trends of change in the vegetation and their underlying environmental variables. The majority of species show response curves along environmental gradients that allow us to use them as bio-indicators. The most important applications of indicator values are shortly reviewed, especially the advantages – but also the problems and pitfalls – of using weighted site averages; forest data sets from South Sweden serve to illustrate some of these applications. Knowledge of the exact relationship between weighted site averages and measurements is crucial for translating the floristic data into environmental information. The calibration of indicator values to new regions can be based on indidental observations of the ecological behaviour of single species, large vegetation data sets or the simultaneous use of vegetation data sets and environmental measurements. Calibrations made for several regions support the overall reliability of indicator values, but also the necessity of adjustments when using them outside Central Europe. Provided that the limitations of indicator values are recognised, these are very useful and can complement or replace measurements to determine the values of environmental variables and to monitor their change.