Selection and use of bio-indicators to assess the possible effects of climate change in Europe

From paleoecological records it is well known that past climate changes have led to considerable changes in the species composition of ecosystems and larger spatial units such as landscapes and even continents. The observed increase in average global temperature since the beginning of this century is strong compared to previous warming periods and, if the climate models are correct, future warming will be even stronger and faster. Especially in Western Europe, where the landscape has been greatly fragmented by human activities, the ongoing and projected changes in climate will impose additional stress on the natural biodiversity which is already greatly reduced. In order to be able to detect responses of individual species to climate change, to assess 'critical levels' and to develop anticipating measures, better information on climate sensitivity of species (and ecosystems) is essential. This paper will discuss criteria and methods for the selection of bio-indicators for climate change. Examples of changes in distribution and phenology of some western European species, which are possibly related to a changing climate, are given. The preliminary results of a pilot study on the selection of indicator species for the Netherlands are presented and discussed. The paper concludes with a discussion on the need of, and possibilities for, more systematic long-term ecological research and monitoring of the effects of climate change on species and ecosystems in Europe.