| Knowledge needs: The use of expert-based indicator values (Ellenberg) to estimate abiotic conditions from vegetation is widespread. However, recent research has shown that expert judgement may contain considerable bias and thereby introduces a large amount of uncertainty. Could expert based indicator values be replaced by indicator values based on field measurements? Research objectives: Research objectives include: 1. Development of an approach to fill gaps in existing knowledge as efficient as possible; 2. Collecting abiotic and vegetation data, following the method and selected locations as under 1. 3. Completing, clearing and maintaining the existing `KENNET2¿- database; 4. Interpreting of collected data by a) deriving an optimal method to characterize the response for each species, b) researching the importance and developing a method to characterize interactions, c) researching the estimation of the responses of species with insufficient available data, d) providing the responses at different platforms for the public. Results and products: We were able to estimate the pH response of 556 species of the Dutch flora. Ca. 20% of the responses were, at least, bimodal and many responses had a very wide range. The simplest method (`raw mean¿) yielded the best prediction of pH; the indicator value of a species is the mean of the soil pH values of the sites where it was observed. A list of all ¿raw mean¿ estimates per species is given. The predicted pH of a new site is the mean of the indicator values of the present species. The estimated species responses were validated on independent Dutch and European data sets. Older successional stages were predicted better than younger stages. Our method performed better than the popular Ellenberg indicator system for the Dutch data set, while being just as easy to use, because it only needs a single value per species. We foresee that, when more data become available, our method has the potential to replace the Ellenberg system. Major products are: - Presentation: Wieger Wamelink, Paul Goedhart, Han van Dobben & Frank Berendse: The Response Of Plant Species To Soil pH: Replacing Expert Judgement By Measured Responses; - CD: `Plant species response for abiotic soil variables; response curves and optima¿; - Article: Wamelink, G.W.W., Goedhart, P.W., Dobben, H.F. van & Berendse, F. 2005. Plant species as predictors of soil pH: Replacing expert judgement with measurements. Journal of Vegetation Science 16: 461-470. |