Cost‐effective assessment of conservation status of fens

Questions How can conservation status of rich fen and alkaline spring areas be assessed most cost-effectively based on existing monitoring data? What is the precision and accuracy of available indicators? Location Rich fen and alkaline spring areas in Denmark. Methods Potential indicators of conservation status were evaluated based on: accuracy, measured as the ability to predict the number of typical species in monitoring plots; precision, measured as variation over years of indicators in repeated plots; and cost of obtaining data for the indicator. Indicators were derived using data from the Danish National Monitoring and Assessment Programme for the Aquatic and Terrestrial Environment from 2000 to 2009. Indicators included biotic indices derived from species lists, abiotic measurements of pH and nutrients and structural measurements of vegetation height and tree cover. Results The majority of indicators showed a significant correlation with the number of typical species. Floristic indicators, especially based on Ellenberg nutrient values, showed superior correlation and were furthermore very stable over years. Structural indicators were generally accurate, but were highly imprecise with high between-year variation. Among the abiotic indicators, pH and soil P were inaccurate, whereas tissue N content and nitrate in water were accurate but with low precision. When balancing efficiency of indicators with monitoring costs, laboratory analyses stand out as expensive compared to recording of a species list, the latter providing up to five valuable indicators. Conclusions Floristic indicators derived from Ellenberg values, and especially those related to nutrient availability, are cost-effective indicators of conservation status. The method is applicable to all regions where Ellenberg indicator values have been calibrated to fit local conditions.