Calibrating ecological indicator values and niche width for a Mediterranean flora

Abstract

Bioindication of ecological variables such as humidity, temperature or pH by ecological indicator values of plants is a powerful tool for research in plant ecology, e.g. to detect early vegetation changes. Here, we provide a data set of ecological indicator values including niche width for an entire regional flora. We used an extensive data-base with floristic relevés from Southern France to recalibrate indicator values for light (L), temperature (T), continentality (K), air humidity (A), soil moisture (F), pH (R), productivity (N), soil texture (G), soil organic matter content (O) and salinity (S). Values were recalibrated using average values from co-occurring plants, enabling to develop indicator values for species not yet evaluated previously. Recalibrated values are on a continuous scale and we add standard deviation, median, first and third quartile for each indicator value. Linear regression of average indicator values against measured factors showed higher correlation with recalibrated values compared to original indicator values for temperature, pH and nitrogen, and comparable R² for moisture. Individual indicator systems performed better than a combination and applying different weighting procedures demonstrated the usefulness of inverse variance. We further illustrate graphically how recalibrated values and niche width increase ecological knowledge on plants.

Keywords:

• Bioindication
• Ellenberg
• ecological gradients
• ecological indicator values
• niche width

Acknowledgements

We thank the Conservatoire Botanique National Mediterranéen de Porquerolles and regional environmental agencies of the regions SUD-PACA and Occitanie for providing the database we used in this study. We thank Frederic Henry for sharing data on soil chemistry and vegetation relevés and Daniel Pavon for help in nomenclatural problems.

Authors’ contributions

AS conceived research idea; AS, NF and VN curated data; AS, NF and EM performed statistical analyses; AS, EM, VN, OA, VN and TD, wrote the paper; all authors discussed the results and commented on the manuscript. We thank Daniel Pavon for help with fieldwork, taxonomy and providing pictures in Figure 2.

Disclosure statement

No potential conflict of interest was reported by the authors.

Data availability statement

Floristic occurrence data are available through the SILENE database (http://flore.silene.eu, version 9/12/2021).