The Ellenberg approach: a simple and robust alternative to the regulatory approach for delimiting wetlands in mainland France

Abstract

Wetland delineation is crucial for the protection of these ecosystems. The regulatory approach described in the legal circular of January 18, 2010 on the delineation of wetlands is not always precise, and phytosociological expertise is required for its implementation. The approach based on the Ellenberg index, which directly characterizes the soil moisture degree from the floristic composition, has so far only been used at a local scale. This study aims to evaluate the interest of using the Ellenberg moisture index for wetland delineation over all biogeographic regions and major habitat types present in metropolitan France. For this purpose, 76,284 phytosociological surveys stored in several databases were used. The moisture degree of each relevé was first determined according to the regulatory approach and then by using the Ellenberg index. The results show a strong correlation between the two approaches (from 90.6 to 96.3% according to biogeographic regions, and from 82.4 to 99.2% according to habitat types) for an Ellenberg value of 5.7 ± 0.2. They confirm that the Ellenberg moisture index approach is a simple and robust alternative to the regulatory approach for delineating wetlands.