Ecobordure: a flora-based indicator to assess vegetation patterns of field margins and infer its local drivers. Design in Brittany (France)

Field margins are key landscape elements contributing to maintain biodiversity in agricultural landscapes. Yet, their ecological value is often poorly assessed and restricted to landscape descriptors, e.g. density or structure of hedgerows. We introduce Ecobordure, a flora-based indicator designed to describe vegetation patterns of field margins and infer on drivers leading to these patterns, i.e. structure and management practices of field margins. Ecobordure first targets agricultural teachers and advisers, who want to learn and help students and farmers to learn about patterns and drivers of field margin vegetation, for promoting management practices favorable to this biodiversity. Here, we present the stages of the Ecobordure design and output validation. The first stage consisted of elucidating the relationship between vegetation composition and structural and management characteristics of field margins. Canonical Correspondence Analyses were performed on empirical datasets derived from field work in bocage regions of Brittany (north-western France). This first stage led to the selection of 31 reference species, quite common, easy-to-recognize and representative of i) the whole community and ii) a wide range of ecological attributes. The 31 reference species were classified in three groups sharing similar life history traits and ecological attributes: "forest-edge", "grassland" and "weed" species. The second stage consisted of the graphical representation of field margins in a triplot diagram, the "Ecobordure triangle", according to the relative percentage of the three species groups. The representation of the Ecobordure triangle was then refined through segmentation in seven sectors to facilitate the reading and interpretation of results. Finally, the output validation of the indicator was performed by testing the consistency between Ecobordure outputs and structural and management characteristics of field margins, using an independent dataset. Our results demonstrate that Ecobordure is a simple, efficient and reliable indicator allowing users to characterize vegetation patterns of field margins and identify potential drivers leading to these patterns. In its original form, Ecobordure can be applied to a broad spectrum of field margins in European bocage regions with temperate oceanic climate, on acidic to neutral soil. However, its use can be extended to other agricultural regions through adaptation of the species list. We conclude by giving some information about Ecobordure use and appropriation by end users.