Assessment of the dynamic trajectories and maritime character of Armorican cliff-top coastal heathlands

Abstract

Atlantic coastal cliff heathlands are chamaephytic vegetation dominated by Ericaceae, most often associated to Fabaceae (Ulex) and integrated from a phytosociological point of view into alliance of Dactylido oceanicae-Ulicion maritimiGéhu 1975 (class of Calluno vulgaris-Ulicetea minoris Braun-Blanq. & Tüxen ex Klika & Hadač 1944). This alliance gathers coastal heathlands under marine influences whose physiognomy is marked by prostrate or halo-anemomorphic chamaephytes. All Atlantic heathlands are included into habitats of European community interest which justify the designation of Natura 2000 sites. Within these protected areas, heathland conservation or restoration management issues raise the question of the choice of nature and frequency of management methods. For that, it seems important to understand the dynamics of cliff-top coastal heathlands. Stable heathlands, considered as permanent vegetation of primary character, can be managed without any intervention, while heathlands characterized by a progressive dynamic may be subject to interventionist management. The aim of this work is to present the main determinant abiotic and biotic factors driving the cliff-top coastal heathlands. Human uses may influence the composition and structure of these vegetation. This approach helps to assess the primary or secondary character of cliff-top coastal heathlands vegetation, their stability or dynamic. This article clarifies the notions of primitive, primary and secondary coastal heathlands. It proposes criteria to differentiate stable heathlands and unstable heathlands which are characterized by a progressive dynamic towards coastal scrublands or forest: abiotic conditions, floristic combination, physiognomy. The synphytosociological methodology is useful for establishing the typology of the series, permaseries and minoriseries, in which the different types of cliff-top coastal heathlands are included.