Cladium mariscus Phenotypes are driven by Management but Influence Vegetation Dynamics in Northern France Alkaline Fens

Large peatland areas throughout the world have been degraded, contributed to climate change, biodiversity crisis and ecosystem services no longer provided. Their restoration and long-term conservation remain challenging due to anthropogenic pressures and environmental variability. This study investigates the phenotypic plasticity and vegetation dynamics of C. mariscus populations across four restored alkaline fens in Northern France. Field surveys conducted in 2021 and 2024 assessed morphological traits, species composition, and environmental variables such as moisture and trophic conditions. The results reveal two distinct phenotypic strategies: a competitive strategy characterized by dense vegetation, thick litter layers, and low flowering rates in mature stands, and a colonizer strategy marked by higher flowering rates and lower density in disturbed or younger sites. Vegetation surveys further highlight how water level fluctuations, nutrient availability, and management practices influence community composition and habitat conservation status. These findings underscore the importance of adaptive management strategies that balance biodiversity conservation with the ecological requirements of C. mariscus populations. The study contributes to a broader understanding of phenotypic plasticity in a dominant wetland species and provides actionable insights for the restoration and management of alkaline fens in the context of climate change and eutrophication.