Complementarity between the CSR and plant economic space frameworks reveals selection of marsh plant community strategies in the Seine estuary

Estuarine marsh vegetation communities are subjected to steep abiotic gradients, shaping landscape and community composition through erosion and accretion dynamics, hydroperiod and salinity. In the context of climate change, these gradients are prone to change, with potential consequences on vegetation community structure. We investigated plant traits and strategies in the oligohaline marshes of the highly anthropized Seine estuary. Infrastructures such as dykes and roads modify the local hydrodynamics through tidal restriction, thus changing the abiotic gradients. Across three sites with contrasting hydro-physico-chemical properties, we surveyed the vegetation communities along three topographical levels. Functional trait data from the TRY and GRooT databases were applied to the vegetation surveys using community-weighted means. Functional traits were linked to strategies of oligohaline marsh-communities, and have confirmed the elevation gradient to be the most contributory variable to community structure. Across the study sites, the community composition of the high marshes converged, while the low marsh communities of one restricted site diverged due to freshwater retention. Community-level functional traits merged into two major axes of the plant economic space (PES), corresponding to resource conservation and resource acquisition. The deduced life strategies of plant communities within Grime's CSR framework allowed us to quantify stress and disturbance of each site: elevation was a good indicator of stress tolerance, while higher tolerance to disturbance was mostly associated with grazing. Tidal restriction was responsible for stretched stress- and disturbance-gradients, effectively expanding the area occupied by these ecosystems while the maximum stress- and disturbance levels were similar with or without tidal restriction. • Elevation gradient shapes estuarine marsh plant communities. • Tidal restriction alters abiotic gradients, affecting vegetation. • Correspondence between CSR life strategies and PES acquisition/conservation. • Grazing linked to higher disturbance tolerance in vegetation. • Stress and disturbance gradients were stretched by tidal restriction.