Vegetation Patch-Level Characteristics as key Drivers of Coastal Dune Elevation: Optimizing Nature-Based Coastal Defences

<title>Abstract</title> Coastal dune vegetation is increasingly recognised as a nature-based solution for buffering shoreline dynamics, particularly by reducing the risk of inland inundation during storms. This protective function depends on the capacity of vegetated dunes to maintain or build elevation. To identify the ecological attributes influencing sediment elevation, we examined how patch size, canopy structure, dominant species identity, species composition, and plant traits shape elevation patterns across multiple coastal sites with similar dune plant assemblages. We used centimetric-precision differential GPS to measure sediment elevation inside and immediately outside vegetated patches. To our knowledge, this is the first field-based, multi-site study to directly test the effect of vegetation patch size on sediment elevation in coastal dune systems. While patch size is assumed to influence sediment dynamics, previous work has either focused on mesocosms or treated vegetation as a homogeneous cover layer, without explicitly addressing patch-scale heterogeneity. Our results show that patch size, species composition, and dominant species identity significantly influence dune elevation. Larger and mixed-species patches promoted higher sediment elevation than monospecific ones, and patches dominated by <italic>Ammophila arenaria</italic> were particularly effective. No single plant trait consistently explained elevation patterns, but our findings suggest that combinations of traits– likely related to root architecture– may enhance sediment accumulation. These results highlight key ecological attributes that support elevation gain in coastal dunes and offer insights for conservation and restoration strategies aimed at enhancing natural defences against storm-driven inundation in dynamic shoreline environments.