Diachronic Observations Reveal Different and Scale-Dependent Response of Sand Dune Plants to Seashore Dynamics

Climate change and human infrastructures heavily affect seashore dynamics with cascading consequences on coastal sand dunes. While there is a high number of studies conducted on plant communities, there is a lack of monitoring approaches conducted at population level. We studied the variations in spatial patterns of the population of three plant species in response to interannual coastline variation in a coastal Nature Reserve. We performed eight diachronic field observations over the course of eleven years, in which we registered the coastline variation and the position of each functional individual of the selected species. The population of the alien-naturalized and highly clonal Sporobolus pumilus demonstrated the ability to follow the interannual variations of the coastline, thus maintaining a constant distance from the seashore. In contrast, the native Polygonum maritimum and the dune-builder Thinopyrum junceum showed a progressive reduction of the distance from the seashore (− 21 m and − 16 m, respectively). However, this effect was detected only at a finer spatial scale, thus revealing the scale-dependence of this phenomenon. In addition, the spatial distribution patterns of T. junceum changed with the variation and stability of the seashore, showing spatial dispersion and aggregation patterns, respectively. Our study reveals how the plant response to the coastline variation was species-specific, probably depending on species functional strategies. Besides highlighting the importance of frequent diachronic surveys, our population-level approach may help in explaining the compositional changes observed at higher organizational level. Finally, our findings indicate that coastal erosion poses a serious threat for the conservation of dune ecosystems.