Enough is enough: searching for the optimal sample size to characterize and monitoring sand dune Natura 2000 habitats.

In this study, we aimed at: 1) using the pseudomultivariate dissimilarity-based standard error (MultSE) to determine the adequate number of replicates needed to characterize the species composition of sand dune habitats(in coastal Tuscany) within a given precision level; 2) understanding how the observed compositional variation is partitioned among the spatial levels of the sampling design adopted. The study of the MultiSE profiles revealed that an approximate number of 10 plots was able to grasp the overall variation in plant composition for shifting coastal dunes and coastal dune scrub, while about 25 plots was needed for coastal stable dune grasslands.