Through the lens of time - experiences from a resurveying study of coastal dune ecosystems in Central Italy

Abstract

Located at the boundary between land and sea, coastal dunes are dynamic ecotones characterized by constraining environmental conditions, notable habitat heterogeneity and a highly specialized flora. However, in spite of their prominent ecological value and a wide range of socio-economic services provided, coastal dunes are listed among the most threatened ecosystems on earth, appearing worldwide squeezed between massive urbanization and global changes. Monitoring their status through time should be therefore considered as top priority for promoting the conservation and improving the management of these vulnerable ecosystems. By allowing the quantification of community changes and the assessment of main trends, resurveying studies proved to be effective tools to track temporal changes in a variety of natural habitats. We hereby present results from a resurveying study performed on coastal dune ecosystems of Central Italy. A set of 334 georeferenced random plots, originally sampled between 2002 and 2007 and belonging to the first portion of the coastal vegetation zonation (from upper beach communities to coastal stable dune grasslands), was resurveyed during two sampling seasons (2017-2018). To investigate community changes in composition and abundance, beta diversity metrics based on both presence/absence and abundance data were computed for each pair of old vs new plots. Each of these metrics was tested for significant differences among vegetation communities using non-parametric tests. Furthermore, changes in occurrence frequency and cover were analyzed for a set of diagnostic species in each reference community by using McNemar’s tests for paired data and Wilcoxon signed-rank tests. Results suggest how, during the investigated time-span, coastal dune communities of Central Italy experienced considerable changes affecting both species composition and dominance structure. Although all investigated communities were somehow affected, upper beach communities, embryonic and shifting dunes experienced the most important transformations, as also confirmed by the analysis of diagnostic species. Specifically, the loss in both occurrence frequency and cover of Ammophila arenaria subsp. australis appears to be particularly alarming, given the key functional role played by this perennial rhizomatous grass in the dune-building process. Overall, our results suggest that the last 10-15 years brought considerable deterioration in the conditions of coastal dunes, probably induced by the combined action of multiple natural and anthropogenic drivers, and urgently call for specific conservation efforts.