Abstract
Coastal sandy ecosystems are increasingly being threatened by human pressure, causing loss of biodiversity, habitat degradation and landscape modifications. However, there are still very few detailed studies focussing on compositional changes in coastal dune plant communities over time. In this work, we investigated how coastal dune European Union (EU) habitats (from pioneer annual beach communities to Mediterranean scrubs on the landward fixed dunes) have changed during the last 20 years. Using phytosociological relevés conducted in 1989-90 and in 2010-12, we investigated changes in floristic composition over time. We then compared plant cover and the proportion of ruderal, alien and habitat diagnostic species ('focal species') in the two periods. Finally, we used Ellenberg indicator values to define the 'preferences' of the plant species for temperature and moisture. We found that only fore dune habitats showed significant differences in species cover between the two time periods, with higher plant cover in the more recent relevés and a significant increase in thermophilic species. Although previous studies have demonstrated consistent habitat loss in this area, we observed that all coastal dune plant communities remain well represented, after a 20-year period. However, fore dunes have been experiencing significant compositional changes. Although we cannot confirm whether the observed changes are strictly related to climatic changes, to human pressure or to both, we hypothesize that a moderate increment in average yearly temperature may have promoted the increase in plant cover and the spread of thermophilic species. Thus, even though human activities are major driving forces of change in coastal dune vegetation, at the community scale climatic factors may also play important roles. Our study draws on re-visitation studies which appear to constitute a powerful tool for the assessment of the conservation status of EU habitats.
Highlights
Coastal sandy ecosystems are currently among the most threatened ecosystems (EEA 2008)
We found that only fore dune habitats showed significant differences in species cover between the two time periods, with higher plant cover in the more recent releves and a significant increase in thermophilic species
We cannot confirm whether the observed changes are strictly related to climatic changes, to human pressure or to both, we hypothesize that a moderate increment in average yearly temperature may have promoted the increase in plant cover and the spread of thermophilic species
Summary
Coastal sandy ecosystems are currently among the most threatened ecosystems (EEA 2008). Malavasi et al (2013) evaluated changes in coastal dune spatial patterns over the last 50 years using land cover maps derived from a multi-temporal sequence of remotely sensed data These authors emphasized that the composition and structure of coastal landscapes have been drastically modified by human activities. Europe has a long tradition of vegetation surveys based on the classical phytosociological approach (Braun-Blanquet 1964; Westhoff and van der Maarel 1973; Dierschke 1994; Dengler et al 2008) This has proved a very useful methodological framework, for local and regional overviews of vegetation types (Schaminee et al 2009), and for thorough analyses of vegetation changes over time We assumed that Ellenberg indicator values, when derived from the mean values of several species in conjunction, provide reliable and calculated proxies for environmental factors when actual empirical measurements are missing (Lawesson et al 2003)
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