What is happening to Mediterranean coastal dunes?

Prepared by Marta Gaia Sperandii

A relatively well-conserved Mediterranean dune system close to Montalto di Castro (Viterbo). Photo credit: Marta Gaia Sperandii.

This Linking to elsewhere post is related to the article “Getting the measure of the biodiversity crisis in Mediterranean coastal habitats”, published by Marta G. Sperandii and colleagues in the Journal of Ecology (https://doi.org/10.1111/1365-2745.13547), which was also advertised in the news service published by European Commission “Science and Environmental Policy“.

Coastal dunes are among the most peculiar ecosystems on Earth. They are home to a unique, highly specialised flora, and provide valuable habitats to a rich fauna. Moreover, they deliver essential ecosystem services, invaluable to our society (coastal defence, groundwater storage, climate mitigation, to name just a few of them). This is mostly due to coastal dune vegetation, particularly to a few psammophilous species which, by trapping superficial sand blown by the wind, can build and maintain sand dune systems extending up to kilometres perpendicular to the coastline.

However, in spite of their naturalistic value and of the fundamental services they provide, coastal dunes are endangered almost everywhere on the globe. Increasing urbanisation, mass tourism and related anthropogenic activities, but also coastal erosion, sea-level rise and the predicted increase in extreme climate events are among the most critical processes and factors contributing to the degradation of these fragile ecosystems. The fate of coastal dunes is particularly uncertain in the Mediterranean, where many habitats were recently classified as “threatened” by the European Red List of Habitats, and where the consequences of sea-level rise and extreme events are predicted to be especially severe.

A coastal stretch subject to high erosion (south of Termoli, Campobasso). Photo credit: Marta Gaia Sperandii.

In this context, monitoring the vegetation of coastal dunes over time is key to their conservation. Assessing shifts in the composition of coastal dune vegetation can provide us with fundamental insights into the functioning of these ecosystems, and give us an idea of whether they will be able to keep delivering the above-mentioned ecosystem services in the near future.

Between 2017 and 2018, we performed a resurveying study focused on ca. 75 kilometres of Mediterranean dune systems located in Central Italy. Specifically, we resurveyed 334 plots, originally surveyed between 2002 and 2007 and belonging to herbaceous communities of the Mediterranean coastal zonation (i.e. from drift line communities up to dune grasslands).

Resurveying coastal dune vegetation close to Tor San Lorenzo (Rome). Photo credit: Marta Gaia Sperandii.

Our goals were to (i) quantify 10-15 years changes in taxonomic and functional diversity, (ii) assess to which extent these changes derived from random fluctuations, and (iii) track shifts in individual focal species. The results of our analyses were alarming: we detected a widespread habitat loss (almost 25% of the plots unvegetated or submerged by the sea at the time of the resurvey) and found the species composition of most habitats considerably changed, especially in the upper beach, embryonic and mobile dunes. It turned out that most of these changes were “extraordinary” (i.e. they exceeded expectations under a null model), and they were driven by species loss. We could also ascertain large shifts in the functional composition of the communities, with a tendency to a decrease in plant height and an increase in the mean specific leaf area of the communities. Observed changes in single species were no less remarkable: Ammophila arenaria (the most important dune-building species, characterising the mobile dune habitat) went lost in 80% of the plots in which it was initially present.

Due to extreme coastal erosion, at the time of the resurvey several plots were found to be submerged by the sea. South of Termoli (Campobasso). Photo credit: Marta Gaia Sperandii.

The loss of Ammophila arenaria is particularly worrying: because well-conserved mobile dunes not only provide shelter for more inland communities but also guarantee high-valued services such as coastal protection, their degradation is likely to have cascading effects on the entire dune ecosystem.

By analysing different diversity facets and focusing on multiple levels of biological organisation (community and species), we managed to gain a detailed picture and highlight those habitats (upper beach and shifting dunes) that experienced the most dramatic transformations, thus offering insights for directing conservation and management efforts in Mediterranean coastal dunes.

Ammophila arenaria dominating the coastal dune landscape south of Termoli (Campobasso). Photo: Marta Gaia Sperandii.

Our work, published by the Journal of Ecology, caught the attention of a Project Editor of “Science and Environmental Policy”, a news service published by the European Commission – DG Environment and addressed to over 19,500 policymakers, academics and business-people. An article, based on our paper, has been included in one of the last issues and is available here. We think that this is a nice example of how vegetation science can (and should) reach policy and conservation managers.