Changes in dune vegetation trends in the southeastern coast of the Iberian Peninsula

Coastal dune systems, and its vegetation, serve as a natural buffer against erosion and flooding caused by wave storms and rising sea levels. However, these systems are normally under strong pressures mainly caused by changes in land uses (e.g. tourism or urban development) which in turns could led to a perturbation of the vegetation coverage or the total replacement by hard structures such as promenades. In other coastal areas, however, the vegetation has been proved to undergo an increase in extension and coverage. This effect, known as "greening" (e.g. Jackson et al., 2019), seems to be caused by the combination of changes in climate and atmospheric composition and a reduction in windiness, among others factors. Further, the strong conservation measures carried out in these coastal areas, such as the use of fences and the restoration with autochthonous species, have contributed to this process.

This contribution focuses on testing the temporal and spatial change in dune vegetation, coverage and density, in the southeastern Mediterranean coast of Andalusia (Spain). The study site, known as Cabopino (Marbella, Málaga), presents one of the best-preserved Mediterranean coastal dunes (Artola dunes). The coastal-dune system, protected as a Red Natura 2000 site, has undergone little anthropogenic pressures in the past few years. Methodology approach includes a temporal analysis from 2017 to 2022 by calculating NDVI and EVI2 vegetation indexes using the Sentinel-2 MSI (MultiSpectral Instrument) level 2 sensor and Google Earth Engine platform. The dune area was delineated using photointerpretation techniques on the basis of the PNOA orthoimage of 2016 and considering land uses coverage maps and the European Union Habitats - EUR28 (Habitats Directive) of the same year. The NDVI and EVI2 indexes were calculated on composites of images by season (spring, summer, autumn, and winter), using the maximum values of each pixel.

Results show that vegetation coverage of the Artola dunes have remained stable during the study period (2017-2022), with small variations in the foredune sector. In terms of vegetation density, NDVI and EVI2 indexes show values of around 0.5-0.6 at the peak of vegetation development (spring and winter) which remains constant from 2017 to 2021. On the contrary, an important decrease in vegetation density is found during the 2022 spring season, with NDVI/EVI2 values of 0.1-0.25. This decrease is coincident with a negative anomaly in winter precipitation in this Mediterranean coastal area.

These preliminary results seem to be in line with previous work in the field that support the idea of a global “greening” of coastal dunes because of global (and climatic) change. Nevertheless, vegetation dynamics in Mediterranean coastal dunes seem to be highly controlled by local meteorological conditions, specially to winter precipitation, which ultimate determines vegetation growth and stabilisation.