When dynamism is the baseline: long-term ecology of a Mediterranean seasonal wetland in the Donana National Park (Southwestern Europe)

Mediterranean seasonal wetlands are amongst the world's most endangered ecosystems. Although seasonal wetlands' conservation is a European continental-scale priority, their long-term ecological dynamics are not well known, hampering the detection of baseline conditions. However, a long-term ecological viewpoint could aid in the detection of spatiotemporal factors controlling wetland development. We have applied a multi-proxy palaeoecological approach (palynological, microcharcoal, magnetic susceptibility, loss on ignition and diversity estimates analyses) on a 360-cm core retrieved from the El Sopeton (ElSo), a temporary wetland nested between dunes in the paradigmatic Donana coastal area. The palaeoecological analyses reveal300-500-year-long wetland phases linked to dune immobilisation during humid periods. During the first wetland phase (AD40-315), upland and wetland vegetation diversity dynamics follow opposite trends owing to the different effect that dune proliferation had on them. Fixed dune landscapes provided upland spatial diversification, while they promoted a longer hydro-period in ElSo, simplifying wetland vegetation. During the second wetland phase (AD1550-2012), land-use change drove environmental dynamics. The mid-eighteenth-century pine afforestation to fix moving dunes marked an environmental tipping point, with the ElSo wetland transitioning from seasonal to permanent. This translated into a rising trend in upland diversity and a decreasing trend in the wetland one. Despite the recent pine afforestation, the palaeoecological findings evidence the autochthonous character of Pinus pinea, as well as the naturalness of the wetland species Hydrocharis morsus-ranae and Ricciocarpos natans. The geomorphological dynamism of the diverse Donana coastal setting is the baseline for the area, modulating wetland-upland water connectivity and, ultimately, controlling biodiversity trends. The preservation of Donana natural dynamism and landscape heterogeneity should be considered for the management, conservation and restoration of its seasonal wetlands.