Résumé
The Garâa Sejenane is an ancient lake in northern Tunisia that currently houses a mosaic of temporary wetlands. Comparison of modern pollen data and field vegetation surveys shows both a weak regional pollen signal and the homogenization of pollen assemblages at the scale of the garâa. Despite a hiatus between 19,000 and 2230 cal. BP, fossil pollen analyses provide the first Tunisian LGM record and attest to the ancient origin of the lake, which housed some taxa still present locally in the 1950s. The originality of the Pleniglacial surrounding landscape dominated by a juniper steppe contrasted with the mountain conifer forests in Kroumiria. Lastly, analyses of aerial photographs (1948, 1962, 1984), recent satellite photographs and previous botanical descriptions reveal that the lake has been drying since 1960 because of important anthropogenic activities (drainage, groundwater pumping, cultivation, grazing…). These disturbances have generated profound changes in hydrophytic plant communities (fragmentation, diversity loss, introduction of invasive species…) that are likely to threaten their long-term survival.