Vegetation survey and mapping of Lake Doberdò: an analysis for the assessment of habitat conservation status of a disappearing lake of the Classical Karst (North East Italy)

Lake Doberdò is a well-known example of karst lakes, temporary lakes that seasonally fill and empty through springs and swallow holes connected to the underground waters. It is one of the few karst lakes in Italy and one of the most important examples of karst hydrology at the international level. It is an area of exceptional interest for geological-geomorphological and biodiversity conservation, and it is part the Regional Nature Reserve of Doberdò and Pietrarossa Lakes and of the Natura 2000 network. Its peculiar hydro-ecological nature allows an impressive variety of species and habitats also of high conservation value, thanks to its strong ecotonal character. However, plant biodiversity and habitats are currently threatened by several factors: a reduction of the water level, the abandonment of management of the water body, the spread of invasive alien plant species. A research project focused on the vegetation of the karst lake was recently started to provide updated basic knowledge essential for the assessment of the conservation status of its habitats, their monitoring and the planning of conservation strategies to be undertaken also in response to the rising problem of climate change that is threatening wetlands at the global level. The research was based on the following main objectives: a) vegetation analysis based on the phytosociological approach to identify plant communities and Annex I habitat types; b) vegetation mapping of plant communities and habitats, using high resolution drone orthoimagery as a baseline and fieldwork; c) a temporal comparison of the vegetation of the area after 50 years, based on a vegetation survey carried out in the 1960s; d) the identification of the most frequent alien species and the most affected habitats. In the area liable to seasonal high water (ca. 47 ha) 43 phytocoenoses were found, and 21 communities are attributed to 8 Annex I Habitats of the 92/43/EEC Directive. The particular hydrological features, the resulting ecotonal nature and the high value for biodiversity of the disappearing lake mirror the fundamental essence of habitat 3180* modelled on Irish turloughs, allowing to refer Lake Doberdò to this priority habitat type. Compared to the past, various communities show a clear change in their distribution while some valuable coenoses were not found. The vegetation survey confirms the high value of Lake Doberdò for biodiversity conservation but highlights an ongoing process of environmental change due to both natural and human-related causes including modifications of the hydrological regime and abandonment of traditional farm practices and claims the need for active conservation interventions for the preservation and the recovery of such a precious natural area.