Veronica oetaea, a critically endangered narrow endemic of Mt. Oeta (Central Greece): Population dynamics and conservation threats

• High altitudinal MTPs flora cycles are disturbed by increased summer rainfall. • Secondary flooding evemts in MTPs disrupt the annual reproductive cycle of V. oetaea. • Prolonged inundation periods and higher temperatures lead to changes in floristic composition. • In contrast to low-altitude MTPs, increased drought and its associated impacts are not observed at higher elevations. • Species like V. oetaea are likely to face extinction in the near future under the altered hydrological regime. Veronica oetaea Gustavsson is an annual, narrow-range endemic plant, a specialist of Mediterranean Temporary Ponds (MTPs), and a priority species under the EU Habitats Directive. Its entire global population is confined to three high-altitude MTPs (Alykaina, Greveno, and Livadies) on Mount Oeta, Greece. MTPs are a priority habitat under the Habitats Directive 92/43/EEC (code: 3170*). A twelve-year monitoring program (2013–2024), one of the few long-term MTP studies, revealed a marked population decline. The subpopulation in Livadies, the largest pond inhabited by the species, experienced a near-total collapse, with no individuals recorded in 2021 and 2023. In Alykaina and Greveno, subpopulations plummeted by 90–95 % between 2015 and 2016 and have since stabilized at critically low levels. To assess long-term viability, we conducted a Population Viability Analysis (PVA) using population matrix models for each subpopulation incorporating both the reproductive stages and transitional dynamics of the species. These models incorporated in-situ and ex-situ data on the species’ life cycle, alongside climatic parameters, primarily flooding events. The analysis identified secondary summer flooding during the flowering and fruiting period as the most critical threat. Climatic data show this phenomenon has intensified over the last 15 years, disrupting the plant’s reproduction. This is a unique case where precipitation, not drought, negatively affect the floristic composition of this habitat type. The threat is compounded by interspecific competition, with Eleocharis palustris encroaching in Livadies and Trifolium sp. in Alykaina. The PVA projects a high risk of extinction for V. oetaea within the next few decades if current biotic and abiotic pressures persist.