An isolated population of relict Pterocarya fraxinifolia at the NW limit of its distribution range

Since the mid-Miocene, climatic cooling and Quaternary climatic oscillations have significantly reduced plant diversity. Consequently, Cenozoic plant communities across the Northern Hemisphere experienced range contractions, surviving as relict floras in southern refugia. Anatolia has served as a critical refugium during Pleistocene glaciations due to its geographic and paleoclimatic features, thus maintaining a rich relict flora. This study evaluates the overlooked population of the Cenozoic relict tree Pterocarya fraxinifolia along the Panayır River in Northwestern Thrace, Türkiye, addressing the anthropogenic and environmental threats impacting this disjunct population. Field surveys were conducted in 2024 to examine the population, outline its floristic composition, and assess associated threats. Furthermore, the climatic characteristics of the habitat were evaluated using high-resolution CHELSA climate data, which were validated against local meteorological station records through regression analyses and error metrics in R. This population is notable because it represents the westernmost known distribution of the species and is the closest population to Europe, where it formed part of mixed evergreen and deciduous forests during the Miocene and Pliocene periods. This small population is strictly restricted to the main course of the river and is established on the alluvial soils overlying the Quaternary alluvial deposits. This small area is surrounded with a plant community dominated by moisture-demanding species, highlighting the tree’s strong reliance on humid riparian environments. The Panayır River dunes and their surrounding landscape has already been proposed for protection in the literature due to its habitat diversity, biodiversity, and the presence of threatened rare and endemic species. Additionally, it is home to one of the rare remaining populations of the important relict species Pterocarya fraxinifolia in Anatolia. Despite the threats posed by summer visitors, litter, overgrazing, logging, potential sea level rise, and the proposed nuclear power plant, the Panayır River lacks any formal protection status. Relict plant species offer valuable insights into both past and present evolutionary and biogeographical processes; therefore, the conservation of the Panayır River population is of vital importance due to these critical ecological and research aspects.