Longitudinal population dynamics of Mediterranean-Atlantic Arbutus during the last 30 ka

The current distribution of the genus Arbutus in the Old World prompts questions about its long-term population dynamics, location and extent of refuge areas, and modern vulnerability in relation to climate change and human activity. Our work aims to address these questions by combining modern occurrence data with a comprehensive survey of pollen and macrofossil records. Range maps of past distribution have been produced for the last 32 ka to investigate geographical trends in population dynamics and the timing of the appearance of Arbutus across different biogeographical regions. In the Atlantic domain, Arbutus has been consistently present during the last 32 ka, even during the Last Glacial Maximum. In the central and eastern Mediterranean regions, it progressively increased since the beginning of the Holocene, appearing along the coasts of the Black Sea and in the Levant during the Middle Holocene. In addition, the dynamics of Arbutus in a number of peripherals stands (Ireland, Canary Islands, Cyrenaica, Crimea, and Black Sea coasts) is discussed. The palaeobotanical evidence suggests that the delayed emergence of eastern populations and peripheral stands in the fossil record may be ascribed to a very low population density, rather than to a sequential migration process from the western sectors of the range. The comparison of fossil records and modern occurrences highlights an overall temporal continuity between long-term persistence areas and current centers of gravity and calls for density-weighted ecological models that may contribute to an informed assessment of conservation actions and strategies.