Drivers of ash (Fraxinus excelsior L.) natural regeneration spread into suboptimal sites – Refugee or dead end?

Abstract Ash disease caused by ascomycete fungus Hymenoscyphus fraxineus leads to the retreat of ash, particularly in ash-dominated stands characterized by moist, fertile, and neutral soils. Thus, it has a more severe impact on species regeneration and survival in ash optimal sites. We aimed to investigate the joint effects of seed dispersal limitation triggered by the distance from seed source, as well as soil fertility, browsing, and understory vegetation on ash natural regeneration in optimal and neighboring suboptimal sites. We examined ash regeneration within 40 circular plots (25 m2) in Western Poland along soil fertility gradient and increasing distance from seed source (0–100 m). We confirmed the seed dispersal limitation of ash regeneration. We found that the increase of distance from seed source increases ash natural regeneration (both of