Irregular fruiting in Fraxinus excelsior

Abstract. Data of fruit‐set and fruit production of Fraxinus excelsior (ash) at two sites in the archipelago of Stockholm, Sweden, were recorded over six years (1980‐85), with particular emphasis on the fruiting tendency of individual trees. The aim was to determine the grounds for the irregularity of fruiting. There was no support for the assumption that irregular fruiting originates as a consequence of the fruiting tendency being resource limited. The probability of fruiting in a certain year was neither negatively related to previous fruiting years, nor positively related to climatically favourable years. Seeds were infested by the monophagous moth larva Pseudar‐gyrotoza conwagana. An increased seed survival was noted in times of large seed crops, indicating seed predator satiation. Date of leafing the preceding year determined whether individual trees fruited or not. This relationship may have significance in synchronizing the fruit production of ash trees.