Dave Kelly, Jakub Szymkowiak, Andrew Hacket-Pain, Michał Bogdziewicz

Interannual variability of seed production, known as masting, has far-reaching ecological impacts including effects on forest regeneration and the population dynamics of seed consumers. It is important to understand the mechanisms driving masting to predict how plant populations and ecosystem dynamics may change into the future, and for short-term forecasting of seed production to aid management. We used long-term observations of individual flowering effort in snow tussocks (\emph{Chionochloa pallens}) and seed production in European beech (\emph{Fagus sylvatica}) to test how endogenous resource levels and weather variation interact in driving masting. In both species, there was an interaction between the weather cue and plant resources. If resource reserves were high, even weak temperature cues triggered relatively high reproductive effort, and depleted resources suppressed reproduction even in the presence of strong cues. Thus, resource dynamics played dual roles of both suppressant and prompter of reproduction, allowing plants to fine-tune the length of intervals between large-seeding years regardless of variable cue frequency. The strong interaction between resource reserves and weather cues has immediate application in mast forecasting models increasingly important for global afforestation efforts. Moreover, the important role of resource reserves in the plant response to weather cues will dictate the masting responses to climate change.