Flowering synchrony drives reproductive success in a wind-pollinated tree.

Synchronised and quasi-periodic production of seeds by plant populations, known as masting, is implicated in many ecological processes, but how it arises remains poorly understood. Flowering and pollination dynamics are hypothesised to provide the mechanistic link for the observed relationship between weather and population-level seed production. We report the first experimental test of the phenological synchrony hypotheses as a driver of pollen limitation in mast seeding oaks (Quercus ilex). Higher flowering synchrony yielded greater pollination efficiency, which resulted in 2-fold greater seed set in highly synchronised oaks compared to asynchronous individuals. Pollen addition removed the negative effect of asynchronous flowering on seed set. Because phenological synchrony operates through environmental variation, this result suggests that oak masting is synchronised by exogenous rather than endogenous factors. It also points to a mechanism by which changes in flowering phenology can affect plant reproduction of mast-seeding plants, with subsequent implications for community dynamics.