Environmental veto synchronizes mast seeding in four contrasting tree species

Synchronized and variable reproduction by perennial plants, called mast seeding, is a major reproductive strategy of trees. Resource budget models proposed that masting relies on the depletion of resources following fruiting events, which leads to temporal fluctuations in fruiting; while outcross pollination or external factors preventing reproduction in some years synchronize seed production among trees. We used seed production data for four species (Quercus ilex, Q. humilis, Sorbus aucuparia, Pinus albicaulis) to parametrize resource budget models of masting. Based on species life history characteristics, we hypothesized that pollen coupling should synchronize reproduction in S. aucuparia and P. albicaulis, while in Q. ilex and Q. humilis environmental veto should be a major factor. Pollen coupling was stronger in S. aucuparia and P. albicaulis than in oaks, while veto was more frequent in the latter. Yet, in all species, costs of reproduction were too small to impose a replenishment period. A synchronous environmental veto, in the presence of environmental stochasticity, was sufficient to produce observed variability and synchrony in reproduction. In the past, vetoes like frost events that prevent reproduction have been perceived as negative for plants. In fact, they could be selectively favored as a way to create mast seeding.