Environmental drivers of mast‐seeding in Mediterranean oak species: does leaf habit matter?

Abstract

Summary Understanding the proximate factors that govern the widespread mast‐seeding process is a question of considerable interest that remains poorly understood. The identity and effect of these factors may vary among coexisting species that differ in leaf habit, potentially resulting in temporally asynchronous patterns of seed production. In this study, we aim to identify the proximate causes of mast‐seeding using two oak species with contrasting leaf habit that coexist in southern Spain, the deciduous Quercus canariensis and the evergreen Q. suber. Simultaneously, we review the literature on environmental drivers of mast‐seeding in Mediterranean oaks, distinguishing between evergreen and deciduous species. Our results indicate that Mediterranean oaks are primarily sensitive to weather, mast‐seeding being strongly correlated with water availability and air temperature, mainly in the spring and summer. The two study oak species were affected by weather in quite different ways, most likely because of different abiotic requirements as well as contrasting functional strategies of resource use and biomass allocation. Specifically, annual seed production in Q. canariensis was more severely limited by drought than in Q. suber, but responded positively to warmer spring temperatures. Q. canariensis showed a large interannual variability, whereas Q. suber exhibited much more constant seed production. These two species also exhibited a very low level of synchrony in their temporal patterns of seed crop size, most likely due to phenological differences in the processes of flowering and seed maturation. Synthesis. Our results indicate that weather plays a crucial role as a proximate driver of mast‐seeding in Mediterranean oaks. We hypothesize that the current abundance of co‐occurring species that differ in leaf habit could be altered under future climate change scenarios. The decline of seed production with drier conditions will be potentially greater in deciduous species, particularly those inhabiting wetter sites. Alternatively, the expected warmer temperatures could negatively affect evergreen species as a consequence of their more conservative strategy of biomass allocation. Our findings suggest that understanding how species with different functional or phenological attributes adjust their reproductive abilities to weather may enable us to infer the effects of ongoing environmental changes on population recruitment and dynamics.