Assessing the roles of temperature, carbon inputs and airborne pollen as drivers of fructification in European temperate deciduous forests

We aimed at identifying which drivers control the spatio-temporal variability of fruit production in three major European temperate deciduous tree species: Quercus robur , Quercus petraea and Fagus sylvatica . We analysed the relations of fruit production with airborne pollen, carbon and water resources and meteorological data in 48 French forests over 14 years (1994–2007). In oak, acorn production was mainly related to temperature conditions during the pollen emission period, supporting the pollen synchrony hypothesis. In beech, a temperature signal over the two previous years eclipsed the airborne pollen load. Fruit production in Quercus and Fagus was related to climate drivers, carbon inputs and airborne pollen through strongly nonlinear, genus-specific relations. Quercus and Fagus also differed as regards the secondary growth versus fructification trade-off. While negative relationships were observed between secondary growth and fruit production in beech, more productive years benefited to both secondary growth and reproductive effort in oak.