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

Abstract

• 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 non-linear, genus-specific relations. • Quercus and Fagus also differed as regards the secondary growth vs. 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.

Pollen limitation as a main driver of fruiting dynamics in oak populations

“…These results therefore suggest that the annual pollen amount, rather than pollen synchrony, determines pollination success and by extent fruiting success. Our results thus conflict with a recent work based on the same datasets than in our study (Lebourgeois et al 2018), in which the authors found no effect of annual airborne pollen amount on acorn production and concluded that their results supported the pollen synchrony hypothesis. However, their results and interpretation are questionable since they are drawn from poor estimates of pollen amount and synchrony at the fruiting sites (Appendix S2, and Table S4) and they did not directly test the effect of pollen synchrony on fruiting.…”

“…Contrary to the work of Lebourgeois et al . () that was based on the same pollen and acorn datasets as in our study, we considered that the two datasets cannot be directly crossed. Indeed, based on their method we found that annual oak airborne pollen amount as well as pollen synchrony were poorly estimated at the acorn sites (Appendix and Table ).…”

Ecohydrological modelling with EcH2O‐iso to quantify forest and grassland effects on water partitioning and flux ages

“…However, results are broadly consistent between years, and the simulation confidence interval brackets the observation values ( Figure S1). Notice that leaf allocation is very consistent between years; however, observation of fruit production shows high variability, suggesting that the stem and fruit pool might be a buffer in the model or capture phenological interannual dynamics unrelated to climate (Lebourgeois et al, 2018), and these detailed physiological aspects are not captured by the model. Figures S2 and S3), along with the root and stem allocation factors, and the associated sensitivity of LAI.…”

“Green pointillism”: detecting the within-population variability of budburst in temperate deciduous trees with phenological cameras

“…In some temperate angiosperms (e.g. deciduous oaks), the timing of flowering, which is closely related to the flushing-out of leaf buds (Franjic et al , 2011), influences the production of fruits (Lebourgeois et al , 2018; Schermer et al , 2019). This makes budburst an essential trait for the tree functioning, a trait subject to natural selection (Ducousso et al , 1996; Savolainen et al , 2007).…”