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

Abstract

In many perennial wind‐pollinated plants, the dynamics of seed production is commonly known to be highly fluctuating from year to year and synchronised among individuals within populations. The proximate causes of such seeding dynamics, called masting, are still poorly understood in oak species that are widespread in the northern hemisphere, and whose fruiting dynamics dramatically impacts forest regeneration and biodiversity. Combining long‐term surveys of oak airborne pollen amount and acorn production over large‐scale field networks in temperate areas, and a mechanistic modelling approach, we found that the pollen dynamics is the key driver of oak masting. Mechanisms at play involved both internal resource allocation to pollen production synchronised among trees and spring weather conditions affecting the amount of airborne pollen available for reproduction. The sensitivity of airborne pollen to weather conditions might make oak masting and its ecological consequences highly sensitive to climate change.

Investigating the relationship between climate, stand age, and temporal trends in masting behavior of European forest trees

“…In oaks, temperature and rainfall in spring strongly modulate crop size, through affecting phenological synchrony of flowering and pollination efficiency. As large-scale spatial synchrony of precipitation decreased over last 50 years (Table S2), it possibly contributed to the decreased synchrony in Quercus species (Bogdziewicz, Crone, et al, 2017;Koenig et al, 2015;Schermer et al, 2019). Interestingly, decreased synchrony in oaks might have important ecological consequences by dampening the predator satiation effect, the most broadly supported selective advantage of masting in these species (Kelly & Sork, 2002 (Satake & Iwasa, 2000.…”

From theory to experiments for testing the proximate mechanisms of mast seeding: an agenda for an experimental ecology

“…Another hypothesis relating weather and pollen limitation posits that warm, dry temperatures during the pollination period increases pollination efficiency through providing good conditions for pollen release and aerial diffusion (Schermer et al ). Thus, this aerial diffusion hypothesis predicts that warm temperatures and dry conditions should decrease pollen limitation through enhancing aerial pollen abundance and dispersal.…”

“…Pollen limitation may also be a consequence of unfavourable weather events like rainfall washing out pollen from the air column (García‐Mozo et al ). As in the case of phenological synchrony, such population‐wide pollination outcomes may interact with resource dynamics to produce mast years (Schermer et al ).…”

“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).…”