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

Abstract

Highly variable and synchronised production of seeds by plant populations, known as masting, is implicated in many important ecological processes, but how it arises remains poorly understood. The lack of experimental studies prevents underlying mechanisms from being explicitly tested, and thereby precludes meaningful predictions on the consequences of changing environments for plant reproductive patterns and global vegetation dynamics. Here we review the most relevant proximate drivers of masting and outline a research agenda that takes the biology of masting from a largely observational field of ecology to one rooted in mechanistic understanding. We divide the experimental framework into three main processes: resource dynamics, pollen limitation and genetic and hormonal regulation, and illustrate how specific predictions about proximate mechanisms can be tested, highlighting the few successful experiments as examples. We envision that the experiments we outline will deliver new insights into how and why masting patterns might respond to a changing environment.

On the need to evaluate costs and benefits of synzoochory for plant populations

“…Moore and Dittel (2020) further added that ‘masting may in fact be the reason the interaction can be mutualistic’. We agree that mast years (synchronous production of large seed crops: Bogdziewicz, Ascoli, et al, 2020; Kelly & Sork, 2002; Pearse, Koenig, & Kelly, 2016) can tilt plant–scatterhoarder interactions towards mutualism. We briefly discuss this possibility in Bogdziewicz, Crone, et al (2020), giving pros and cons for the occurrence of such shifts in our study system.…”

Extreme summer heat and drought lead to early fruit abortion in European beech

“…In our case, for European beech, early browning or loss of leaves ("defoliation") as a consequence of the extremely hot and dry summer likely led to a shortage of resources, although other factors, e.g. genetic expression or hormonal regulation, can play a role as well 32 . www.nature.com/scientificreports www.nature.com/scientificreports/ The assumed biennial mast cycle in European beech can be interrupted by environmental factors, as seen in the fruiting levels from 2006 to 2018 (Fig.…”

“…The underlying biennial cycle may be partly influenced by weather conditions during the vegetation period and the summer conditions in previous summers, and partly by resource dynamics of the trees. As aforementioned, other mechanisms, such as gene expression or hormonal regulation might play a role as well 32 . Fruit development for beech seems to be very resource intensive and therefore, trees typically do not develop flower buds for the next year during summers of successful mast years, as seen in the pollen data for Switzerland (Figs.…”

Climate warming disrupts mast seeding and its fitness benefits in European beech

“…Similar changes are likely to occur in other masting species, with other negative conservation consequences 53 , but such long-term datasets as the one reported here are extremely rare 27 . Thus, experiments to better understand the mechanisms underlying masting, and consequently better predict the consequences of a changing climate for plant reproductive patterns and global vegetation dynamics, should become a research priority 54 . The net benefits of climate warming in the European beech system studied here accrue largely to an invertebrate seed predator, which suggests that ecological interactions may determine the realworld consequences of global change.…”