Forest Biology Center

Our recent study focusing on rowan trees (Sorbus aucuparia) sheds light on how these trees optimize their reproductive efficiency through synchronized and variable seed production.

Mast seeding is a strategy where trees forego reproduction in some years to produce a bumper crop of seeds in others, often in sync with neighboring trees. This boom-and-bust cycle has significant impacts on ecosystems, influencing food webs and nutrient cycling. But why do trees adopt this seemingly risky strategy? The key lies in reproductive efficiency—the effectiveness of converting resources into successful offspring. By synchronizing large seed production events, trees can overwhelm seed predators, ensuring that a higher proportion of seeds escape being eaten. Additionally, synchronized flowering increases pollination success, as pollinators are more likely to visit trees when many are in bloom simultaneously.

In this study, we tracked 209 rowan trees over 23 years, recording their fruit production patterns. We used genetic analysis to determine which seedlings originated from which trees, allowing them to measure each tree’s reproductive success in terms of the number of established offspring. The findings revealed that trees with high interannual variability in fruit production had higher reproductive efficiency, but only if they synchronized their fruiting with other trees. These trees benefited from the economies of scale that mast seeding provides, such as reduced seed predation and improved pollination. Conversely, trees that varied their fruit production but did so out of sync with others experienced lower reproductive efficiency. They missed out on the benefits of synchrony while still bearing the costs associated with intermittent reproduction. Interestingly, trees that reproduced regularly but did not synchronize with others achieved the highest reproductive efficiency per fruit. However, these trees typically had lower overall fecundity—they produced fewer fruits on average. This suggests a trade-off between maximizing reproductive efficiency and producing a large number of seeds.

By linking long-term ecological data with genetic analyses, we provided compelling evidence that mast seeding enhances reproductive efficiency beyond the seed stage. This means that the benefits of mast seeding persist through seedling establishment and contribute to the evolutionary success of this reproductive strategy. These insights help explain why mast seeding has evolved and persisted in various tree species. They highlight the delicate balance trees must strike between synchronizing with their neighbors to gain collective benefits and managing the individual costs associated with variable reproduction. Read the full story: https://onlinelibrary.wiley.com/doi/10.1111/ele.14514

Mast seeding, or masting, is a fascinating reproductive strategy observed in many perennial plants, where individuals within a population produce seeds in highly variable quantities from year to year. This synchronized fluctuation in seed production among plants has long intrigued ecologists, primarily because it offers a significant survival advantage: it helps reduce the impact of seed predators. By alternating between years of seed scarcity and abundance, plants can effectively “starve” predators in low-yield years and “satiate” them in high-yield years, ensuring that more seeds survive to germinate.

The relationship between masting and environmental conditions, particularly weather, is well-established. Plants often synchronize their masting events in response to  weather patterns, leading to widespread seed production across species. While this interspecies synchronization could theoretically enhance the predator satiation effect, it has not been thoroughly studied until now.

In a recent study, we tested this hypothesis by analyzing 23 years of data on seed production and pre-dispersal seed predation in three North American oak species: Quercus rubra (red oak), Quercus alba (white oak), and Quercus montana (chestnut oak). The study revealed that weather patterns, particularly those in spring and summer, were  correlated with masting events in all three oak species. This correlation led to varying degrees of synchronization within each species, ranging from 21% to 38%.

Interestingly, the study found that this intraspecific synchrony—where individuals of different species mast together—played a crucial role in reducing seed predation. For Q. rubra and Q. alba, synchronized masting resulted in efficient starvation of seed predators, significantly reducing seed losses. However, for Q. montana, it was the community-wide masting events, where multiple oak species produced seeds simultaneously, that were necessary to satiate the predators effectively.

These findings provide rare empirical evidence supporting the idea that synchronized masting within a species can enhance reproductive success by minimizing seed losses to predators. Moreover, the study suggests that forests with diverse oak species might have better regeneration potential due to the increased likelihood of community-wide masting events. This insight could inform forest management practices, emphasizing the importance of species diversity to boost seed survival and forest regeneration.

Ever wondered why some years your favorite forest is overflowing with beech nuts, and other years it’s almost barren? This feast-or-famine cycle, known as masting, is not just random. Our recent research reveals a fascinating pattern: European beech trees are synchronizing their seed production across vast distances, but intriguingly, they do so differently for bumper crop years compared to lean ones.

Masting refers to the high variation in seed production that some perennial plants exhibit from year to year. Imagine a forest where, one year, beech trees are heavy with seeds, and the next, they’re nearly bare. This phenomenon isn’t just a local quirk; it can happen simultaneously across regions spanning hundreds of kilometers. Researchers have been curious to understand whether these peaks (high seed years) and troughs (low seed years) in seed production are synchronized differently.

We delved into this question by studying 99 populations of European beech trees (Fagus sylvatica) across Europe. We discovered that while mast peaks (years of high seed production) are synchronized up to 1000 kilometers apart, the years of seed scarcity are synchronized across even larger distances, up to 1800 kilometers.

This spatial synchrony is more concentrated in northeastern Europe for mast peaks, while seed scarcity spans almost the entire range of the species. This extensive synchrony in low seed years means that when beech trees experience a bad year, it’s felt widely, creating resource famines that can ripple through ecosystems.

Such extensive synchrony in seed scarcity has important implications. It can lead to resource pulses or famines, impacting food webs significantly. Animals that rely on beech seeds for food may face widespread shortages, affecting their populations and behavior. This, in turn, can influence predator-prey dynamics, biodiversity, and even forest health.

Understanding these patterns is crucial in the context of climate change. As weather patterns shift, the synchrony in masting may alter, potentially leading to more frequent or severe resource pulses and famines. This can affect not only the plants and animals directly involved but also the broader ecological and climatic systems.

Our recent paper on mast seeding in perennial plants presents a model that integrates proximate factors (environmental variation, weather cues, resource budgets) with ultimate drivers (predator satiation, pollination efficiency). This model illustrates how the relationships between mast seeding and weather influence species’ responses to climate warming, ranging from no change to reduced interannual variation or reproductive failure. The role of environmental prediction as a driver of mast seeding is being reassessed; future studies need to estimate the accuracy of these predictions and the benefits they confer. Understanding how mast seeding adapts to shifting environmental conditions is now a central question in plant adaptation to climate change.

Our recent paper shows that in birds, anti-predator responses toward previously unfamiliar sounds (samples of punk rock songs) can be socially transmitted among territorial individuals, with naïve birds learning through the association of unfamiliar sounds and alarm calling reactions of conspecific neighbors. Moreover, once learned soon after nestlings hatching, the anti-predator response of parents can be retained until the end of nestlings rearing period. Thus, at the beginning of a pivotal phase of a breeding cycle, birds can acquire a vital life skill—recognition of novel risk cues—from conspecific neighbors, which they can incorporate into their own repertoire of anti-predator behaviors and use later when taking care of own nestlings. Jointly, these results demonstrate social learning as one of the mechanisms explaining the widespread abilities of animals to assess predation risk via acoustic signals. Read the full story here: https://doi.org/10.1007/s10071-024-01858-6

Our new paper explores how seed production in perennial plants, like European beech (Fagus sylvatica), synchronizes across vast distances, affecting ecosystem functions. The study reveals that the summer solstice serves as a celestial cue, triggering synchronized responses to weather conditions among widely separated populations of European beech. This ‘starting gun’ initiates ecological events with high spatial synchrony across the continent, highlighting the significance of celestial cues and weather coordination in shaping ecosystem dynamics.
Read the full story: https://rdcu.be/dADZx

Masting, the synchronized seed production among plants, is often seen as a reproductive strategy. But is it inherited? We studied 110 Sorbus aucuparia L. trees for 22 years to find out. We discovered that trees with similar genetics and growing conditions shared similar reproductive patterns. Also, trees of similar sizes had comparable fluctuations in fruiting from year to year, influenced partly by genetics. These findings suggest that masting behavior is inherited and can adapt to nature’s challenges, giving us new insights into how plants reproduce and thrive.

New study in European Journal of Forest Research dissects 22 years of rowan tree fecundity, emphasizing the pivotal role of DBH and the dominance of light availability. Notably, neighborhood crowding unveiled a correlation with pollinator competition. This research advances seed production ecology understanding, offering insights for effective fruit supply management. Read the full study:
https://link.springer.com/article/10.1007/s10342-024-01661-5

New paper in Ecology shows that reproductive performance of Wood Warblers – small, ground-nesting songbirds – is much lower in years following mast seeding than in years preceded by mast failures, as mast seeding indirectly increases predation pressure on Wood Warbler nests. Moreover, matrix population models revealed that regional variation in mast seeding frequency is a possible explanation for divergent population trends of Wood Warblers in different regions of Europe. The paper can be found here: https://doi.org/10.1002/ecy.4227

New paper in Nature Communications takes 517 plant species and links their interannual variation of seed production with functional traits. While interannual variation in seed production is highest in temperate and boreal zones, our analysis controlling for environment and phylogeny indicates that masting is more frequent in species that invest in tissue longevity.

There is a write-up on that paper in the Nature blog, and the paper is here.