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