Unveiling the Hidden Crisis: Climate Change and Tree Fecundity
Michał Bogdziewicz
Forest Biology Center, Adam Mickiewicz University in Poznań, Poland
“Climate change disrupts forest regeneration, risking ecosystem health. Understanding this process is crucial for forest preservation”
Forests face escalating pressures driven by climate change. Large-scale mortality, known as forest die-offs, is increasingly common due to intensifying droughts, fires, and insect infestations. The ability of future forests to sustain biodiversity and provide ecosystem services, such as storing carbon, water management and climate regulation, hinges on the regeneration potential of trees, which must keep pace with accelerating mortality rates. However, current forest biology primarily concentrates on tree growth and survival, overlooking the crucial aspect of tree reproduction. The emphasis on growth and survival lacks empirical support suggesting that fecundity (seed production) is any less significant. This focus on tree growth stems partly from the abundance of data available from long-term monitoring plots and tree cores that allow reconstruction of the past growth, which provide insights into growth patterns over decades. In contrast, data on fecundity accumulate slowly and require substantial investment, leading to a gap in our understanding of its role in population dynamics, especially in response to climate change. Our research aims to bridge this gap, highlighting the indispensable role of tree fecundity in ecology. Neglecting the ecology of tree fecundity jeopardizes management and conservation efforts, as insufficient supply of seeds for the growth of new trees can impede the efficient replacement of dead trees with living ones.
Understanding the reproductive responses of plants to climate change is further complicated by masting, the phenomenon of synchronized, variable seed production across individuals and populations. In masting plants, seed production fluctuates significantly between years, with periods of reproductive failure alternating with peaks many times greater than the long-term average. This phenomenon is widespread among long-lived plants, particularly trees. Masting optimizes tree reproduction by alternating periods of seed abundance and scarcity, which helps regulate seed consumption by starving and then satiating seed consumers such insects and rodents. Additionally, masting enhances pollination efficiency by concentrating flower production in large, synchronized events. Our research indicates that warming disrupts masting patterns, leading to a decline in interannual variation and synchrony of seed production—a phenomenon we term "masting breakdown." This disruption increases seed predation and pollen limitation, reducing reproductive potential, particularly in large trees, where fecundity may plummet by up to 80%. Such drastic reductions in fecundity can lead to unnoticed delayed loss of species – called extinction debts – over decades, given trees' long lifespans. Identifying this cryptic impediment to tree regeneration underscores the urgency of mitigation efforts. Alarmingly, foresters in Europe already report seed supply issues for their nurseries. Addressing this problem requires mainstream recognition of the effects of climate change on fecundity.
The masting breakdown identified by our research highlights a significant yet covert obstacle to tree regeneration. Untangling the complex ecological interactions that impact tree fecundity was a crucial first step; now, management strategies to mitigate the effects on viable seed production must be evaluated and implemented. Understanding species' responses to altered climatic conditions is essential for developing alternative management strategies. Our work exposes a major issue that might otherwise go unnoticed and provides a clear framework for action. For instance, declining pollination efficiency in large trees could be remedied by planting or preserving smaller members of the same tree species nearby. However, the positive effects of such strategies could be nullified by seed consumption if predation rates increase with tree density. The ecological crisis challenges traditional forest management approaches. To ensure forests continue to provide essential services to ecosystems and human society, immediate investigation into mechanisms leading to fecundity collapse and reversal options is imperative. This requires a deeper understanding of the mechanisms driving seed production at scales ranging from individuals to populations, as well as the impacts of climate change on these mechanisms. This stands as our research priority.
Photo 1. Starting from the top left corner: Jonathan Lageard, Michał Bogdziewicz, Dave Kelly, Jessie Foest, Andrew Tanentzap, Peter Thomas, Andrew Hacket-Pain.
