The hidden climate threat to Europe’s forests and why reproduction matters
Michal Bogdziewicz
Adam Mickiewicz University
DOI: 10.25453/fpprize.32065794
Growth decline in European beech associated with temperature-driven increase in reproductive allocation (PNAS, 2025)
“We have uncovered a previously hidden mechanism by which climate change can affect forests, helping us better predict and protect the future of these ecosystems”
Forests sit at the heart of planetary health. They store vast amounts of carbon, regulate water cycles, sustain biodiversity, and support human societies. Yet we often think about climate change impacts on forests in relatively simple terms: hotter temperatures, more droughts, more fires, and rising tree mortality. These threats are real. But our research reveals a quieter and more subtle danger that has largely gone unnoticed. One that is already reshaping Europe’s most widespread forest tree.
A hidden problem: when warming makes trees reproduce too often
Our research focuses on European beech, a species that forms the backbone of temperate forests across much of Europe. These forests are essential for biodiversity, timber production, and climate mitigation. For decades, scientists have documented drought-driven declines in beech growth, especially in southern regions. But in the United Kingdom, where drought has not intensified, we discovered something unexpected: beech trees are growing significantly less than they did just a few decades ago.
The cause is surprising; it is reproduction.
Many trees, including beech, do not produce seeds every year. Instead, they rely on a strategy known as mast seeding: synchronized bursts of massive seed production separated by several low-seed years. This strategy evolved because it improves pollination and overwhelms seed predators, ensuring that at least some seeds survive to become new trees. For decades, mast seeding followed steady rhythms triggered by weather cues. But climate warming has disrupted those cues. Warmer summers now trigger flowering more often, pushing trees to reproduce more frequently than in the past. At first glance, this might seem like good news — more seeds should mean more regeneration. But trees operate on limited internal energy budgets. Every seed produced comes at a cost.
Our study, based on a unique 43-year dataset combining seed production and tree-ring growth, shows that more frequent reproduction has drained trees’ stored resources. As a result, beech growth has declined by 28% since the mid-2000s — even in the absence of increased drought. This creates a dangerous feedback loop: reduced growth means less carbon uptake, smaller trees in the future, and ultimately reduced capacity to reproduce successfully.
Even more concerning, the shift away from synchronized seed production means trees actually produce fewer viable seeds despite flowering more often. Forests are now facing a “perfect storm”: slower growth, reduced carbon capture, and poorer regeneration.
This is a powerful reminder that climate change can affect ecosystems in indirect and unexpected ways. If we only look for direct climate impacts, we risk missing critical processes that determine the future of the biosphere.
Actionable solutions
Our findings provide knowledge that can reshape how we manage and protect forests.
First, our research highlights the urgent need to integrate reproduction into forest monitoring and modelling. Today, most forest models focus on growth, mortality, and carbon storage. Reproduction — the process that determines whether forests persist across generations — is often ignored. Our results show that this omission can lead to underestimating climate risks.
Second, forest management and conservation strategies must account for declining regeneration potential. If trees produce fewer viable seeds, natural forest recovery after disturbances becomes less reliable. This has major implications for reforestation and climate mitigation strategies that rely on forests as long-term carbon sinks.
Third, long-term ecological monitoring must be expanded and supported. Our study was only possible because researchers began monitoring beech seed production in 1980. Without decades of data, this hidden climate impact would have remained invisible. Sustained investment in ecological monitoring is essential infrastructure for planetary stewardship.
Finally, our work underscores the importance of climate mitigation itself. The mechanism we identified is driven by warming. Slowing climate change remains the most effective way to protect forest ecosystems at scale.
Real-world impact
Our research has already begun to reshape scientific understanding of forest responses to climate change. By demonstrating a previously unrecognized pathway linking climate warming to declining tree growth, it provides a missing piece in the puzzle of forest vulnerability.
This insight is now being incorporated into broader research efforts across Europe and beyond. Scientists are beginning to investigate whether similar reproduction-driven growth declines are occurring in other species and regions. Early evidence suggests that climate-driven changes in reproduction are widespread.
The implications extend beyond ecology. Forest carbon uptake is a cornerstone of global climate mitigation strategies. If forests grow more slowly than expected, their capacity to store carbon may be overestimated. By improving predictions of forest productivity and regeneration, our work contributes directly to more realistic climate planning. At scale, this knowledge can inform forest policy, climate models, and international climate agreements that rely on forests as nature-based solutions.
Advancing planetary boundary science
Planetary boundary science aims to define the limits within which humanity can safely operate. Forests are central to several of these boundaries, including climate change, biosphere integrity, and land-system change.
Our research advances this field by revealing how climate change can destabilize forest systems through indirect biological mechanisms. It demonstrates that the functioning of Earth’s systems depends not only on physical processes but also on complex ecological interactions.
If warming alters the balance between growth and reproduction, forests may lose resilience long before widespread dieback becomes visible. Detecting these early warning signals is essential for maintaining Earth within a safe operating space. By uncovering a hidden driver of forest decline, our work helps bridge the gap between ecological processes and planetary-scale sustainability. It shows that safeguarding forests requires understanding the full life cycle of trees: from growth to reproduction to regeneration.
Looking forward
Forests have long been viewed as allies in the fight against climate change. They remain so. But our research shows that their ability to help us depends on processes we are only beginning to understand.
The most exciting aspect of this work is its potential to change how we think about forests and climate change. By revealing a hidden vulnerability, we can act earlier and more effectively. We can improve forest management, refine climate models, and strengthen conservation strategies.
The story of the European beech is likely just the beginning. Around the world, forests are responding to climate change in ways we are only starting to detect. With continued research, monitoring, and collaboration, we can better understand these changes — and work to ensure that forests remain a cornerstone of planetary health for generations to come.
While scientific literature has documented the numerous environmental impacts of lithium mining, identifying 15 distinct impacts spanning environmental, social, and economic dimensions, our research has shown that local and Indigenous communities possess a more holistic and relational understanding of these changes. Their knowledge systems connect ecological processes with social, cultural, and spiritual dimensions of life. Community members clearly describe how mining activities affect water availability, soil conditions, biodiversity, and, ultimately, their livelihoods and ways of life. The first step of the policy analysis was to develop a set of locally grounded indicators of environmental change, derived from community observations and experiences. These indicators provide valuable, context-specific insights that complement conventional scientific metrics.
When analyzed in relation to the SDGs, we found that these local indicators could contribute to all SDGs except SDG 14 (Marine life), which is not directly relevant to this inland region. Moreover, many local indicators simultaneously relate to multiple SDGs, reflecting the integrated nature of local knowledge. Our research also uncovered a critical gap: no local indicators associated with the loss of ancestral knowledge could be directly linked to existing SDG targets. This highlights a significant limitation in current global frameworks, which often fail to capture the erosion of cultural heritage and knowledge systems as a key dimension of sustainability.
In response, our work proposes actionable solutions to bridge these gaps. First, we advocate for the systematic inclusion of local and Indigenous knowledge in environmental assessment and monitoring processes. This can be achieved by co-developing indicators with communities, ensuring that their perspectives are not only acknowledged but also actively shape decision-making. Second, we emphasize the need to strengthen consultation and participation mechanisms. Current processes are often insufficient, either in scope or implementation, to guarantee meaningful engagement. We propose more equitable, transparent, and culturally appropriate consultation frameworks that respect the rights of Indigenous Peoples and local communities. Third, our research supports the integration of these insights into policy and industry practices. By aligning local indicators with global sustainability frameworks, decision-makers can design more context-sensitive and socially just interventions. This approach also facilitates the scaling of solutions, as it provides a model for incorporating diverse knowledge systems into sustainability governance.
Our work has already begun to generate tangible impacts. Empirically, it documents for the first time in this region the perspectives of local and Indigenous voices about decisions that directly reshape their territories. Methodologically, it offers a replicable framework for documenting and incorporating community-based knowledge into sustainability assessments.
Beyond academia, we are actively contributing to policy discussions and public debates. Through policy briefs, technical reports, and direct engagement in local territories, we are promoting the recognition of Indigenous rights and the inclusion of local perspectives in mining governance. These efforts aim to influence national legislation and industry standards, ensuring that future development pathways are more inclusive and equitable. More broadly, our research advances planetary boundary science by emphasizing that environmental sustainability cannot be achieved without social justice. The concept of a “safe operating space” for humanity must include not only biophysical limits but also the rights, knowledge, and well-being of the communities most directly affected by global transitions. In the context of lithium extraction in the Andean salt flats, this means rethinking the energy transition as not only a technological shift but also a socio-political transformation. It requires moving beyond extractive mindsets toward more participatory, inclusive, and context-aware approaches.
Ultimately, our work calls for a redefinition of sustainability—one that recognizes the value of diverse knowledge systems and ensures that the transition to a low-carbon future does not come at the expense of those who have historically contributed least to global environmental crises. By integrating local and Indigenous knowledge into global frameworks, we can move closer to a truly just and sustainable pathway that respects both planetary boundaries and human dignity.