Medieval pandemic left a hidden legacy in Europe's oldest trees

Medieval pandemic left a hidden legacy in Europe's oldest trees Lisa Lock Scientific Editor Andrew Zinin Lead Editor A new study published in the Proceedings of the National Academy of Sciences demonstrates how radiocarbon dating can reveal the maximum lifespan of Mediterranean hardwoods, uncovering hidden links between human history and long-term ecosystem dynamics. By analyzing mature and ancient oak trees across Italy, researchers found that a millennium of age is attainable from the Mediterranean coast to mountain environments. These are the oldest Mediterranean hardwood forest ecosystems on record, and they showed a pulse of regeneration after the mid-14th-century plague, when human populations collapsed and pressure on landscapes abruptly declined. Trees as witnesses of a medieval pandemic The team focused on two oak species growing at opposite ends of the Mediterranean environmental gradient: - evergreen holm oak (Quercus ilex) on Montecristo Island - deciduous sessile oak (Quercus petraea) in the Aspromonte mountains in southern Italy Despite their different ecological settings—island versus high-elevation mountain—both populations showed a strikingly similar pattern. Radiocarbon dating revealed a strong pulse of tree establishment beginning in the early 1400s, just a few decades after the Black Death outbreak of 1347. This timing coincides with a period of dramatic population decline across Europe, which reduced agriculture, grazing and wood harvesting. "When human pressure decreases, forest ecosystems can recover in a few decades," explained Gianluca Piovesan, professor of global changes and rewilding at the Department of Ecological and Biological Science at the University of Tuscia in Italy and lead author of the study. "We can literally see the imprint of the human population collapse following the Black Death in the age structure of Mediterranean forests." On Montecristo Island, the recovery was rapid, with a strong establishment peak within about a century. In contrast, the mountain forests of Aspromonte showed slower, more delayed regeneration, likely due to a more degraded forest ecosystem, harsher environmental conditions and prolonged human disturbance before the Black Death pandemic in medieval times. Radiocarbon dating uncovers hidden forest history Determining the age of ancient trees is notoriously difficult. Many old trees are hollow, decayed or lack clear annual rings, making traditional tree-ring dating unfeasible. Radiocarbon dating, however, allows researchers to estimate age using small fragments of inner wood, even when anatomical elements are decaying. Using this approach, the researchers reconstructed age distributions for both oak populations and found that most individuals established between 1400 and 1650—a period marked by repeated plague outbreaks across the Mediterranean region. "The method of radiocarbon dating makes it possible to obtain highly precise and accurate absolute ages even from degraded and very small wood samples," said Gianluca Quarta, professor of applied physics at the Department of Mathematics and Physics at the University of Salento in Italy and co-author of the study. "The large number of data collected across different contexts, combined with robust statistical interpretation, made it possible to achieve the results presented in this study." The research also highlights the technological advances behind these findings. "This is another important outcome of the long-standing collaboration among the applied physics group at the University of Salento, the University of Tuscia, the University of Nevada and the Arma dei Carabinieri," said Lucio Calcagnile, director of the CEDAD laboratory (Center of Applied Physics, Dating and Diagnostics) at the Department of Mathematics and Physics at the University of Salento and co-author of the study. "The results were made possible in part by the new particle accelerator for radiocarbon dating recently installed at CEDAD, which represents state-of-the-art technology at the international level." Unexpected tree longevity Radiocarbon dating also revealed that these oak populations include the oldest flowering trees in temperate regions. Holm oaks on Montecristo were found to approach near-millennial ages—up to about 950 years—extending previous estimates for Mediterranean evergreen trees by roughly two centuries. The study also confirms that tree size is not a reliable indicator of age. Some of the oldest individuals showed relatively slow growth and smaller diameters compared with younger trees. "Longevity is not about growing fast or becoming large," said Michele Baliva, dendroecologist at the University of Tuscia and co-author of the study. "It's about surviving over centuries under changing environmental conditions." The discovery of such long-lived trees also underscores the urgency of protecting them. The Biodiversity Group of the Carabinieri Forestali (CUFAA), which manages the protected areas of Montecristo and Aspromonte where these millennia-old trees were found, has long been involved in safeguarding these unique forest ecosystems. "These trees represent an irreplaceable natural heritage," said Raffaele Manicone, general of the Carabinieri Forestali, head of the Biodiversity Group and co-author of the study. "Their conservation is mandatory, especially in the face of growing threats to biodiversity posed by global changes." "In Montecristo, we are investing significant effort to protect the ancient oak population from damage caused by feral goats," added Giovanni Quilghini, colonel of the Carabinieri Forestali, commander of the Montecristo Reserve and co-author of the study. "At the same time, research like this is crucial to deepen our knowledge of ancient trees, helping us understand their dynamics and providing the scientific basis needed to better protect them in the future." A new perspective on rewilding The researchers argue that these insights are highly relevant today as policymakers seek effective strategies for forest restoration and climate adaptation. In a world facing climate change and biodiversity loss, the study suggests that reducing human pressure on landscapes could once again trigger large-scale forest ecosystem recovery—just as it did nearly 700 years ago. "Biodiversity conservation is a strategic priority for the future, and it is essential that we continue to build stronger scientific knowledge to support it," concludes Alessandro Chiarucci, professor of applied botany at the University of Bologna. "Protected areas are fundamental for conserving biodiversity, but they are also living laboratories of the Earth, helping us uncover how interactions between our species and nature have evolved over the centuries." The findings highlight the resilience of forest ecosystems and their ability to recover when human pressure is reduced. They also suggest that ancient trees play a key role as ecological archives, preserving evidence of past environmental and societal changes. "The range and breadth of stories that ancient trees can tell us has been enriched by the cutting-edge approaches for radiocarbon dating used in this work, linking a tragic moment in human history to the flourishing of wilderness," said Chuck Cannon, director of the Applied Research Center for Tropical Plant Conservation at the Xishuangbanna Tropical Botanical Garden in China and co-author of the study. "These ancient trees are truly witnesses of great events in the distant past." Publication details Gianluca Piovesan et al, Ancient oaks reveal rewilding of Mediterranean forests after the Black Death, Proceedings of the National Academy of Sciences (2026). DOI: 10.1073/pnas.2529341123 Journal information: Proceedings of the National Academy of Sciences Provided by University of Tuscia