Medieval Pandemic Left Lasting Mark on European Forests

Radiocarbon dating of ancient trees reveals a hidden legacy of the mid-14th-century Black Death pandemic on European forest ecosystems. Researchers found a pulse of forest regeneration across Italy following the sharp decline in human populations. This recovery occurred as agricultural, grazing, and wood harvesting pressures significantly decreased.

The study focused on two oak species: evergreen holm oak on Montecristo Island and deciduous sessile oak in the Aspromonte mountains. Both populations showed a strong increase in tree establishment beginning in the early 1400s. This period directly followed the Black Death outbreak of 1347. Gianluca Piovesan, lead author from the University of Tuscia, stated that the human population collapse is visible in the age structure of Mediterranean forests.

On Montecristo Island, forest recovery was rapid, with a strong establishment peak within approximately one century. The mountain forests of Aspromonte showed slower regeneration. This delay may be due to more degraded ecosystems, harsher environmental conditions, and prolonged human disturbance before the pandemic. Radiocarbon dating allowed researchers to estimate tree ages even when traditional tree-ring dating was not possible.

Many old trees are hollow or decayed, making traditional methods unfeasible. Radiocarbon dating uses small fragments of inner wood to determine age. This method revealed that most individuals established between 1400 and 1650, a period marked by repeated plague outbreaks. Gianluca Quarta, a co-author from the University of Salento, noted the method's precision and accuracy for degraded wood samples.

The study also found that these oak populations include the oldest flowering trees in temperate regions. Holm oaks on Montecristo approached ages of up to 950 years, extending previous estimates by about two centuries. Tree size was not a reliable indicator of age, as some of the oldest trees had relatively slow growth and smaller diameters. Michele Baliva, a dendroecologist at the University of Tuscia, emphasized that longevity is about survival over centuries, not just growth.

These findings highlight the resilience of forest ecosystems. They suggest that reducing human pressure can trigger large-scale forest recovery. The research also underscores the importance of protecting ancient trees as natural heritage and ecological archives. These trees preserve evidence of past environmental and societal changes.