A new study used the Black Death as a natural experiment, finding that medieval farming fostered Europe's biodiversity.

We assume that nature would thrive when humans disappear, but a study of plant diversity across 100 European sites spanning 2,000 years tells a more counterintuitive story: when the Black Death swept through 14th-century Europe, killing a third of the population and emptying farmlands, plant biodiversity collapsed, recovering only when people started farming again.

Large-scale agriculture and farming of lands is thought to drive biodiversity decline, particularly over the last century. But when researchers look at pollen datasets (a repository of plant diversity) over longer timescales, biodiversity seemingly flourishes with human presence. Jonathan Gordon, a researcher at the University of York in the UK, and colleagues previously found that, as human population sizes grew and expanded their footprint over the last 12,000 years, so too did biodiversity.

While these opposing correlations are not inherently incompatible given different farming conditions in the past versus modern times, the result is counterintuitive. Gordon’s team used the Black Death mass mortality event as a testable scenario. “Our hypothesis was that, if humans were making Europe’s landscapes more biodiverse, then the sudden population collapses and associated abandonment of cultivated lands during the Black Death should have resulted in biodiversity losses,” writes Gordon in an email to Advanced Science News. “The sudden and relatively well documented falls in human population levels [make] the Black Death a useful ‘natural experiment’ for investigating questions of long-term human–nature relationships.”

In the 13th century, as more urban centers popped up and populations grew, agriculture evolved from a purely subsistence-based concept. What followed was the Black Death era in the 14th century, comprising the Great Famine (1315–1317 CE) as well as the Black Death (1347–1353 CE). Over this period, populations in different areas were decimated, with a third of the population dying off. Populations gradually recovered over the late 16th and 17th centuries, with agriculture then growing more specialized. How did biodiversity respond to the slump in population and cultivation and the eventual return of these human activities?

The research team used a European pollen dataset with 4,616 samples from the Common Era across 100 sites, such as bogs and lakes. Scientists can drill into the sediment layers at the bottom of wetlands, where pollen from tens of thousands of years ago is preserved. Each slice of the core, when dated using radiocarbon dating, can tell us what the vegetation landscape was during each specific period. Gordon and colleagues looked at temporal patterns of pollen types, and how these patterns shifted over landscapes with differing land use histories over the Black Death Era.

They recorded three historical phases from 0 to 1850 CE, where biodiversity was shaped by a confluence of societal, industrial and agricultural influences. In the first phase that spanned the beginning of the Common Era to 1300 CE, plant diversity in Europe increased. During this period, the Western Roman empire rose and fell, driving demand for agricultural systems with a wide variety of crops that could sustain growing populations and the military. Even in parts of Europe outside the reach of the empire, barley and rye were cultivated alongside animal husbandry. Overall, the landscape was a mosaic of habitats shaped by human impact and use. Cultivated plots were separated by wild heaths and woods, resulting in diverse agro-ecosystems.

In the second phase, from 1300 to 1450 CE, plant diversity plunged. More marginal settlements were abandoned in favor of larger, established ones where surviving communities concentrated. As human populations thinned out or collapsed across areas that were previously farmed, so too did biodiversity. Diversity declines were linked to sites where cereal pollen dropped over the 14th century. But these losses were also dependent on the starting state of the landscape: those with about 40% of tree cover were more stable but, in landscapes that were either too wooded or too open, diversity declines from abandoned farmlands were more extreme.

“Unlike in the present day – where crop monocultures are dominant – mixed agricultural systems were the norm over the majority of the last 2,000 years in Europe,” says Gordon. “The Black Death disrupted this by reducing human disturbance. The result was a less patchy landscape and an overall loss in plant diversity. Diversity only recovered when extensive farming returned.” From 1500 to 1850 CE, as populations recovered after the Black Death, so too did agricultural endeavors and economies, with biodiversity levels following suit.

“In the modern day, where monocultures and overgrazed landscapes predominate, agricultural practices are harmful for biodiversity,” writes Gordon. “But our work shows that this doesn’t need to be the case – human farming can boost biodiversity! But, the key is that it has to be the right kind: low intensity mosaics of semi-natural and natural elements coexisting in the same location.” To this day, man-made, diverse landscapes managed through low-intensity practices can be found in parts of Europe, making some of the most biodiverse spots. These High Nature Value farmlands support a mix of grazing and mixed farming, fostering biodiverse agro-ecosystems.

Over the years, conservation efforts have shifted towards methods that allow nature to regain control. For instance, rewilding introduces feral cattle, horses and other animals to sites in the hopes of creating patchy landscapes that enrich biodiversity. “Yet our work shows that rewilding and other approaches that seek to limit human influences are not the only solution. Traditional land management practices can also help generate these biodiversity gains, through a similar process of land disturbance,” adds Gordon. “This gives conservation another tool in the toolbox, where rewilding and other similar approaches are not feasible or desirable – in many places people don’t want large populations of feral cattle and wolves wandering around!”

Reference: Jonathan D. Gordon et al., Black Death Land Abandonment Drove European Diversity Losses, Ecology Letters (2026). DOI: https://doi.org/10.1111/ele.70325

Featured image credit: Dunk 🐝 via Flickr, CC BY 4.0