Black Death's abandoned farms cut plant biodiversity 40%, then a 150-year comeback

When the Black Death swept through Europe in the 14th century, it took out more than a third of the population. It also, new research shows, knocked plant biodiversity down in the farmlands that were suddenly abandoned. In those landscapes where agricultural production fell, plant biodiversity dropped by around 40%, according to a study published March 4 in the journal Ecology Letters. The lead author is Jonathan Gordon, a paleoecologist at the Leverhulme Centre for Anthropocene Biodiversity at the University of York.

The surprise is what happened next. About 150 years later, as Europe's population recovered and people began disturbing the land again, biodiversity climbed back to slightly above where it had been before the plague. Gordon and his colleagues reached these conclusions by comparing more than 100 European pollen records, covering about 4,600 samples, from sites spanning the lowlands of France, the uplands of southwest United Kingdom, and the Swiss Alps. Pollen from cereal grains such as wheat, barley, and rye tracks historic agricultural activity, letting researchers separate places where farming intensified, declined, or disappeared.

The finding inverts a common assumption. Many people assume pre-human landscapes were stable and pristine, and human activity always produces net loss of species. But paleoecologists have long known it's more complicated, says Erle Ellis, an agroecologist at the University of Maryland, Baltimore County, who was not involved in the research. Medieval farmland was a mosaic: small fields interlaced with old bits of woodland, heaths, ponds, and secondary forest. That patchwork created more habitats for more plant species, a pattern that disappeared when the land was left alone.

Patrick Roberts, director of the Department of Coevolution of Land Use and Urbanisation at the Max Planck Institute of Geoanthropology, who was also not involved, points to the contrast with modern practice. Rather than the monoculture, plantations, or uniform changes to landscapes seen in the 20th and 21st centuries, emphasis was placed on maintaining mosaics, he said. That distinction matters because modern farming typically grows a single crop over large areas, a system that lowers biodiversity. The study suggests that abandoning land altogether is not automatically good for nature, and that the way humans manage land can sometimes enhance diversity.

The modern consequences are measurable. Research cited in the study suggests global biodiversity declined by as much as 11% during the 20th century, with land-use changes, pollution, and climate change as major drivers. Monoculture is one of those land-use changes. For a food system under pressure to feed a growing population while halting nature loss, the Black Death-era results offer a counterintuitive insight: simply removing people and farmland did not restore biodiversity; it reduced it. Deliberate, mixed management seemed to do a better job.

Gordon cautions there is more to understand. Diversity is not just the number of plant types, but what those types do functionally. Functional diversity is super important for how ecosystems adapt to climate change and how resilient they are, which is something we need for future-proofing our agricultural system, he said. For executives in agriculture, land management, and food supply chains, that raises a strategic question: are current sustainability programs measuring the right thing? Counting species alone may miss whether the ecosystem can withstand shocks, whether that is drought, pests, or price swings.

For boards reviewing ESG and biodiversity commitments, the study is a reminder that context matters. Medieval mosaics worked because they mixed production and natural features at small scale. The challenge for modern operators is scaling that mix without losing efficiency. But the payoff, as Gordon frames it, is resilience in the face of climate change, and that is a competitive advantage. The lesson of the Black Death is not that humans should vanish from the landscape, but that how we show up in it determines what survives.