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Medieval Farms Were a Boon for Biodiversity, Research Finds

In Europe, the diversity of plants was greatest in the years before the Black Death, at a time when small farms and pastures existed alongside grasslands and forests, new research reveals. The findings show how, under the right conditions, farms can be a boon to nature.

Researchers focused on the lands around Lake Constance, which lies at the borders of Germany, Austria, and Switzerland, tracking changes in the local flora from 2000 B.C. until the present day. For the study, they gathered data from thousands of fossilized pollen grains, plant remains recovered from hundreds of archaeological sites, and reams of legal records kept at the nearby Monastery of St. Gall, among other sources.

Researchers found that the diversity of plants rose steadily from 500 A.D. until around the year 1000 as farms expanded and trade grew. Over time, farmers created a patchwork of fields, pastures, and forests that supported a greater array of plants than either the closed forests that came before or the industrial farms that would follow.

Around Lake Constance, researchers discovered not just greater varieties of crops, but weeds, grasses, and even some shrubs and trees. The process was additive, said lead author Adam Spitzig, a PhD candidate at Stanford University. Old plants persisted while new plants suited to open or disturbed landscapes took root.

When the Black Death came to Lake Constance around 1350, it decimated the population, wiping out half the people in some villages. Farms collapsed, and the diversity of plants diminished. As the region recovered, diversity rebounded, but it never returned to its previous heights. The growth of linen-making meant that farms were increasingly devoted to growing flax and raising cows, whose milk was used in bleaching.

The study, recently published in Proceedings of the National Academy of Sciences, follows on prior research showing how the growth of farming in medieval Europe led to a “honeymoon” period, where small farms boosted the diversity of plants. The findings were further corroborated in a study published this month in Ecology Letters, which found that biodiversity declined during the Black Death, even as large swaths of land rewilded.

“The broader lesson is that, in modern conservation, the choice isn’t simply between farming and biodiversity,” Spitzig told Yale E360. Small, diversified farms “can boost and sustain biodiversity while supporting food production.”