The Black Death: Why Abandoned Fields Reduced Biodiversity

The idea sounds appealing: if people disappear, nature can recover, forests can return, and animals and plants can reclaim space. Yet a major study into the effects of the 14th-century plague paints a very different picture. Where populations collapsed and fields were abandoned, biodiversity declined – recovering only once people and farming returned.

When plague struck: Europe in crisis

Between 1347 and 1353, what was probably the deadliest pandemic in European history swept across the continent. The plague, later known as the “Black Death”, is estimated to have killed between one-third and one-half of the population. In some towns, as many as 80 per cent of residents died. Rural areas suddenly lacked labourers, entire villages were deserted, and economic and food supply systems collapsed.

As people vanished, so did their cultivated land. Arable fields were no longer worked, farms were deserted and paths fell into disrepair. Forests, scrub and wild animals spread back across the open land. From a modern perspective, this may sound like a vast, unintended “rewilding experiment”: fewer people, more wilderness – therefore more life, more species and more nature. However, that is not what happened.

New analyses show that where people and arable land disappeared, plant diversity collapsed – wilderness did not replace diversity; it displaced it.

What 2,000 years of lake pollen reveal

To investigate this unexpected pattern, researchers examined ancient pollen records. Lake and peat sediments contain tiny pollen grains that can survive for millennia. They reveal which plants grew in a particular region at a given time.

For the new study, data from more than 100 such pollen archives across Europe were combined. The researchers reconstructed changes in plant biodiversity from the start of the Common Era to the early modern period – before, during and after the plague outbreak of the 14th century.

• Period 0–1300: gradual rise in plant diversity
• High Middle Ages: peak biodiversity
• From 1348: sharp decline lasting around 150 years
• Recovery: only with renewed agricultural use

The pattern is unmistakable. Plant diversity rose substantially from antiquity to the High Middle Ages. It increased during both the rise and decline of the Western Roman Empire, and continued to grow during the era of medieval farming. Biodiversity reached its highest point in the so-called High Middle Ages.

The arrival of plague reversed this trend. From the middle of the 14th century, plant diversity fell markedly and remained low for roughly 150 years. Only when population numbers began to rise again, new fields were established and arable land was cultivated more intensively did diversity slowly start to recover.

Where fields were abandoned, diversity declined

The findings become particularly revealing when pollen trends are compared with different forms of land use. The course of events was not identical everywhere. In some regions, arable land was abandoned completely, while elsewhere farming remained comparatively stable or even expanded.

The outcome was clear: plant diversity suffered its greatest decline where arable land was left fallow and land use dropped sharply. By contrast, the number of plant species increased in landscapes where agriculture remained stable or grew.

The greatest losses of biodiversity occurred precisely where human land use declined sharply and fields turned into uniform woodland or scrub.

This challenges a widespread assumption: reduced human influence does not automatically produce greater species richness. What matters is how landscapes are used, and how varied their structures and forms of management are.

Why traditional farming increased biodiversity

How could agricultural land use, of all things, increase biodiversity over centuries? The answer lies in the type of farming that prevailed at the time. From antiquity well into the Middle Ages, low-intensity mixed systems were dominant.

Rather than vast monocultures, the continent was shaped by a varied mosaic landscape:

• Small fields growing different crops
• Pastures and meadows under extensive grazing
• Woodland edges, hedgerows and small groups of trees in fields
• Fallow land, field margins and wet areas

This fragmented and varied landscape provided niches for numerous plant species. Plants requiring sunlight found suitable conditions along track edges and in arable fields, shade-tolerant species thrived in woodland, and specialist species occupied wetlands or nutrient-poor pasture. Regular yet relatively gentle disturbance – grazing, mowing and ploughing in small-scale rotation – allowed many less competitive species to persist over the long term.

When plague disrupted these forms of management, this very small-scale disturbance disappeared. Woodland expanded, scrub increased and open habitats vanished. The landscape became more uniform. Highly competitive species prevailed, while more sensitive specialists disappeared. Diversity therefore declined even though the area of “wild” nature grew.

What this means for modern conservation approaches

The findings call into question a common guiding principle in conservation policy: the idea that human influence should be reduced as far as possible in order to protect species. Across many European regions, large-scale wilderness projects have been regarded as an ideal for years. Yet in places where the landscape has been shaped by traditional farming for centuries, this approach can prove counterproductive.

European landscapes are often cultural landscapes shaped over time – if people are removed completely, the species that adapted to precisely this use often disappear.

Typical biodiversity hotspots today occur in areas with a long history of extensive management: heathland, traditional orchards, alpine pastures and small-scale arable-woodland mosaics. If these cultural landscapes are simply left to themselves, they become overgrown, and many species dependent on light and disturbance lose their habitat.

Examples from other world regions

The link between human land use and high biodiversity is not exclusively a European phenomenon. Historical practices have also produced highly varied ecosystems elsewhere:

• Forest gardens maintained by Indigenous communities on the north-west Pacific coast
• Satoyama landscapes in Japan, where rice terraces, woodland and streams alternate
• Traditionally structured land-use areas in island regions with tiered elevations

In all these cases, deliberate and often small-scale management creates species-rich habitats that would not exist in the same form without people. Modern, highly intensive agriculture destroys this diversity in many places, but historical experience shows that human presence can also support nature – when it takes the right form.

Lessons from the plague study for the future

The plague study delivers an uncomfortable but illuminating message: more woodland and fewer people do not automatically mean an ecological happy ending. The decisive factor is landscape structure. Diversity emerges where different uses, management practices and disturbance regimes exist alongside one another.

In practical terms, conservation should not focus solely on completely withdrawing land from use. It should also make greater use of traditional, low-intensity forms of land management. These include:

• Extensive grazing with low stocking densities
• Late-cut meadows with varied mowing dates
• Retaining hedgerows, field margins and small water bodies
• Small-scale arable systems rather than endless monocultures

Such measures increase heterogeneity across the landscape and provide space for a wide range of plant species – and consequently for insects, birds and other animal groups that depend on those plants.

Terms frequently misunderstood in the debate

Discussions often rely on terms that are easily confused. “Wilderness” refers to largely unmanaged land in which natural processes dominate. A “cultural landscape” is an area shaped and used by people over a long period. Both can support high biodiversity, but for different reasons. Wilderness primarily protects original species that are sensitive to disturbance. Cultural landscapes support many species adapted to human management.

The plague demonstrates what happens when a historically developed cultural landscape is suddenly left without management. Nature does return, but in a more uniform form. Species reliant on small-scale use disappear. For modern conservation policy, this means that failing to understand an area’s land-use history can quickly lead in the wrong direction.

Anyone making decisions today about afforestation, taking land out of production or creating large-scale refuges for nature should take this historical perspective into account. Sometimes biodiversity is protected not by people withdrawing, but by their conscious and restrained presence – at the right scale and using the right methods.