A new interdisciplinary study has revealed that medieval communities around Lake Constance dramatically increased biodiversity through their farming practices, land management, and expanding economic networks. Drawing on fossil pollen, archaeobotanical evidence, and rich monastic archives, researchers show that the Lake Constance region — once a core territory of the Carolingian Empire — experienced a 4,000-year peak in plant diversity around the year 1000. Rather than degrading the landscape, early medieval societies created an ecological mosaic that supported a remarkable expansion of plant life.
The findings, published in the Proceedings of the National Academy of Sciences, add historical depth to modern debates about conservation. They also demonstrate that human activity does not inevitably lead to biodiversity loss and that medieval agricultural systems offer lessons for sustainable land management today.
“Human communities can support biodiverse landscapes, and have done so for long periods of time in the past,” explains Adam Izdebski of the Max Planck Institute of Geoanthropology. The Lake Constance case, he says, represents “a success story in human–environment interactions.”
A Measured Surge in Medieval Biodiversity
Lake sediment core from the greater Lake Constance region, split lengthwise to reveal sedimentation layers. From cores like this, fossil pollen is extracted and taxonomically identified to reconstruct centuries of regional plant diversity change. Image credit Sara Saeidi (Deutsche Forschungsgemeinschaft (DFG) Project number 443614159)
Using pollen data from six lake sediment cores, researchers reconstructed 4,000 years of plant diversity in the western Lake Constance region. Their analysis shows a 48% rise in plant richness between 500 and 1000 CE, during which the number of estimated plant taxa increased from around 27 to 40. Shannon’s Diversity Index — a standard measure of ecological diversity — increased by 23%, which corresponds to a 65% rise in the effective number of taxa.
This transformation, the study argues, was not simply a function of climate. Instead, it emerged from new agricultural practices, population growth, and the development of an extensive network of trade and land management linked to the Monastery of St. Gall.
Notably, the study finds that plant diversity peaked around 1000 CE and then declined sharply around 1350 — coinciding with the arrival of the Black Death in the region. Pollen records show a dramatic drop in diversity during this period, mirroring documentary evidence of widespread depopulation and agricultural contraction. Diversity rose again after 1450, though not to the even, mosaic-like landscape structure of the earlier medieval period.
How Medieval Agriculture Created a Biodiversity “Patchwork”
Modern view of the landscape that experienced a large, agriculture-driven expansion of regional plant diversity during the early medieval period. Taken at Hohentwiel Castle overlooking the countryside near the western shores of Lake Constance. Image credit: Adam Spitzig
The rise in biodiversity was largely driven by the expansion of upland herb and grass taxa, including crop weeds, plants associated with pastures and fallow fields, and ruderals — species that thrive in disturbed soils. Between 500 and 1000 CE, the number of herb and grass taxa nearly doubled. These plants flourished as medieval communities converted woodlands into farmland, drained wetlands, expanded grazing areas, and established new settlements.
This landscape resembled what ecologists call an intermediate-disturbance system: neither untouched wilderness nor intensively managed monoculture, but a mosaic of forests, meadows, fields, gardens, and semi-wild spaces. Such patchworks are now understood to support high biodiversity because they create numerous ecological niches and transitional zones.
Archaeobotanical evidence from hundreds of sites in southwestern Germany confirms that wild plant species — especially crop weeds, grassland plants, and ruderals — reached historically unprecedented levels between the Roman and medieval periods. These findings closely mirror the pollen data and show that the trend was regional, not limited to the Lake Constance shoreline.
The Role of St. Gall and the Carolingian “Agricultural Revolution”
Charter from the Abbey Archives of St. Gall. Dated March 9th, 736. Describes the donation of property in Eigeltingen and Neuhausen, near Lake Constance. Archived documents like this reveal the social, economic, and agricultural practices prevailing in the Lake Constance region during the early medieval period. Image credit; St. Gallen, Stiftsarchiv, IV 345 (Private charter)
One of the most striking aspects of the study is the importance of the Monastery of St. Gall, whose exceptionally rich archives allow researchers to connect environmental change to specific agricultural practices. Founded in the early eighth century, St. Gall accumulated thousands of properties across what is now Germany, Switzerland, and Austria. More than 850 original or contemporary copies of legal documents survive, offering detailed evidence for early medieval land use.
These records show that the region underwent a rapid agricultural transformation beginning in the eighth century. Documents describe:
The early adoption of the three-field system as early as 763 CE
Widespread cultivation of rye and oats, cereals well suited to harsh conditions
The introduction of iron ploughshares
Expansion of settlement networks, including new roads and village foundations
Cultivation of marginal soils, which increased the diversity of managed landscapes
These innovations increased yields and allowed communities to support larger populations. They also created more varied ecological settings, contributing directly to rising biodiversity.
Trade Networks and the Arrival of New Plant Species
A particularly important new insight from the study is the immigration of plant species from southern Europe. Archaeobotanical remains show that many crop weeds and grassland plants that became common around Lake Constance between 800 and 1000 CE originally came from Mediterranean or sub-Mediterranean regions.
The researchers argue that this influx was facilitated by St. Gall’s expanding economic networks. The monastery managed landholdings stretching from Allgäu to Alsace and maintained trading connections reaching as far as Lombardy and Tuscany. Through these channels, seeds travelled — intentionally or not — and established themselves in the increasingly open agricultural landscape.
This is one of the clearest examples in medieval Europe of how trade and cultural exchange directly reshaped local ecosystems.
The Black Death and the End of the Diversity Optimum
Around 1350, the region’s biodiversity collapsed. The study connects this directly to population loss from plague outbreaks documented in both urban centres like Constance and rural monasteries such as Zwiefalten. Some areas lost between 30% and 50% of their population.
With fewer people to maintain fields, orchards, and managed woodlands, large areas reverted to less varied ecological forms. The landscape became more homogeneous, reversing centuries of biodiversity growth.
Even when population levels recovered after 1500, plant communities did not return to the same even distribution. Instead, the early modern period introduced proto-industrial agriculture, including flax monocropping for linen production, which further reduced ecological variety.
The authors argue that the medieval Lake Constance region demonstrates how small-scale, diversified agriculture can maintain — and even increase — biodiversity while supporting robust food production. This challenges modern assumptions about the relationship between human activity and ecological decline.
“This study offers lessons for policy makers and conservationists,” adds Adam Spitzig of Stanford University. “Our data suggest that High Nature Value (HNV) farming systems and intermediate-disturbance, agro-ecological mosaics can effectively enhance plant diversity while simultaneously sustaining food production.”
The article, “Cultural innovation can increase and maintain biodiversity:A case study from medieval Europe,” by Adam Spitziga, Manfred Rösch, Jessie Woodbridge, Martin Bauch, Piotr Guzowski, Peter Erhart, Ralph Fyfe, Elena Marinova and Adam Izdebski, appears in Proceedings of the National Academy of Sciences. Click here to read it.
Top Image: BnF. Département des Manuscrits. Latin 6862 fol. 18v
A new interdisciplinary study has revealed that medieval communities around Lake Constance dramatically increased biodiversity through their farming practices, land management, and expanding economic networks. Drawing on fossil pollen, archaeobotanical evidence, and rich monastic archives, researchers show that the Lake Constance region — once a core territory of the Carolingian Empire — experienced a 4,000-year peak in plant diversity around the year 1000. Rather than degrading the landscape, early medieval societies created an ecological mosaic that supported a remarkable expansion of plant life.
The findings, published in the Proceedings of the National Academy of Sciences, add historical depth to modern debates about conservation. They also demonstrate that human activity does not inevitably lead to biodiversity loss and that medieval agricultural systems offer lessons for sustainable land management today.
“Human communities can support biodiverse landscapes, and have done so for long periods of time in the past,” explains Adam Izdebski of the Max Planck Institute of Geoanthropology. The Lake Constance case, he says, represents “a success story in human–environment interactions.”
A Measured Surge in Medieval Biodiversity
Using pollen data from six lake sediment cores, researchers reconstructed 4,000 years of plant diversity in the western Lake Constance region. Their analysis shows a 48% rise in plant richness between 500 and 1000 CE, during which the number of estimated plant taxa increased from around 27 to 40. Shannon’s Diversity Index — a standard measure of ecological diversity — increased by 23%, which corresponds to a 65% rise in the effective number of taxa.
This transformation, the study argues, was not simply a function of climate. Instead, it emerged from new agricultural practices, population growth, and the development of an extensive network of trade and land management linked to the Monastery of St. Gall.
Notably, the study finds that plant diversity peaked around 1000 CE and then declined sharply around 1350 — coinciding with the arrival of the Black Death in the region. Pollen records show a dramatic drop in diversity during this period, mirroring documentary evidence of widespread depopulation and agricultural contraction. Diversity rose again after 1450, though not to the even, mosaic-like landscape structure of the earlier medieval period.
How Medieval Agriculture Created a Biodiversity “Patchwork”
The rise in biodiversity was largely driven by the expansion of upland herb and grass taxa, including crop weeds, plants associated with pastures and fallow fields, and ruderals — species that thrive in disturbed soils. Between 500 and 1000 CE, the number of herb and grass taxa nearly doubled. These plants flourished as medieval communities converted woodlands into farmland, drained wetlands, expanded grazing areas, and established new settlements.
This landscape resembled what ecologists call an intermediate-disturbance system: neither untouched wilderness nor intensively managed monoculture, but a mosaic of forests, meadows, fields, gardens, and semi-wild spaces. Such patchworks are now understood to support high biodiversity because they create numerous ecological niches and transitional zones.
Archaeobotanical evidence from hundreds of sites in southwestern Germany confirms that wild plant species — especially crop weeds, grassland plants, and ruderals — reached historically unprecedented levels between the Roman and medieval periods. These findings closely mirror the pollen data and show that the trend was regional, not limited to the Lake Constance shoreline.
The Role of St. Gall and the Carolingian “Agricultural Revolution”
One of the most striking aspects of the study is the importance of the Monastery of St. Gall, whose exceptionally rich archives allow researchers to connect environmental change to specific agricultural practices. Founded in the early eighth century, St. Gall accumulated thousands of properties across what is now Germany, Switzerland, and Austria. More than 850 original or contemporary copies of legal documents survive, offering detailed evidence for early medieval land use.
These records show that the region underwent a rapid agricultural transformation beginning in the eighth century. Documents describe:
These innovations increased yields and allowed communities to support larger populations. They also created more varied ecological settings, contributing directly to rising biodiversity.
Trade Networks and the Arrival of New Plant Species
A particularly important new insight from the study is the immigration of plant species from southern Europe. Archaeobotanical remains show that many crop weeds and grassland plants that became common around Lake Constance between 800 and 1000 CE originally came from Mediterranean or sub-Mediterranean regions.
The researchers argue that this influx was facilitated by St. Gall’s expanding economic networks. The monastery managed landholdings stretching from Allgäu to Alsace and maintained trading connections reaching as far as Lombardy and Tuscany. Through these channels, seeds travelled — intentionally or not — and established themselves in the increasingly open agricultural landscape.
This is one of the clearest examples in medieval Europe of how trade and cultural exchange directly reshaped local ecosystems.
The Black Death and the End of the Diversity Optimum
Around 1350, the region’s biodiversity collapsed. The study connects this directly to population loss from plague outbreaks documented in both urban centres like Constance and rural monasteries such as Zwiefalten. Some areas lost between 30% and 50% of their population.
With fewer people to maintain fields, orchards, and managed woodlands, large areas reverted to less varied ecological forms. The landscape became more homogeneous, reversing centuries of biodiversity growth.
Even when population levels recovered after 1500, plant communities did not return to the same even distribution. Instead, the early modern period introduced proto-industrial agriculture, including flax monocropping for linen production, which further reduced ecological variety.
Lessons from the Medieval Past
The authors argue that the medieval Lake Constance region demonstrates how small-scale, diversified agriculture can maintain — and even increase — biodiversity while supporting robust food production. This challenges modern assumptions about the relationship between human activity and ecological decline.
“This study offers lessons for policy makers and conservationists,” adds Adam Spitzig of Stanford University. “Our data suggest that High Nature Value (HNV) farming systems and intermediate-disturbance, agro-ecological mosaics can effectively enhance plant diversity while simultaneously sustaining food production.”
The article, “Cultural innovation can increase and maintain biodiversity:A case study from medieval Europe,” by Adam Spitziga, Manfred Rösch, Jessie Woodbridge, Martin Bauch, Piotr Guzowski, Peter Erhart, Ralph Fyfe, Elena Marinova and Adam Izdebski, appears in Proceedings of the National Academy of Sciences. Click here to read it.
Top Image: BnF. Département des Manuscrits. Latin 6862 fol. 18v
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