The science. When palynologists lend a helping hand to historians

Plague is an ecologically and epidemiologically complex disease transmitted in several ways. Its main reservoir is in rodents, and the disease-causing bacillus Yersinia pestis is transmitted to humans through direct contact with infected animals, flea bites, or airborne droplets.

A great plague devastated the Old Continent

In the middle of the fourteenthas well as century, between 1347 and 1352, the Great Plague destroyed, according to historians, from 30 to 50% of Europeans. In just five years, 50 million people would die from this pandemic. The consequences for European civilization are serious and long-term, as this disease has led to major socio-economic upheavals, including the transformation of religious, political, cultural and economic structures.

We used pollen data from 261 sites distributed
throughout Europe. Thus, it was in the corpus of 1634 samples that we looked for pollen.

Florence Mazier, palynologist and research fellow at CNRS

Until now, historians have argued with supporting texts that the effects of the plague would have had a devastating effect on demographics throughout the Old Continent. A recent study (1) based on pollen grains refutes this idea. “Pollinator data can be used to estimate demographic dynamics in the past, because human impact on the landscape in the pre-industrial period was directly dependent on the availability of labor in rural areas,” explains Florence Mazier, palynologist and researcher at CNRS. She participated in a study that has just been published by the Max Planck Institute’s paleoscience and history group led by Adam Izdebsky.

Palynology is the study of pollen grains and spores of plants stored in the sediments of lakes and swamps. But what could be its connection with the plague? “The identification of pollen grains makes it possible to trace the history of land cover and, through landscape changes, to understand the demographic consequences of the Black Death,” the researcher continues.

Quote IconThe identification of pollen grains makes it possible to trace the history of land cover and to understand through landscape changes the demographic consequences of the Black Death.Florence Mazier, palynologist

In the publication, the authors identified regions characterized by shrinking, stable or expanding agricultural landscapes in Europe. To do this, scientists dug not in sedimentary layers, but in databases. The published study is indeed one of the first of its kind to use big data in palynology. “We used pollen data from 261 sites across Europe. So we were looking for pollen in a corpus of 1634 samples,” says Florence Mazier.

Regional differences

The researchers actually focused their analysis on four groups of plants: croplands (which are indicative of an agricultural labor force), those that reflect pastures (areas requiring less labor), and those that characterize “rapid secondary forest successions.” . “, i.e. shrubs and trees growing five to ten years after the abandonment of the land, and those of the “slow secondary forest successions”, which testify to an even more ancient abandonment.

The results are not subject to appeal! During the Black Death period, pollen revealed regional disparities in farming intensity across Europe. Thus, the researchers identified regions characterized by a sharp decline in agricultural technology, for example, in Scandinavia, France or central Italy. Conversely, some regions of Central Europe, Ireland or Spain show signs of continuity and sometimes even agrarian growth.

So what’s new is that pollen studies show that Black Death mortality was much more spatially heterogeneous than historians think. “The fact that the pandemic has been extremely devastating in some regions, but not all, falsifies the common practice in Black Death studies of predicting the experience of one region based on another,” the researchers conclude in their publication. Nationwide mortality results need to be reconstructed using more local sources than pollen, the evidence for this may help to know…

(1) “Palaeoenvironmental evidence points to changes in land use in Europe associated with spatial heterogeneity in mortality during the Black Death pandemic”, Nature Ecology and Evolution, 2022.

Point of view

“The plague hit Europe unevenly”

Florence Mazier, palynologist in charge of research at CNRS.

How was the choice made from 261 sites?

We have been limited by the presence of pollen patches that have already been dated, analyzed, published and available in pollen databases or directly from researchers. These sites also need to have good temporal resolution in order to inform about the period of the plague in the middle of the fourteenth well as century. In addition, we also had to take into account the regions for which multiple sites were available in order for our results to be well representative. For future experiments, core/sampling will be conducted at well-defined locations to cross-reference historical and high-temporal resolution pollen data in the same areas.

Why is current research on the plague not accurate?

One of the goals of this study was to show that current studies of the plague, which are based on the analysis of documents, texts or stories that speak of a pandemic in large cities, are incomplete. In cities, mortality reached 25 to 50% due to the concentration of the population or the unsanitary conditions that existed at that time. The bacillus is transmitted very easily. The problem is that this image is necessarily biased because the population in Europe is largely rural, over 70% in the 14th well as century. So we had to look for new sources of data. I had to plug holes in history, because there are few texts about the rural environment. Our research suggests that the plague hit Europe unevenly.

What do historians think of your work?

They are very surprised and this makes them reconsider certain information. But our research shows, first of all, that when we cross disciplines, we learn much more. This is a great call for cooperation between the humanities and the natural sciences. In palynology, we can also see the consequences of wars, revolutions that lead to changes in land use, and therefore to changes in vegetation cover. We’re looking at the effects of desolation over the past two hundred years in the mountains, we’re seeing what’s happening to the vegetation in terms of plant diversity. Palynology is a cross-cutting science that gives us the opportunity to work with historians, botanists, ecologists and even climatologists…

Interview with J.B.

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