A nature reserve on the border between Lazio and Umbria, a few kilometers from the city of Rieti. It is here that a team of researchers from INGV and the Universities of Nevada (USA) and Tuscia in Viterbo decided to study the influence of climate and social changes on the evolution of the central Apennines landscape.
The sediments taken from the bottoms of the Lungo and Ripasottile lakes, the last testimonies of that single large lake that once covered a large part of the Rieti plain, tell a story made up of civilizations which, century after century, have followed one another in the great journey of the history of man, handing down techniques and traditions that have forever marked the territory.
Therefore, not only climate change changes the landscape of our mountains, but also and above all social changes. We talked about it with Leonardo Sagnotti, Director of the INGV Environment Department and co-author of the article on historical ecology that reveals the transformations of the Apennine landscape published last year in Scientific Reports.
Let's start with a question that helps us understand: what is meant by "historical ecology"?
It all started a few years ago with a multidisciplinary research that analyzed sediment samples taken from the lakes of the Rieti basin (specifically, from the bottoms of Lago Lungo and Lago di Ripasottile). Some of the analyzes on these samples (called "carrots", ed) concerned the pollen content of the sediments, i.e. the quantity and type of pollen present within them. This type of investigation was carried out because pollens reflect ecological variations: it is in this sense that we speak, therefore, of "ecology".
Furthermore, since the sediments record the history of the basin, the pollen content was also able to reveal to us how the environment, and therefore the ecology, has changed over time. A part of the study, the one to which INGV specifically contributed, was in fact concerned with applying geophysical methods to date the sediments and provide a chronological framework for the changes in the environment: "historical ecology", to be precise.
What kind of changes have you identified in the Rieti basin?
One of the first things we were able to highlight was certainly how the level of the lakes has historically conditioned the alternation of different types of vegetation. We know that in the past centuries important variations in hydrology have been recorded in these areas: we have gone from moments in which there was a single large lake covering the entire area of the Piana Reatina, to others in which, as now, they have separate small ponds. Without forgetting the effects of the numerous attempts by man to reclaim the area by draining the plain.
Where does the inspiration behind this research come from?
It was a study funded by the National Science Foundation (NSF) which involved various research institutions: in addition to our Institute, the University of Nevada (USA) and the University of Tuscia also participated. We were contacted by the University of Tuscia as specialists in paleomagnetism and magnetic properties of rocks.
What was the role of INGV?
Our Paleomagnetism Laboratory was involved in the first place in the part of the study dedicated to the geophysical characterization and dating of the sediments taken from the bottoms of the two lakes. We formulated an age model of rocks by studying their magnetic properties and on the basis of recording past changes in the Earth's magnetic field.
The geophysical observations and the age model were then cross-referenced and compared with historical data relating to crops, pollen, knowledge of climatic variations over the last few centuries and calibrated secular variation curves of the earth's magnetic field in the European region during last three millennia.
What is the main finding of the study?
The study highlighted that the environmental variations in the Rieti basin were the result not only of the climatic variability of the last three millennia (such as, for example, the so-called "little glacial period" which occurred between the XNUMXth and XNUMXth centuries and the warm period between the tenth and thirteenth centuries), but also of the influence on the environment of the succession of human societies (from the Romans to the populations of the contemporary era, passing through the Ostrogoths, Lombards and Carolingians).
Each society has used the basin in a different way, exerting its influence on the territory. Furthermore, by applying the high-resolution age model to the sediments, another study published this year also made it possible to recognize the traces of four major seismic events that occurred in the area in the last 700-800 years. The effects of these earthquakes are visible both in the structure of the sediments and in the geochemical indicators of general hydrology, i.e. in the chemistry of the springs that feed the lakes. The major effect on the sedimentation, geochemistry and ecology of the basin occurred following the earthquake of 1349, when the Black Death was also raging in Europe, decimating its population. In the immediately following years, then, the sediments testify to an evident and rapid reforestation of the area connected to a marked depopulation of the territory.
One of the pieces of evidence that emerges from your research concerns the extent of the impact that social and cultural transformations have had on the territory of the central Apennines, comparable to that of climate change. Did you expect such a result?
Yes, let's say it was something that could in part be expected, of which we had confirmation. In the last three millennia the climatic variations have been all in all limited, certainly not as great as those of the Quaternary, characterized by the alternation of glacial and interglacial periods. Our study has shown how the effects of these small climatic variations are actually comparable to the effects linked to socio-cultural variations in land management, i.e. to the different types of forestry and agriculture, as well as water management, with the various attempts of drainage of the basin, and so on… In other words, even the historical eras, with their different societies and the relative different ways of managing the territory, have contributed decisively to modifying the landscape of the central Apennines.
Are you currently conducting other studies that go in this direction?
At the moment there are no other active searches on the same area and the same time interval. However, INGV continues to carry out and promote, in various parts of Italy and the world, various studies of sedimentary sequences to reconstruct the environmental and climatic variability of our planet.
Considering the impact that socio-cultural transformations have on the landscape, what kind of reflection is it possible to make on current events?
First of all, we can say with certainty that knowing the changes of the past helps us understand the dynamics of the present, and this applies not only to the historical aspects but also and above all to the natural ones.
During the Quaternary, i.e. over the last two million years, the climate varied significantly: we passed from glacial periods, in which practically all of northern Europe was buried under a blanket of ice, to rather interglacial periods brief, such as the one that covers the last 11 years (called "Holocene" in geological terminology), in which human civilization has developed. We know that major climate change is taking place today on a global and regional scale, which however seems to no longer follow natural rhythms as it is strongly influenced by human activities: in this sense, studying the dynamics of the past helps us to better understand the systems nature and their responses to environmental changes. This knowledge then allows us to formulate scenarios that are as realistic as possible about what could happen in the future.
In the picture: a view of the lakes of the Piana di Rieti. © George Rhone