An intersection of climate, history and landscape use: 3000 years of central Italian environmental change

Abstract

Both climate change and historical events affect the environmental history of a place. Dis-entangling the two is challenging and requires independent reconstructions of climate and landscape change, as well as a thorough local historical narrative. Understanding the role climate and humans have played on shaping landscape is key to interpreting history and understanding the ecological trajectory of a region. Here I present a study which combines a climate reconstruction, a fossil pollen record of land cover change calibrated using a study of modern vegetation-pollen relationships, and a review of the archaeological and historical narrative in order to assess drivers of environmental change in central Italy. The climate and fossil pollen records are derived from a sediment core taken from Lake Ventina and cover the last 3000 years. δ18O and δ13C measurements on bulk carbonate produce a record which produces a semi-quantitative local climate reconstruction. Analysis of modern water samples confirm that the lake’s isotopic system today is sensitive to changes in water balance, which is driven by monthly and yearly trends in weather. The carbonate isotope record indicates a shift to more depleted δ18O and enriched δ13C between 750 and 950 AD, suggesting positive water balance and expanded wetland surrounding the lake. The record is compared to that from nearby Lake Lungo and the two match well from 750 AD to present, including periods of enriched δ18O from 1100 to 1400 AD and depleted δ18O from 1500 to 1800 AD, both of which conform well to regional patters of climate during those times. Analysis of fossil pollen from Lake Ventina reveals that from the beginning of the record in 1000 BC to 1400 AD, the area was characterized by a highly anthropogenic landscape dominated by fields and meadows with limited forest cover. This constrasts with findings from nearby Lake Lungo and highlights the spatial heterogeneity of landscape use in the past, with some sites being heavily utilized prior to and throughout the Roman period. Forest expanded dramatically after 1400 AD as a result of population decline resulting from the Black Death and a shift to cooler/wetter climate. Thirty modern pollen samples and paired surveys of the surrounding vegetation were used to characterize land cover-pollen relationships and aide in the interpretation of the fossil pollen record. A key finding is that cultivates and other anthropogenic indicators are underrepresented in the pollen record relative to their presence on the landscape, suggesting the pre-1400 AD landscape surrounding Lake Ventina must have been even more intensively utilized by humans than the pollen percentages indicate. Analysis of the modern pollen also indicates that there are not many modern analogs for pollen assemblages found in the Lake Ventina record, suggesting past landscapes were not similar to those of today. Overall this research represents a case study in long-term environmental history and demonstrates how records of climate and landscape change can be integrated with historical and archaeological records to greatly improve our understanding of ecological history.