Periodic Reporting for period 1 - PALEO-AGRI (agroPastoral Activities and effects on Landscapes and ErOsion dynAmics in the alps:a new insight from Geological appRoaches and lake sedIment DNA)
Reporting period: 2015-06-01 to 2017-05-31
Despite the increasing popularity of sediment DNA studies, almost nothing is known about the taphonomic processes (DNA source, transfer and deposit), which might affect and bias DNA records - WP1 of PALEO-AGRI aimed to address this issue. WP2 focused on the study of archaeological sites in the Ecrins Massif, where appropriate lakes for DNA analyses are missing. The goals of this WP were: 1) to provide information about the past use of the structures that yield very little material culture due to poor preservation conditions, and 2) to assess the legacy of past human activities on the current ecosystem. WP3 focussed on the reconstruction of the spatiotemporal dynamic of agro-pastoral activities and their effects on soil erosion and plant cover.
WP1: Our data suggest that extracellular DNA from the catchment area is more efficiently archived in lakes with high detrital inputs. The source of eroded material is also important: the erosion of deep soil horizons and inputs of glacial materials trigger dilutions of DNA quantity archived in sediments. Moreover, specific chemical conditions affecting lake sediment DNA preservation and/or analysis success can explain the non- or low-detection of DNA. Factors that influence the DNA record in lake sediments can change over time and thus significantly affect the quality of reconstructions of plant cover and livestock farming/pasturing histories.
WP2: Significant lead concentrations were detected in all medieval structures as well as in the modern enclosure, which suggests these sites were associated with mining activities. Interestingly, the beginning of this period corresponds to the most significant development of pastoral activities in the area. To understand the dynamic of pastoral activities over time, we should thus also consider the history of the development of mining activities in high-altitude areas and their economic importance.
The disturbance of the environment directly related to human activities (via the archaeological structures and the immediate environment) can still be detected through the soil geochemical signature and plant communities at least several centuries after disturbance.
WP3: In the Northern lakes (Anterne, La Thuile), the earliest pastoral activities might have developed during the Late Neolithic. However, our indications remain debatable and need to be reconsidered in light of new analyses, which are in progress. During the Late Iron Age and the Roman period, pastoral activities increased substantially, with sheep and cattle at high altitude. This intensive use of pastures led to soil erosion. Another phase of intensive grazing activity took place during the Medieval Period, from 1000 AD. However, there is no/little erosion, which might reflect a new land-use management strategy. Especially at the mid-altitude site (La Thuile), the development of fruit trees (Pyrus sp., Juglandaceae sp. and Prunus sp.) might have limited soil loss. From the 13th-14th centuries, it is apparent that cattle become more important than sheep, which might indicate an alpine economic “revolution”. Between 1200 and 1450 AD, the detection of Vitaceae sp. suggests vine culture. The decline of this culture coincides with a significant decrease in temperature during the Little Ice Age; a possible response by the Alpine community to climate change. To the south (Lake Muzelle), pastoral activities seem to develop later. In fact, over the last 1600 years, plants often associated to pastoral activities (Rumex sp. and Mentheae sp.) are only sparsely detected from 1500 AD and continuously from 1800 AD. This different temporal pattern highlights the complex history of agrarian activities in the French Alps.