Mountain agro-ecosystems long-term trajectories in the North Western Alps

Past trajectories of alpine agro-ecosystems are legacies that we should consider in the context of current global changes. By integrating archaeology, history and multi-proxy palaeoenvironmental records including lake sediment DNA, we reconstructed the precise nature of agro-pastoral activities and their interactions with the landscape evolution (erosion and vegetation) in the Northwestern Alps, across an altitudinal gradient ranging from 880 and 2440 m a.s.l. We demonstrate that the origins of current vegetation cover in the “Alpages” date to the Mid to Late Bronze Age. However, at the lower limit of the subalpine belt and below this zone, the first significant plant cover changes date to a later period, from the Early to High Middle Ages. From the Bronze Age, we see also anthropogenic disturbances of the natural erosion cycle, especially on some sites in the subalpine belt. This erosion became generalized across all sites during the Roman period. Then, decreasing anthropogenic impacts on the erosion are recorded everywhere, which suggests the beginning of efficient soil management strategies, with protection of the soil resource. This important tipping point arose from the High to Late Middle Ages, when activities and practices are changing.