An approach to Holocene vegetation history in the middle Rhone valley (France): anthracological data from the « TGV-Méditerranée » excavations

The construction of the « TGV-Méditerranée » railway, connecting Paris to the Mediterranean, has allowed large-scale rescue excavations to take place through out the middle Rhone valley. These provided wood charcoal fragments not only from archaeological settlements but also from off-site sequences. Their analysis has allowed us to propose a high resolution reconstruction of the vegetation history, that has proved to be quite different from the pattern previously admitted for the karstic peripheral hills. An early colonisation of the area by deciduous oak is attested during the Late Glacial interstades. The Preboreal and Boreal are marked by high proportions of pine before deciduous oak formations became definitively dominant. If the middle Neolithic experiences a specialised management of the landscape by agro-pastoral populations, the vegetation that settles at the transition with the Bronze Age seems to be more influenced by a climatic change towards more humid conditions. The early Bronze Age is marked by a fall-off in agricultural activities together with a probable climate cooling. On the contrary, the final Bronze Age and even more the Iron Age are periods of vegetation diversity due to the increasing human impact on the landscape, while the climatic context gets dryer. The Classical period is a time of strong anthropisation of the landscapes favouring vegetation biodiversity. During the early Middle Ages, deciduous oak forests partly regenerate thanks to a short decrease of agricultural activities. During the late Middle Ages, cooling tracers tend to decrease while anthropogenic markers tend to increase. The modern period seems to be marked by a loss of biodiversity, following a fall-off in agricultural activities. Most of the lost taxa reappear during the sub-contemporary period, maybe because of a climatic improvement and of a reorganisation of agricultural lands towards vine monoculture, beneficial to “garrigue” species