Evolution of Land use at lake St Point (Jura Mountains) since the neolithic Period / Emilie Gauthier

Evolution of Land use at lake St Point (Jura Mountains) since the neolithic Period : palynological and sedimentological analyses. Emilie GAUTHIER. In "La construction des territoires montagnards : exploitation des ressources et mobilité des pratiques, 2ème International Workshop on archaeology of european mountain landscape, organisé par les Laboratoires GEODE et TRACES (Toulouse) et le Centre d'Archéologie Préhistorique du Rhône aux Alpes (Valence, France). Université Toulouse II-Le Mirail, 8-11 octobre 2009. [Première journée.]

Lake St Point (850 m ASL.) is located in the central part of Jura Mountains. The vegetation surrounding the lake is represented by wood pastures. Pasture woodland is a very ancient form of land use, characterized by a mosaic landscape, from the open pasture to the closed forest. In the context of human impact on vegetation, the aim of this study is to investigate chronology and details of the transition between the original ecosystems to the sylvopastoral ecosystem.The deepest part of Lake St Point was cored from a floating platform. Chronology of the sequence is based on 24 AMS radiocarbon dates spread over the upper 7 m of the core. Concerning the recent period, 137Cs measurements were processed on the 20 upper centimeters of the sequence. The first results confirm the high quality of the deep lacustrine records and their scientific interest. The sediment succession collected in Lake St Point reveals a stratigraphically continuous profile spanning the entire Holocene period, and showing particular sensitivity to Human impact on vegetation. Pollen analysis reveals the first human impact as soon as the early Neolithic period, around 5300 cal. BC. Then, first farmers disappear until 4000 cal. BC. From this period to the end of Bronze Age, a particular land use takes place. Distinct pulses of forest clearance as a result of human activity can be observed. Among anthropogenic indicators, peaks of Cerealia type are followed by the increase of open landscape herbs. In a third phase, shrubs and light demanding trees (Juniperus, Acer…) develop in the clearance. Sedimentological analyses show that silicates and detrital carbonate fractions progressively increased, due to the erosion of soil. From the end of Bronze Age to the end of Iron Age, both Cerealia type and plants of open landscape curves increase and decrease together. This different signal suggests a new type of land use, with permanent fields. The Hallstatt period is characterized by regular human impacts while La Tène period correspond to a decline of agriculture. However, human pressure remains perceptible with regular clearance in the Fagus and Abies forest. Silicates content still increased while detrital carbonates input became steady due to a change in pedogenetic processes affecting thecatchment. he two last millennia have recorded the most important human impact: large"scale deforestation, especially during the Middle Ages, altered the vegetation cover drastically. Grassland became used more intensively and during the modern period, silicates and detrital carbonate decreased, probably due to wood pastures development.