ALBERT

Description: Using various archaeological and geoarchaeological operations, charcoal and waterlogged wood assemblages have been sampled in the marshy areas from the lower Dauphiné (Rhone valley, France). Their identification allows reconstructing the evolution of the woody vegetation in relation to climatohydrological changes and with human practices in the plain since the mid Holocene. It appears that humid-land forests have experienced a shift from ash formations (dominating during Pre- and Protohistory) toward alder formations between the Bronze Age and Roman Period. That vegetation change seems to be linked with pastoral practices in which fire is used as a clearing and regeneration tool. The intense pastoral use of the plain, together with the humidity of the soils when not artificially drained, may also have prevented the development of dense and mature forests. Finally, we show that beech, which is currently absent from the plain, probably grew in the marshlands during the past.

Description: This study presents a Holocene sediment budget for the Valdaine Region, located at the edge of the southern French Pre-Alps. Holocene colluvial and alluvial deposition are quantified based on existing and new field data. Average sediment thickness values were calculated for different landscape units, and available chronological data were used to make a time-differentiated sediment budget. Total Holocene colluvial deposition in the Valdaine (334 km 2 ) amounts 167 x 10 6 m 3 , while alluvial deposition in the Roubion and Jabron catchments (in total 610 km 2 , including their catchment upstream the Valdaine) amounts 177 x 10 6 m 3 . Especially, colluvial deposition is high (0.75 x 10 6 g/m 2 ) compared with other catchments. Three major deposition periods (8500–2000 bc , 700 bc – ad 800 and ad 1200–2000) and two periods of relative hillslope stability with local fluvial incision (2000–700 bc and ad 800–1200) set the framework for a time-differentiated sediment budget. Results show that depositional phases relate to intense land use and hillslope stability and fluvial incision to land abandonment. Catchment averaged colluvial deposition increases from 13 x 10 –6 m 3 /m 2 /yr for 8500–2000 bc to 355 x 10 –6 m 3 /m 2 /yr for ad 1200–2000, while alluvial deposition increases from 16 to 147 x 10 –6 m 3 /m 2 /yr between the same time periods. A relationship with climatic fluctuations was not found because of the limited temporal resolution of the sediment budget. The derived sediment cascade model shows how alluvial sediments change from fine (silt and clay) to coarse (sand and gravel) after ad 1200. This went along with the establishment of a braided river pattern, indicating that the main source of sediment shifted to the mountainous headwaters. Further research including fingerprinting and modeling would be necessary to further understand the sediment budget and to more accurately quantify the different source areas and the export from the catchment.

Description: Lac Moras is a small lake located on a low-elevation plateau in the upper Rhône Valley (304 m a.s.l.). The upper 5 m of accumulated sediment in the lake span 7500 years and offer a detailed record of environmental perturbations and land-use history at a local scale. A multiproxy analysis (pollen, charcoal and geochemical parameters) led to the establishment of four periods of landscape dynamics. The first evidence of human impacts was recorded during the Neolithic and Bronze Age (6000–2700 cal. BP). These impacts were temporary and most likely affected small areas. The second period, in the Iron Age/classical antiquity (2200–1900 cal. BP), appears to be a key period in which the intensification of anthropogenic pressure (primarily grazing with localised areas of cultivation) caused high-intensity erosion events and deeply affected soil stability. During the Middle Ages, wheat, rye and hemp cultures as well as tree farming (walnut, chestnut) were intensively developed. From 50 cal. BP (the 19th century) onward, crop cultivation declined and was gradually replaced by meadows and pastures. According to these transformations in agro-pastoral practices, the associated use of fire changed. Whereas fire was used intensively to clear wild areas from the Neolithic to the early Middle Ages, its use was restricted to cleaning agro-pastoral areas during the second part of the Middle Ages. These periods correspond to the different reconstructed types of land use. These changes correspond to population growth, the evolution of settlement patterns and the increase in agrarian productivity by technological advances. The present landscape is a result of this coupled agrarian and environmental history. It is notable that the first permanent alteration occurred as early as classical antiquity.