Analyse spatiale et typologie des petites vallées bas-normandes

International audienceAlthough the landscapes of the valleys are original and subject to increasing stakes, they still are not studied very much, because landscape studies are often done to encompassing territorial scales; the studies disregard the specificity of those landscapes. This analysis is based upon the setting up of a typology of landscape of the valleys of the northwest France and the working-out of prospective patterns. Its aim is to help define the policies of "integrated management" which are adapted to those territories. This reasoning is carried out via the realisation of a diagnosis of present landscapes of small valleys following a reasoning which can be reproduced. At first we set up a morphological typology of valleys at a regional scale. After the limits of the valleys have been made explicit (the slopes and the bottoms of the valleys), homogeneous sections are made out. This approach shows the importance of these areas in the structure to the regional landscape and it puts forward new thoughts about the layout of their land use.Bien qu'originaux et soumis à des enjeux croissants, les paysages de vallées demeurent peu étudiés en tant que tels car les études paysagères sont souvent situées à des échelles territoriales englobantes qui négligent leur spécificité. Appuyée sur la mise en place d'une typologie des paysages de vallées représentatifs du Nord Ouest de la France et la construction de scénarii prospectifs, cette réflexion vise à contribuer à la définition de politiques de gestion intégrée adaptées à ces territoires. Cette démarche est menée à travers la réalisation d'un diagnostic de l'état actuel des paysages des petites vallées selon une démarche reproductible Il permet de mettre en place une typologie morphologique des vallées à l'échelle du territoire régional. Après avoir extrait les limites de vallées (versants et fond de vallée) des tronçons homogènes sont distingués. Cette approche révèle l'importance de ces espaces dans la structuration du paysage régional et suggère de nouvelles réflexions sur l'organisation de leurs modes d'occupation du sol

Natural vs anthropogenic streams in Europe: History, ecology and implications for restoration, river-rewilding and riverine ecosystem services

This is the author accepted manuscript. The final version is available from Elsevier via the DOI in this recordIn Europe and North America the prevailing model of “natural” lowland streams is incised-meandering channels with silt-clay floodplains, and this is the typical template for stream restoration. Using both published and new unpublished geological and historical data from Europe we critically review this model, show how it is inappropriate for the European context, and examine the implications for carbon sequestration and Riverine Ecosystem Services (RES) including river rewilding. This paper brings together for the first time, all the pertinent strands of evidence we now have on the long-term trajectories of floodplain system from sediment-based dating to sedaDNA. Floodplain chronostratigraphy shows that early Holocene streams were predominantly multi-channel (anabranching) systems, often choked with vegetation and relatively rarely single-channel actively meandering systems. Floodplains were either non-existent or limited to adjacent organic-filled palaeochannels, spring/valley mires and flushes. This applied to many, if not most, small to medium rivers but also major sections of the larger rivers such as the Thames, Seine, Rhône, Lower Rhine, Vistula and Danube. As shown by radiocarbon and optically stimulated luminescence (OSL) dating during the mid-late Holocene c. 4–2 ka BP, overbank silt-clay deposition transformed European floodplains, covering former wetlands and silting-up secondary channels. This was followed by direct intervention in the Medieval period incorporating weir and mill-based systems – part of a deep engagement with rivers and floodplains which is even reflected in river and floodplain settlement place names. The final transformation was the “industrialisation of channels” through hard-engineering – part of the Anthropocene great acceleration. The primary causative factor in transforming pristine floodplains was accelerated soil erosion caused by deforestation and arable farming, but with effective sediment delivery also reflecting climatic fluctuations. Later floodplain modifications built on these transformed floodplain topographies. So, unlike North America where channel-floodplain transformation was rapid, the transformation of European streams occurred over a much longer time-period with considerable spatial diversity regarding timing and kind of modification. This has had implications for the evolution of RES including reduced carbon sequestration over the past millennia. Due to the multi-faceted combination of catchment controls, ecological change and cultural legacy, it is impractical, if not impossible, to identify an originally natural condition and thus restore European rivers to their pre-transformation state (naturalisation). Nevertheless, attempts to restore to historical (pre-industrial) states allowing for natural floodplain processes can have both ecological and carbon offset benefits, as well as additional abiotic benefits such as flood attenuation and water quality improvements. This includes rewilding using beaver reintroduction which has overall positive benefits on river corridor ecology. New developments, particularly biomolecular methods offer the potential of unifying modern ecological monitoring with the reconstruction of past ecosystems and their trajectories. The sustainable restoration of rivers and floodplains designed to maximise desirable RES and natural capital must be predicated on the awareness that Anthropocene rivers are still largely imprisoned in the banks of their history and this requires acceptance of an increased complexity for the achievement and maintenance of desirable restoration goals.OSL dating from the Severn-Wye Basin was undertaken at the Geochronology Laboratories, University of Gloucestershire under grants from the EU Leader+ Programme (administered by English Heritage) and the Leverhulme Flood and Flow Project (RPG-2016-004)

The emergence of pottery in Africa during the tenth millennium cal BC: new evidence from Ounjougou (Mali)

New excavations in ravines at Ounjougou in Mali have brought to light a lithic and ceramic assemblage that dates from before 9400 cal BC. The authors show that this first use of pottery coincides with a warm wet period in the Sahara. As in East Asia, where very early ceramics are also known, the pottery and small bifacial arrowheads were the components of a new subsistence strategy exploiting an ecology associated with abundant wild grasses. In Africa, however, the seeds were probably boiled (then as now) rather than made into brea

The emergence of pottery in Africa during the tenth millennium cal BC: new evidence from Ounjougou (Mali)

New excavations in ravines at Ounjougou in Mali have brought to light a lithic and ceramic assemblage that dates from before 9400 cal BC. The authors show that this first use of pottery coincides with a warm wet period in the Sahara. As in East Asia, where very early ceramics are also known, the pottery and small bifacial arrowheads were the components of a new subsistence strategy exploiting an ecology associated with abundant wild grasses. In Africa, however, the seeds were probably boiled (then as now) rather than made into bread

Holocene demographic fluctuations, climate and erosion in the Mediterranean: A meta data-analysis

As part of the Changing the Face of the Mediterranean Project, we consider how human pressure and concomitant erosion has affected a range of Mediterranean landscapes between the Neolithic and, in some cases, the post-medieval period. Part of this assessment comprises an investigation of relationships among palaeodemographic data, evidence for vegetation change and some consideration of rapid climate change events. The erosion data include recent or hitherto unpublished work from the authors. Where possible, we consider summed probabilities of 14C dates as well as the first published synthesis of all known optically stimulated luminescence dated sequences. The results suggest that while there were some periods when erosion took place contemporaneously across a number of regions, possibly induced by climate changes, more often than not, we see a complex and heterogeneous interplay of demographic and environmental changes that result in a mixed pattern of erosional activity across the Mediterranean

Les paysages

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Les marais de la basse vallée de la Dives. Contribution interdisciplinaire à l'histoire d'un espace productif et de ses mutations paysagères sur le temps long

International audienc

Phytolith taphonomy in the middle- to late-Holocene fluvial sediments of Ounjougou (Mali, West Africa)

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