Abstract
The riparian forests along braided rivers are dynamic, frequently rejuvenated by floods and channel changes, and thus dominated by pioneer to middle stages of succession; they are sites of high biodiversity in some regions. The Lower Eygues River (drainage area 1150 km2 in southeastern France) is such a braided river system with large alluvial forests dominated by Salix alba, Populus alba, and P. nigra. It was identified as a site of ecological interest by the EU under the Natura 2000 program. Such forests elsewhere in Europe have been identified as reference ecosystems. We documented the historical evolution of this alluvial forest from detailed (1:2500 scale) early 19th C parcel maps, early 20th C topographic maps, aerial photography from 1947 to 1996, and field surveys of topography and riparian vegetation in 1997–1998. Our results show that in 1830, the channel was wide, aggraded, and agricultural pressure extended literally to the channel edge. With decline in the rural population and reduced agricultural and grazing pressure in the catchment, erosion rates declined. Reduced sediment supply led to channel narrowing and incision. This channel narrowing, coupled with reduced agricultural pressure along the banks, has allowed riparian forest to colonize former active channel areas, especially within late 19th-century 20th century flood dykes. In recent decades, aggregate mining, and clearing for recreation and agriculture have fragmented the forest. Thus, the alluvial forest of the Lower Eygues is largely an artifact of changing human land-use over the past century, a context that should frame efforts for preservation and restoration.
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Acknowledgements
Data collection and initial analysis for this study was supported by a Fulbright Senior Scholar grant from the Franco-American Commission for Cultural Exchange, and by a contract to support work by the Centre National de la Recherche Scientifique UMR 5600, Lyon from the Syndicat Mixte d’Aménagement Rural de la Drôme and the Syndicats drômois et vauclusiens de l’Eygues. Synthesis and manuscript preparation were supported by a grant under the Alumni Initiatives Award program of Council for International Exchange of Scholars. The staff of the Departmental Archives of the Drôme in Valence was especially helpful in making available departmental records and providing permission to use the cadastral maps. Michelle Bunge, Gretchen Coffman, Margaret Lang, and Steve Railsback helped with the field work. The comments of anonymous reviewers and Associate Editor Tim Kratz substantially improved the paper.
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Kondolf, G.M., Piégay, H. & Landon, N. Changes in the riparian zone of the lower Eygues River, France, since 1830. Landscape Ecol 22, 367–384 (2007). https://doi.org/10.1007/s10980-006-9033-y
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DOI: https://doi.org/10.1007/s10980-006-9033-y