A-horizon dynamics in a historical hedged landscape

In hedged landscapes, the hedge structure induces a modification of soil organization at the landscape scale and another modification of soil geometry and properties at the slope scale. In these environments, the effects of landscape structures on soil pedogenesis and properties are identified, yet the time scale on which the target processes are occurring remains unknown. The aim of this paper is to constrain the space and time changes in hedge structure, within a historical hedged landscape, in order to better quantify the dynamics of A-horizons geometry. To achieve this goal, we implemented various relative methods (soil geometry analysis, historical document analysis) and absolute methods (14C, 137Cs). Results highlight the complexity of soil spatial organization within the landscape: A-horizon geometry is clearly influenced by landscape structures, whereas deeper horizons appear not to be influenced by these structures. The explanatory factors of this current organization are not only the present topography and hedgerow network pattern, but also the position of former hedgerows. Organo-mineral horizon changes clearly post-date the establishment of the hedgerow network landscape, which has controlled topsoil horizon geometry. Since 1833, the decrease in hedgerow network density has changed the spatial distribution of soil redistributions through diffusive transport (including tillage translocation) and water erosion processes; locally, it has increased soil erosion processes with respect to the increase in uphill drainage surface areas without changing general soil organization at the landscape scale acquired over the longer term.