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Three-dimensional modelling of slope stability in heterogeneousmontane forest ecosystems

Mao Z., Bourrier F., Stokes A., Fourcaud T.. 2014. Ecological Modelling, 273 : p. 11-22.

DOI: 10.1016/j.ecolmodel.2013.10.017

Vegetation can play an important role in stabilizing soil against shallow landslides. Using a three-dimensional (3D) finite element method, we developed a model to study the impact of differentmanagement scenarios on slope stability in mountain forests. Ground truth data were obtained froma mixed forest ecosystem situated at an altitude of 1400 m a.s.l. in the French Alps. Five scenarios rep-resenting the forest at different spatial and temporal stages of management were selected: [A] bare soil,[B] tree island (i.e. tree groups growing in clusters) on bare soil, [C] new gap (i.e. canopy free zones withlittle understorey) in homogeneous forest, [D] old gap (i.e. canopy free zones with abundant understorey)in homogeneous forest and [E] homogeneous forest. For scenarios [B], [C] and [D], the locations of thevegetated patch along the slope (top, centre and toe) were also tested, to determine if vegetation patternsinfluenced slope stability. As plant roots play a crucial role in reinforcing soil, we altered the 3D spatialdistribution of root density in the model using real data. By calculating the factor of safety (FoS), i.e. ameasure of the likelihood that the slope will fail, we show that slope morphology, including angle andsoil depth, play an essential role in slope stability. Vegetation also exhibited a positive effect on slopestability, but the efficiency of this effect was significantly influenced by slope morphology and root distri-bution with regard to soil depth. In particular, if a layer of soil beneath the most superficial rooting zonecontained few roots, slope integrity was compromised. Compared to bare soil, the FoS increase due tovegetation was only ?0.2 (i.e. ?15%), when deeper soil layers contained few or no roots. However, if thesoil profile contained roots throughout, the FoS increase was >25% higher. We highlight the importanceof taking into account spatial complexity and refining the output, i.e. FoS, during the modelling of slopestability, which can only be achieved through the use of 3D models. (Résumé d'auteur)

Mots-clés : forêt; stabilisation du sol; région d'altitude; terre en pente; modèle mathématique; aménagement forestier; enracinement; système racinaire; profondeur; france; densité de plantation

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