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Master Thesis

Potentiel dendrogéomorphologique de deux essences collinéennes de feuillus (Acer opalus, Quercus pubescens) pour l’évaluation de l’emprise spatio-temporelle des chutes de pierres. Le cas de la Croupe du Plantin (Saint-Paul de Varces, massif du Vercors, France)

Abstract : Risk memory at long-term and inventories, especially geomorphologic, have proven to be limited in urbanized areas where the vulnerability associated increases in proportion to urbanization. Rockfall numerical models need to be parametrized and then validated by known events. Tree-ring analyses allow reconstructing past rockfall activity on forested slope at an annual scale. Yet, the reconstruction of rockfall chronologies has been hampered by the paucity of studies that include broadleaved species. This study is going to define the rockfall impacts sensibility of two common and unstudied broadleaved species: Quercus pubescens (Pubescent Oak) and Acer opalus (Italian Maple). The approach is based on the systematic mapping of trees and the counting of visible scars on the stem surface of both species. Data are presented from a site in the Vercors massif (French Alps), where rockfalls are frequently detached from Valanginian limestone marl cliff. A total of 1230 scars were observed on the stem surface of 847 A. opalus and Q. pubescens. Both species present similar spatial distributionof relative rockfall activity with similar downslope decreasing recurrence intervals. By comparing recurrence interval maps obtained from both species and two different tree structures (single trees vs coppice stools) maps based on the Cohen Kappa coefficient and the Mean Absolute Error, this study demonstrate that (i) recurrence intervals vary significantly according to tree species and tree structure; (ii) the recurrence interval observed on Q. pubescens exceeds that of A. opalus of > 20 year in the lower part of the studied plot; and (iii) A. opalus coppice stools do not exhibit a clear spatial pattern. These findings may be explained by the bark thickness and structure of Q. pubescens thougher than A. opalus which constituting a mechanical barrier buffering low energy rockfalls, and avoiding injury to underlying tissues. This master thesis prove the reliability of Q. pubescens and A. opalus for reconstructing rockfall activity and open methodological and practical reflexions on the use of tree-rings and modelling approach for regulatory hazard zoning.
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https://dumas.ccsd.cnrs.fr/dumas-01110605
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Submitted on : Wednesday, January 28, 2015 - 3:15:17 PM
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Adrien Favillier. Potentiel dendrogéomorphologique de deux essences collinéennes de feuillus (Acer opalus, Quercus pubescens) pour l’évaluation de l’emprise spatio-temporelle des chutes de pierres. Le cas de la Croupe du Plantin (Saint-Paul de Varces, massif du Vercors, France). Biodiversité et Ecologie. 2014. ⟨dumas-01110605⟩

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