Mechanical Resistance of Different Tree Species to Rockfall in the French Alps |
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Authors: | Alexia Stokes Franck Salin Adzo Dzifa Kokutse Stéphane Berthier Henri Jeannin Shaun Mochan Luuk Dorren Nomessi Kokutse Murad AbdGhani Thierry Fourcaud |
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Institution: | (1) Laboratoire du Rhéologie du Bois de Bordeaux, Mixed unit: CNRS/INRA/Université Bordeaux I, 69, rte d’Arcachon, 33612 Cestas cedex, France;(2) Forest Research, Northern Research Station, EH25 9SY Midlothian, Scotland;(3) Cemagref Grenoble, 2 rue de la Papeterie, B.P. 76, 38402 St. Martin d’Hères cedex, France;(4) AMAP, CIRAD, TA40/PS2, Boulevard de la Lironde, 34398 Montpellier Cedex 5, France |
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Abstract: | In order to determine the mechanical resistance of several forest tree species to rockfall, an inventory of the type of damage
sustained in an active rockfall corridor was carried out in the French Alps. The diameter, spatial position and type of damage
incurred were measured in 423 trees. Only 5% of trees had sustained damage above a height of 1.3 m and in damaged trees, 66%
of broken or uprooted trees were conifers. Larger trees were more likely to be wounded or dead than smaller trees, although
the size of the wounds was relatively smaller in larger trees. The species with the least proportion of damage through stem
breakage, uprooting or wounding was European beech (Fagus sylvatica L.). Winching tests were carried out on two conifer species, Norway spruce (Picea abies L.) and Silver fir (Abies alba Mill.), as well as European beech, in order to verify the hypothesis that beech was highly resistant to rockfall and that
conifers were more susceptible to uprooting or stem breakage. Nineteen trees were winched downhill and the force necessary
to cause failure was measured. The energy (E
fail) required to break or uproot a tree was then calculated. Most Silver fir trees failed in the stem and Norway spruce usually
failed through uprooting. European beech was either uprooted or broke in the stem and was twice as resistant to failure as
Silver fir, and three times more resistant than Norway spruce. E
fail was strongly related to stem diameter in European beech only, and was significantly higher in this species compared to Norway
spruce. Results suggest that European beech would be a better species to plant with regards to protection against rockfall.
Nevertheless, all types of different abiotic stresses on any particular alpine site should be considered by the forest manager,
as planting only broadleaf species may compromise the protecting capacity of the forest e.g. in the case of snow avalanches. |
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Keywords: | protection forest tree stability root anchorage uprooting stem breakage scar formation |
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