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The root-soil system of Norway spruce subjected to turning moment: resistance as a function of rotation

  • Lundström, Tor WSL, Swiss Federal Institute for Snow and Avalanche Research SLF, Davos Dorf, Switzerland - Laboratory of Dendrogeomorphology, University of Fribourg, Switzerland
  • Jonsson, Martin J. WSL, Swiss Federal Institute for Snow and Avalanche Research SLF, Davos Dorf, Switzerland
  • Kalberer, M. WSL, Swiss Federal Institute for Snow and Avalanche Research SLF, Davos Dorf, Switzerland
    20.09.2007
Published in:
  • Plant and Soil. - 2007, vol. 300, no. 1-2, p. 35-49
allometry
energy absorption capacity
protective forest
mechanical modeling
tree structure
uprooting process
English The reactions of trees to wind, rockfall, and snow and debris flow depend largely on how strong and deformable their anchorage in the soil is. Here, the resistive turning moment M of the root–soil system as a function of the rotation ϕ at the stem base plays the major role. M(ϕ) describes the behavior of the root– soil system when subject to rotational moment, with the maximum M(ϕ) indicating the anchorage strength M a of the tree. We assessed M(ϕ) of 66 Norway spruce (Picea abies L. Karst) by pulling them over with a winch. These 45- to 170-year-old trees grew at sites of low and high elevation, with a diameter at breast height DBH = 14–69 cm and a height H =  9–42 m. M(ϕ) displayed a strong nonlinear behavior. M a was reached at a lower ϕ for large trees than for small trees. Thus overhanging tree weight contributed less to M a for the large trees. Overturning also occurred at a lower ϕ for the large trees. These observations show that the rotational ductility of the root–soil system is higher for small trees. M a could be described by four monovariate linear regression equations of tree weight, stem weight, stem volume and DBH ² ·H (0.80 < R ² < 0.95), and ϕ at M a, ϕ a, by a power law of DBH²·H (R ² = 0.85). We found significantly higher M a for the low-elevation spruces than for the high-elevation spruces, which were more shallowly anchored, but no significant difference in ϕ a. The 66 curves of M(ϕ), normalized (n) by M a in M-direction and by ϕ a in ϕ-direction, yielded one characteristic average curve: Mn (ϕn) M¯nϕn . Using this average curve and the predictions of M a and ϕ a, it is shown that M(ϕ) and the curves associated with M(ϕ) can be predicted with a relative standard error ≤25%. The parameterization of M(ϕ) by tree size and weight is novel and provides useful information for predicting with finite-element computer models how trees will react to natural hazards.
Faculty
Faculté des sciences et de médecine
Department
Département de Géosciences
Language
  • English
Classification
Biological sciences
License
License undefined
Identifiers
Persistent URL
https://folia.unifr.ch/unifr/documents/300523
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