Wind profiles and mechanical resistance of uprooted trees in a Japanese cypress (Chamaecyparis obtusa) plantation slightly damaged by Typhoon Melor 0918 at Kamiatago Experimental Forest, Tenryu, Japan : Validity of mechanistic models for wind damage risks

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  • 台風0918号により天竜・上阿多古演習林ヒノキ林で発生した風害被害木近傍の風速垂直プロファイルと力学耐性 : 風害リスク評価力学モデルの妥当性
  • Wind profiles and mechanical resistance of uprooted trees in a Japanese cypress (Chamaecyparis obtusa) plantation slightly damaged by Typhoon Melor 0918 at Kamiatago experimental forests, Tenryu, Japan: validity of mechanistic models for wind damage risks

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In 2009, Typhoon Melor (0918) uprooted trees in a 67-year-old Japanese cypress plantation in the Kamiatago Experimental Forest of Shizuoka University, Tenryu, Japan. Before the typhoon, we had installed anemometers in the forest and conducted tree-pulling trials to construct a model to evaluate the wind damage risk. The unpredictable disturbance event of Typhoon Melor enabled to us to 1) clarify the attributes of trees that show high wind damage risk from both observational and mechanistic aspects, 2) document wind profiles under strong winds that cause uprooting, and 3) discuss the validity of previous models for wind damage risk by comparing them to events that occurred during the typhoon. The proportion of crown size to diameter at breast height was a significant factor for predicting tree damage, but stem taper and tree size were not significant factors. When the wind velocity at 30m height exceeded approx. 7ms^<-1>, there were drastic changes in the vertical wind profile, including an increase in the gradient of wind velocity just above the canopy. For damaged trees, the critical wind speeds calculated using the GALES models were almost three times the maximum mean wind speed observed during the disaster term. The most significant problem in using the models lay in the large discrepancy between the model and actual observations with respect to the pattern of vertical wind profiles in strong wind conditions. These results suggest that it is not valid to use aerodynamic parameters of classical logarithm law in wind damage risk models. However, in terms of tree attributes, the vulnerability of trees predicted by the model was consistent with the observed vulnerability. These results show that the model has some validity in evaluating damage risk based on tree attributes.

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