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Response of Coniferous Trees to Wind Loading

Response of Coniferous Trees to Wind Loading. John Moore. Introduction. Effects of wind on trees and stands seed and pollen dispersal influence on mass exchange (i.e., CO 2 and water vapor) stem form and growth patterns damaging effects uprooting, stem breakage loss of foliage.

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Response of Coniferous Trees to Wind Loading

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  1. Response of Coniferous Trees to Wind Loading John Moore

  2. Introduction • Effects of wind on trees and stands • seed and pollen dispersal • influence on mass exchange (i.e., CO2 and water vapor) • stem form and growth patterns • damaging effects • uprooting, stem breakage • loss of foliage

  3. Damaging Effects of Wind • Uprooting and breakage of trees are important stand replacing disturbances. • In managed forests they are generally viewed in a negative light. • In many areas of the world, wind is a major constraint on forestry

  4. Modeling Wind Damage • Empirical approaches • analysis of sample plot data • retrospective studies • Mechanistic approaches • static • dynamic

  5. Dynamic Response • Trees are dynamic structures which respond to the fluctuating wind forces acting on them • Two approaches to modeling dynamic response of trees to wind: • mechanical transfer function • dynamic structural model of tree

  6. Wind speed Tree movement y(t) u(t) Transfer function 1. Mechanical Transfer Function Measure both wind speed and tree response

  7. Example in Douglas-fir

  8. 2. Dynamic Structural Model • Predict response of trees to an applied wind force • Dynamic motion of tree described by the following equation:

  9. Model Requirements • Need information on the following: • Natural frequency of tree • Damping ratio • Applied bending moment • These can be predicted from a knowledge of the within-stand wind speed profile and tree size

  10. Natural Frequency & Damping

  11. Relationship to Tree Size

  12. Applied Bending Moment Wind h Center of mass d

  13. Factors Affecting Applied Bending Moment • Within-stand wind speed • Crown size and shape • Foliage drag coefficient • Stem stiffness • Height to center of mass • Presence of snow or ice

  14. Crown Size and Shape • Drag force acting on crown is a function of crown frontal area • Damping is also a function of crown mass and its distribution

  15. Crown Shape Models • Engineering theory in mechanistic models is quite advanced • Mensurational information is quite primitive!

  16. Crown Shape Assumptions GCL CW

  17. Conclusions • Mechanistic models can provide useful information on the risk of wind damage • Present models may suffer because the mensurational information they use does not match their level of engineering sophistication

  18. Acknowledgements Starker Forests Mark Gourley OSU Dr Doug Maguire Tim Vredenburg Andrew Brickman Milo Clauson

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