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Windthrow Mechanics

Applied forces. Show Larger Image

What do you already know about how wind interacts with trees?

Applied Forces
  • Trees are like big levers. They are attached at the bottom and free swaying at the top.
  • The crown of the tree is like a sail. Wind acting on the crown creates a 'drag force.' This drag force is multiplied by the lever arm to produce a turning moment around the point of attachment.
  • Because trees are flexible, the crown is displaced. The mass of the crown is multiplied by the length of displacement to produce an additional turning moment.
  • As trees grow taller, the length of the lever arm increases. This means that the turning moment will increase even if the crown stays the same size.

Forest Service BC
 
Forest Renewal BC