INFLUENCE OF SOME EXTERNAL DEFECTS ON THE RESISTANCE OF TREES TO THE MECHANICAL SIMULATION OF WIND

A simulation of wind action was achieved to test the influence of some external defects on the resistance of standing trees of balsam fir (A bies balsamea (L.) Mill.), yellow birch (Betula alleghaniensis Britton ), and trembling aspen (Populus tremuloides Michx.). The methodology u sed consisted of applying a force on the tree with a winch. Every tree was filmed during winching, and the geometrically corrected images we re used to compute displacement. Balsam fir trees tended to break more than uproot, and,in most cases, breakage occurred at the crack level. Even though maximum turning moment did not differ between control and defective balsam fir trees, a significant difference was found for ma ximum stress, showing a reduction in resistance associated with cracks . No reduction in resistance could be seen for the other species, but trees were relatively young and care should be taken before extending these results to older trees.