The loading of second-growth Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco): to simulate the forces acting on an intermediate support tree

The comercial thinning of second-growth stands in the Pacific\ud Northwest is becoming increasingly important for satisfying the demand\ud for timber. Cable logging will require the rigging of smaller intermediate\ud support trees rather than those utilized on old-growth timber sales.\ud This paper reports on the results of a study designed to evaluate the\ud ability of second-growth trees to sustain the compressive forces similar\ud to those generated by a cable logging system.\ud The movements of nine trees subjected to increasing amounts of force\ud were measured with two theodolites. The conditions of loading were\ud similar to those imposed on intermediate support trees.\ud The study demonstrates that a tree will continue to move in the\ud direction of its initial lateral movement. Once a tree is bent, the\ud downward compressive force governs the movement of the tree.\ud The results from the study are compared to Euler's design formula.\ud It is suggested that a factor of safety be applied when designing an\ud intermediate support. Additional research is proposed by the author\ud to determine the forces acting on support trees during the actual\ud yarding cycle