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