Fourteen yarding settings on eight different sites on the Queen Charlotte Islands were monitored to measure productivity and evaluate logging system effectiveness, to document yarding disturbance, and to determine how disturbance may contribute to landslide initiation. Twenty-three landslides occurred on or near the study areas, of which three occurred in adjacent control areas of no logging, and four occurred prior to yarding and were probably associated with discharge of road drainage. Of the sixteen failures that occurred within the yarded areas, fourteen had direct evidence of yarding disturbance in their initiation zones.
Nine of the failures (four road associated, three non-logging associated, and two yarding associated were over 200 m2 in area). For the area of the study (1.065 km2), and the time period (4 years since falling and 3.6 years since yarding), the frequency for logging failures (road and yarding) was 1.4 failures per km2 per year, and for yarding failures was 0.5 failures per km2.
The report describes various logging terms, yarding systems, and yarding disturbance forms. Production and yarding costs for highlead, mobile yarding crane (grapple and dropline carriage), and skyline yarding are presented. Operational factors that limit or promote particular system use on steep difficult terrain are documented.
The amount and causes of yarding disturbance are documented and related to the terrain yarding system requirements, yarding techniques, and operation. The importance of other factors (including falling of timber and vegetation removal) are also noted. The number, apparent causes, size, and time period of mass-wasting events are documented and setting.
The characteristics of sensitive sites on the areas studied are noted.
Recommendations are made that can assist logging engineers and loggers in reducing yarding disturbance, increasing productivity, and reducing the potential for yarding-induced mass wasting.
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Updated December 03, 2008