Partial Retention and Helicopter Turn Volume‪.‬

Abstract Helicopter logging may be used to harvest partial retention silviculture systems. The high cost of operating helicopters drives the need to maximize turn volumes; however, previous researchers have noted that turn size may decrease at higher retention levels. This study examined three units of a helicopter logging operation that had different levels or patterns of partial retention. As is common in case studies in forest operations, there were numerous confounding effects between the units. The confounding effects were efficiently dealt with by employing regression analysis and indicator variables, where the indicator variables carry the variation attributed to the different units. After taking into account the explanatory variables logDEN and logLV, the indicator variable for the unit with 40 percent dispersed retention was significantly different from the indicator variables for the unit with 40 percent aggregate retention and the unit with 15 percent dispersed retention; however, the indicator variable for the unit with 40 percent aggregate retention was not significantly different from the indicator variable for the unit with 15 percent dispersed retention. Therefore, given the difficulties the hooktenders had in building turns in the unit with 40 percent dispersed retention, it is likely the high level of dispersed retention in this unit affected the turn volume, while the patterns or levels of retention in the other units did not.