Efficiency of Topping Trees in Cable Yarding Operations

The extraction of biomass and nutrients out of the forest is implicit to every harvest operation. In cable yarding, whole-tree harvesting (WTH) has become more prevalent in the last few decades and processing takes place at the roadside. There is a concern that WTH impairs site productivity due to nutrient removal. One option to increase the amount of biomass remaining in the stand is to top the trees before extraction. In order to estimate the influence of topping on system productivity, time studies on a medium-sized tower yarder were carried out in three spruce dominated stands. Heart rate monitoring of the chainsaw operator was performed to examine the physiological workload. The analysis showed that topping only impacts system productivity if it takes place during the inhaul of the load as it leads to interruptions of the extraction progress. These interruptions took on average 13 seconds per turn. In addition, if topping was performed on already lifted trees, a reduction of line-speed during the lateral yarding of the loads was observed. This led to a reduction in productivity between 5 and 11%, assuming that all trees would have been topped during the lateral yarding process. Analyses of the physical workload of the chainsaw operator showed that the workload of topping trees is significantly lower than that of the felling process. Relative heart rate of the subject was lower at the cable corridors where topping was ordered. This confounding result may be a consequence of many additional factors like slope gradient or cycle time. Under both scenarios, the worker never surpassed the limit of a sustainable cardio-vascular workload for an 8 hour working day. Hence, recovery time for the chainsaw operator can be considered as adequate when topping is performed in a three-man crew.