Modelling Harvester-Forwarder System Performance in a Selection Harvest

A harvester – forwarder system was studied in a selection harvest operation conducted in an interior forest stand composed of Douglas fir (Pseudotsuga menziesii), Ponderosa pine (Pinus ponderosa), and Grand fir (Abies grandis). A time-study analysis was used to develop models for predicting individual machine productivity over time for both the harvester and forwarder involved in the study. Analysis indicates that harvester productivity (13.85 m3 per SMH) closely matched forwarder production (14.10 m3 per SMH) during the study. Further analysis yielded models that can be used to predict system productivity across the range of stand values observed during the study. The results suggest that system productivity is balanced when operating in stands averaging 15 to 25 cm DBH. In stands of larger or smaller average diameter, productivity for the system becomes unbalanced and affects machine operation, particularly the forwarder. Further research is suggested to improve the developed predictor models and allow for prediction of system performance over a broad range of stand and site conditions.