Fully mechanized harvesting systems are the most productive and common harvesting systems in the United States.
Stem size, stand density, species composition, silvicultural prescriptions, slope/terrain, and operator skill affect the productivity and cost of a harvesting system. Timber harvest expectations of foresters, landowners, and loggers are dependent on these factors. A new article describes the factors affecting the productivity of specific harvesting machines used in whole-tree harvesting and its impact on harvesting cost. The article summarises the main factors which affect system productivity.
- Stem Size: Stem size is a significant factor that affects the productivity of the feller-buncher. Relatively large trees allow the machine to cut greater volumes of wood per machine hour.
- Skidding Distance: The efficiency of a skidder is greatly affected by skidding distance because it strongly affects the skidding time.
- Stand Density: The lower the stand density, the larger the distance between harvested trees. The time spent on driving to every single tree that is being harvested increases when tree spacing is increased. However, the larger volume of trees typically associated with a low stand density can compensate for this decrease in production and result in greater net productivity.
- Species Composition: Pull-through delimber productivity depends on the characteristics of tree species and varies mostly with the hardwood content of a stand and the thickness of branches. The productivity of the pull-through delimber is lower in hardwood stands than in softwood stands.
- Silvicultural prescription: Silvicultural prescription determines the type, quality, and quantity of wood to be harvested and significantly affects the productivity of harvesting operations. Generally, harvesting productivity increases with higher removal intensity.
- Slope: Steep slopes and uneven terrain negatively impact harvesting productivity. Slope is an important determinant of machine stability, impacting travel speed, and duration of the work. Steep slopes also pose considerable safety concerns for equipment operators. As slope increases, the productivity of harvesting equipment decreases.
- Operator: The skill of the operator plays an important role in determining the productivity of the harvesting equipment. The difference in productivity is due to different cutting techniques, work experiences, work planning, felling order, and operators’ dexterity. The operator has some control over the average skid distance and the size of payload per cycle which can impact the productivity of the skidder. Operator skill in combination with the machine and site condition affects the efficiency of the grapple skidder and feller-buncher by up to thirty percent. An operator also plays a vital role in controlling stand damage caused by harvesting equipment.
The authors were Parajuli, Manisha; Hiesl, Patrick; Smidt, Mathew; Mitchell, Dana. The article was produced in 2020 and is titled “Factors influencing productivity and cost in the whole-tree harvesting system”.