Abstract
Mountainous hardwood mixed stands offer challenges to timber harvesting operations in practice, including a harsh climate, variable topography, steep terrain, and large-sized timbers. This paper aims to develop productivity and cost models for a mountain-ground-based harvesting operation across the terrain (e.g., slope conditions), stand (e.g., tree volume) environmental (e.g., weather), and yard (e.g., winching distance) variables and to assess GHG emissions related to the equipment in use. This development was implemented in a timber harvesting practice under single-tree selection in mountainous forests of Iran where a motor-manual chainsaw is used for felling and a rubber-tired cable skidder is used for log extraction. The average delay-free productivity was 4.55 m3 for felling and 14.73 m3 h−1 for skidding. Lower production costs and higher productivity rates were observed over the gentle slopes and in sunny conditions. The average production costs ranged between USD 4.27 m−3 for felling and USD 5.35 m−3 for skidding. The average emissions ranged between 0.96 kg m−3 for felling and 7.06 kg m−3 for skidding in snowy conditions over steep slopes. The study’s results confirm avoiding harvesting operations on steep slopes (greater than 35%) and in extreme weather conditions to obtain higher work efficiency and to minimize adverse effects of machinery on forest ecosystems. The results should be of use to harvest managers and forest planners considering the application of ground-based harvesting operations using a semi-mechanized system on a range of operating conditions in mountain hardwood stands.
Highlights
This study provided detailed information about the time elements, productivity, cost, and greenhouse gas (GHG) emissions associated with upstream activities of forest operations on steep slopes under a ground-based harvesting operation
The results demonstrate that the effects of slope gradients and weather conditions may create challenging conditions for mountain harvesting operations
We recommended that harvesting operations be scheduled to occur during sunny weather and that skidding operations on steep slopes be avoided in order to obtain higher safety and work efficiency and to minimize the adverse effects of machinery on forest ecosystems
Summary
Various factors and constraints contribute towards a successful harvest operation These constraints often discourage deployment of the fully mechanized system (e.g., a combination of harvesters and forwarders), and harvesting contractors are forced to use the purpose-built steep terrain equipment to improve the productivity and reduce the harvesting costs [1] while minimizing the adverse environmental impact. Mechanization of forest operations in these regions often encourages the use of semi-mechanized equipment such as a combination of motor-manual felling and ground-based skidding vehicles including crawler skidders or rubber-tired cable skidders [2]. This is mainly due to the advantages of the productivity, low purchase cost, ease of service, and moderate skill requirements [3]. Different harvesting methods can be applied depending on a number of factors
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