Timber Harvesting and Forest Operations
What this domain tests
Harvest system selection, machine productivity, cost per unit, and the operational and environmental constraints that decide whether a prescription can actually be executed.
Core rules
- Match system to slope, soil, and season. Ground-based skidders and forwarders are generally limited to slopes under about 35 percent and to dry or frozen soils; cable systems reach 35 to 60 percent; helicopters handle steep or sensitive terrain at high cost.
- Production is volume per cycle times cycles per productive hour times utilization. Cost per unit = hourly cost divided by production per scheduled hour. Mixing productive-machine-hours with scheduled hours is the most common arithmetic error.
- Felling can be manual (chainsaw), mechanized (feller-buncher, harvester), or mixed. Delimbing and bucking at the stump versus at the landing change skidding payload and slash distribution.
- Landings, sort yards, and truck access constrain the whole system; undersized landings create bottlenecks that no machine can fix.
- BMPs: avoid wet soils, use designated skid trails, disperse slash off trails, and protect streamside management zones.
Worked example
A grapple skidder averages a 6-minute cycle, so 10 cycles per productive hour, at 3.5 tons per turn: 35 tons per productive hour. At 70 percent utilization that is 24.5 tons per scheduled hour. With a scheduled cost of 120 dollars per hour, skidding costs 120 divided by 24.5 = 4.90 dollars per ton. Using 35 instead of 24.5 would understate cost by 30 percent.
Traps
Quoting production from a different machine or tree size; ignoring utilization; treating forwarders and skidders as interchangeable; assuming a steep slope is fine because the machine can climb it; forgetting that soil moisture can shut a sale down.