Question 1 of 8: Harvest Systems — Definition, Types and Equipment

Question 1: Harvest Systems — Definition, Types and Equipment (20 marks)

Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.

A harvest system is the organized combination of machines, methods and sequenced work tasks used to convert standing timber into merchantable products delivered to roadside or to a mill, spanning felling, primary transport (extraction), in-woods processing (delimbing, bucking, sorting) and secondary transport (hauling). A system is defined less by any single machine than by where and how the stem is broken down — at the stump, at roadside, or not at all until the mill — because that choice fixes which machines are needed, how they interact, and the productivity, cost and environmental footprint of the whole operation. Three harvest systems dominate the Canadian forest industry, distinguished by the state in which the stem leaves the stump.

Full-tree system. The entire tree, with limbs and top still attached, is felled and bunched at the stump, then extracted whole to a roadside landing where it is delimbed, topped and bucked into merchantable lengths before being loaded onto trucks. This is the traditional system on much of BC's Interior dry-belt terrain and remains common where landing space, terrain and stand characteristics favour centralizing processing at roadside. A mechanical feller-buncher (a swing-boom or drive-to-tree machine with a shear or hot-saw felling head) fells and accumulates several stems into a bunch; a grapple skidder then grapples a bunch and drags it, whole tree, to the landing over the ground (or a cable/high-lead yarder does the equivalent on steep coastal terrain, where a mainline and carriage haul turns of trees uphill or downhill to a landing that machines cannot safely reach). At the landing, a delimber/processor (or a static delimbing gate plus a stroke or slasher unit) strips limbs and tops and bucks the stem to length, and a log loader sorts and loads the resulting logs onto highway trucks.

Tree-length system. The tree is felled and delimbed (and sometimes topped) at or near the stump, so what travels to the landing is a long, limb-free stem rather than a whole tree; final bucking into merchantable log lengths happens at the landing. A hand faller with a chainsaw, or a felling head that both shears and strips limbs, does the stump-side work; a grapple skidder or forwarder then extracts the delimbed stems to roadside, where a mobile or stationary slasher (multi-saw bucking unit) cuts them to length before loading. Tree-length sits between full-tree and cut-to-length: it removes the bulky, low-value slash from the extraction load (lighter skidder payload of merchantable wood, less landing debris than full-tree) while still centralizing the length-optimization decision at roadside rather than in the stand.

Cut-to-length (CTL, shortwood) system. A single machine, the harvester (an excavator-base carrier with a processing head that fells, delimbs, measures and bucks in one continuous pass), converts the standing tree directly into merchantable-length logs at the stump, guided by an onboard computer that optimizes bucking against current market log specifications. A forwarder (a self-loading, load-carrying machine, not a drag-type skidder) then picks the sorted logs off the ground with its own grapple/crane and carries them, fully supported off the ground, to roadside for direct truck loading. CTL is now the dominant system across most of eastern and boreal Canada and is increasingly used in BC on gentler terrain, because it leaves limbs and tops (and the nutrients they hold) scattered through the stand, minimizes soil disturbance (the forwarder rides on its own brush mat of slash), and lets the harvester's computer control value recovery stem by stem.

The three systems therefore differ along one continuous axis — how much stem-breakdown work is done in the stand versus at the landing — and that single difference cascades into every other distinction between them: extraction-load composition (whole tree vs. delimbed stem vs. finished log), number and specialization of machines, landing space and slash-handling requirements, soil-disturbance and nutrient-retention outcomes, and where in the chain value-recovery/bucking decisions are made. Coastal steep-slope terrain, where ground-based machines cannot operate, typically forces a fourth transport mode — cable yarding — onto whichever felling/processing combination is used, but the felling-processing classification above still governs how the turn is broken down once it reaches the landing.