Analyses of a single-machine system for harvesting pulpwood and/or energy-wood in early thinnings

Abstract

Harwarder systems used in roundwood harvesting can be useful at sites where there are low volumes per hectare to be removed or a small total removal volume and where frequent or long-distance machine relocations are required. As well as being suitable for conventional roundwood harvesting, a multi-purpose forest machine can have its configuration changed, so that it can function as a harvester, forwarder, or harwarder, and thus can be considered viable for use in young stands when harvesting pulpwood or energy-wood or combining assortments. Accordingly, in this study we compare the time consumption and productivity of a Ponsse Dual machine system with two harvesting heads and one loading grapple (three machine configurations) when harvesting and forwarding pulpwood and/or energy-wood during early thinning at sites in northern Sweden. Our aim is to analyze costs and profitability under a range of site conditions. Working as a harvester, the machine reached the same level of productivity (trees per hour) whether it was operating with an accumulating felling head or a harvester head able to accumulate some trees; productivity was also independent of work method. The forwarding efficiency was highly correlated with biomass concentration and forwarding distance; whole-tree (tree section) removal over short forwarding distances resulted in the highest productivity. The system achieved the greatest cost-effectiveness when only energy-wood was removed. At current market prices, pulpwood extraction produced the highest net income per hectare, but even this was economically unprofitable. The Ponsse Dual achieves similar productivities to specialized harvesters and forwarders during thinning operations, but at a much higher cost per operating hour. Thus, a single-machine system would need to have ca. 20–30% lower operational costs than the Ponsse Dual to be an economically viable option for early thinning.