A low-investment technology for the simplified processing of energy wood from coppice forests

A grapple-saw is a low-cost implement, consisting of a hydraulic chainsaw mounted on the frame of a standard log grapple. Grapple-saws are generally installed on forwarders, loaders or modified excavators and are used for crosscutting whole trees or delimbed stems, often as part of a more complex work task such as pre-bunching, loading or stacking. The study analyzed eight different commercial operations where trees were processed with grapple-saws, instead of dedicated cut-tolength processors. All machines in the study were mounted on excavators, but were used under a wide range of stand types and work conditions, although most of the study stands were managed as coppice. Work productivity was determined with time study techniques, which covered the processing of 1800 trees for a total time of 73 h. Productivity ranged between 0.8 and 13 dry t per productive machine hour or between 0.7 and 11 dry t per scheduled machine hour, depending on whether delays (i.e., interruptions of productive work) were excluded or included, respectively. Regression analysis allowed modeling productivity as a function of significant variables, such as tree size, machine type and processing quality. In particular, processing quality was defined as “coarse” when conducted according to lax size and form specifications, or “high-quality” when size and form specifications were strict. The productivity of coarse processing rapidly increased with tree size until the optimum value of 0.3 dry t per tree, and then it slowly declined. The same trend was found for high-quality processing, but in this case optimum tree size was 0.6 dry t per tree. Productivity was higher for landing site work, cold deck operations and coarse processing into tree sections. A dedicated cut-to-length processor is a better choice for matching tight log product specifications, while the grapple-saw is best for handling firewood and chip wood. A grapple-saw is a low-investment piece of equipment for mechanizing small-scale operations, to the benefits of increased productivity, lower processing cost and improved worker safety.