Mechanised harvesting of short-rotation coppices

Short-rotation coppice (SRC) is an important source of woody biomass for bioenergy. Despite the research carried out on several aspects of SRC production, many uncertainties create barriers to farmers establishing SRC plantations. One of the key economic sources of uncertainty is harvesting methods and costs; more specifically, the performance of contemporary machine methods is reviewed. We collected data from 25 literature references, describing 166 field trials. Three harvesting systems predominate: 127 used single pass cut-and-chip harvesters, 16 used double pass cut-and-store harvesters, 22 used the cut-and-bale harvester, and one study used a cut-and-billet harvester. Mean effective material capacity (EMC) was 30 Mg fresh weight h-1 (cut-and-chip technique), 19 Mg fresh weight h-1 (cut-and-store technique) and 14 Mg fresh weight h-1 (cut-and-bale technique). However, this comparison does not consider engine power, which varies with harvesting technique; cut-and-chip harvesters are by far the most powerful (>200 kW). When limiting harvesters to a maximum engine power of 200 kW, cut-and-chip harvesters achieved the lowest EMC (5 Mg fresh weight h-1), but they also perform a higher degree of material processing (cutting and chipping) than cut-and-store harvesters (only cutting) or than the cut-and-bale harvester (cutting and baling). The trend in commercial machinery is towards increased engine power for cut-and-chip and cut-and-store harvesters. No trends in EMC were documented for the recently developed cut-and-bale harvesting technique, which is presently produced in one version only. Field stocking (5-157 Mg fresh weight ha-1 in the reviewed studies) has a significant effect on harvester EMC. Lower field stocking can constrain the maximum EMC achieved by the machine given that harvesting speed can only be increased to a point. While the reviewed studies did not contain sufficient harvesting cost data for a thorough analysis, harvesting costs ranged between 6 and 99 € Mg-1 fresh weight.