Harvest of short rotation woody crops with small to medium size forage harvesters

Abstract. Willow and poplar plantations for short rotation woody crops (SRWC) were originally developed to provide bioenergy and forestry biomass on a large scale. As a consequence, the main harvest technology developed was based on high capacity self-propelled forage harvesters (SPFH) equipped with a special cutter-head. These SPFH are capable of harvesting at an effective rate between 40 and 120 t wet matter (WM)/h with an engine power between 300 and more than 600 kW, and an investment cost between $450,000 and $750,000. The larger SPFH can harvest 15 to 40 ha per day, depending on yield. In reality, SRWC plantations have developed at a relatively small scale in many cases, with average plantation areas of 5 ha in Sweden and typical areas of 3 to 10 ha in England. There is a currently a need and a technology gap for small-to-medium size harvesters, capable of harvesting a wide range of SRWC, especially larger stems (50 to 100 mm diameter), at a rate of about 20 t WM/h which would allow harvesting 3 to 8 ha per day. A small semi-mounted willow harvester (JF192) was operated by a 78 kW tractor and evaluated in a willow plantation. It harvested continuously at an average rate of 15.8 t WM/h, and had effective rates between 8.9 and 11.6 t WM/h when considering time to change hauling tractors and other normal delays (field efficiency from 56 to 73%). It produced filamentous wood chips and could not process adequately stems larger than 50 mm at the point of cut. A medium-size pull-type forage harvester (PTFH), operated in stationary mode with a 94 kW tractor, was fed willow stems up to 98 mm in diameter. It produced sharply cut wood chips, at an average rate of 28 t WM/h with a peak of 38 t WM/h. A novel cutter-head adapted to such a PTFH would be expected to process continuously at least 30 t WM/h with a 150 kW tractor, and have an effective rate of at least 22 t WM/h. Filling such a technology gap would be desirable for future development of SRWC.