Harvesting Short-Rotation Poplar Plantations for Biomass Production

In Italy, short rotation forest has become very popular in recent years, with over 4,000 hectares already planted - almost exclusively with clone poplar. The study models the performance of modified forage harvesters on a range of short-rotation poplar plantations, identifies technical obstacles to the deployment of these machines and suggests solutions that may expand the capability of modified forage harvesters when treating short-rotation poplar. Data were collected from 16 operations, covering a total of 50 hectares and producing over 1000 green tonnes of wood chips. The average yield of the fields harvested during the trials was about 20 green tonnes/ha year, equivalent to 8 oven-dry tonnes/ha for a 60% average moisture content, measured in the laboratory. Gross machine productivity ranged from 9 to 44 green tonnes/scheduled machine hour (gt/SMH), with an average value of 25 gt/SMH. Of course, this result is affected by other factors than just forager performance, which is potentially much higher. A model was developed to predict harvesting performance and cost, showing that harvesting cost can be maintained below the 15 Euro/green tonne (2 Euro/GJ) ceiling only if field stocking exceeds 40 or 50 gt/ha when rows are long 300 and 100 m, respectively. The study also shows the need to optimize operations. Over a quarter of the total worksite time is occupied by unproductive delays, which may be reduced with improved planning and maintenance.