Economics of forest biomass for bioenergy: potential site preparation savings from coarse woody harvesting residue removal in a short-rotation Eucalyptus globulus (Labill.) plantation
The study used time studies and cost analysis to assess potential economic benefits from site preparation cost reductions resulting from producing coarse woody harvesting residue (CWHR) for bioenergy. In contrast, previous studies have predominantly used anecdotal estimates of site preparation costs.The study was performed in a recently clearfelled 15-year-old plantation of Eucalyptus globulus (Labill) in Tasmania, Australia. The study area consisted of the control area (0.51 ha), containing ~35 m3 ha-1 of CWHR and the CWHR harvest area (2.47 ha), containing ≤12 m3 ha-1 of CWHR. The control area had been harvested with a harvester – forwarder system, which left all harvesting residue (HR) onsite, where-as the CWHR harvest area had been harvested with a feller-buncher – skidder – processor system which removed most of the HR. The latter site was used to simulate an area where CWHR had been harvested. The study examined productivities and costs of machines performing site preparation in each area. The preparation of the control area site was performed with an excavator that windrowed CWHR, fol-lowed by a skidder-mounted plough constructing planting furrows. Residual CWHR post-windrowing was <1 m3 ha-1. Productivities and costs were 0.53 ha PMH0-1 and AUD$319 ha-1 for the excavator and 1.1 ha PMH0-1 and AUD$139 PMH0-1 for the skidder-mounted plough. The excavator was not required in the CWHR harvest area. In this area, skidder-mounted plough productivity and cost were 1.16 ha PMH0-1 and AUD$109 ha-1 suggesting CWHR reduction to ≤12 m3 ha-1 could reduce site preparation costs by AUD$319 ha-1. Further studies on costs and revenues associated with CWHR removal and sale are required to determine net economic benefits and determine excavator cost and productivity for a range of CWHR quantities.
