Four landing biomass recovery case studies in New Zealand clear-cut pine plantations

Abstract

New Zealand forest operations are primarily based on large scale pine plantation clear-cuts. Previous studies have shown that relatively large volumes of woody biomass residues accumulate at the landings. This includes not only the branches and tops, but a very aggressive value recovery program focusing on quality results in a large volume of relatively short large diameter off-cuts. Through a program supported by the NZ Energy Efficiency and Conservation Authority (EECA), four field studies were carried out to assess productivity characteristics and logistical options to optimise the recovery of landing biomass. The first field trial looked at using a tub grinder to comminute very large, but contaminated volumes of biomass from a superskid, whereby a comparison was made between fresh and old residues. The second looked at recovering short logs from the biomass piles and loaded directly by excavator into a bin truck, or stacked for a self-loading truck. The third focussed on longer logs trucked to a centralised landing area: the resulting stack covered for drying and subsequently chipped. For the latter study, an additional trial was set up to assess moisture content change over time of timber stacked, with treatments of covered and larger logs split. At time of writing the fourth trial had yet to commence. The results to date indicate that the difficulty of recovering the biomass from the landings significantly impact the ability to comminute cost-effectively. Sieving tests of the comminuted biomass indicated high levels of contamination, with large percentages of fines. While system costs were comparably moderate, production levels were low given the size and potential of the equipment used.