Recovery rate of harvest residues for bioenergy in boreal and temperate forests: A review

Harvest residues are an attractive woody biomass feedstock for bioenergy production. A portion of the total harvest residues are generally left in the cutblock due to technical and profitability constraints. A better understanding of the factors influencing the variability of residue operational recovery rate is important to inform accurately policy development on sustainable forest biomass procurement practices. We compiled the results of field trials from boreal and temperate forests to quantify the range of variation of residue recovery rates and to identify the main factors explaining this variability. The average recovery rate was 52.2%, with minimum and maximum values of 4.0 and 89.1%, and a near-normal distribution around the average. The main factor contributing to this variation was country of operations, which encompasses aspects of bioenergy policy and markets, technological learning, and forestry context. A shift in bioenergy policy, a growth in (and a change in access to) bioenergy markets, and upward movements along the technological learning curve could increase residue recovery rates approaching the highest values observed in this study, such as those in Nordic countries (72% residue recovery), or even higher if economic and technological conditions keep improving. However, local stand conditions, especially in North America where natural variability is high among forest stands, may continue to constrain operational recovery of harvest residues. Our results suggest the need for the development of policies that define practices and thresholds based on the ecological suitability of ecosystems, with clear definitions and explicit standards for harvest residue inventory, quantification, and retention. (C) 2014 Her Majesty the Queen in Right of Canada. WIREs Energy and Environment (C) 2014 John Wiley & Sons, Ltd.