Abstract
Biomass procured from forests affected by natural disturbances as a bioenergy source is increasingly considered in the context of climate change mitigation. By comparing clearcuts with and without biomass procurement, we aimed to determine the effects of biomass extraction performed alongside lumber harvesting on regeneration density, number of planting microsites, forest renewal costs, and carbon fluxes, in harvested boreal stands affected by spruce budworm. The results showed that biomass procurement increased regeneration density and number of planting microsites. Reduction of downed woody debris due to biomass procurement lowered site preparation costs by 282.07 $CAN·ha−1, equivalent to 14.45 $CAN per oven-dry metric ton (odmt−1) of harvested biomass. Product value from biomass processing had to reach from 13.90 to 76.84 $CAN·odmt−1 to make biomass procurement operations profitable. Since biomass procurement significantly increased stocking and reduced the amount of decaying debris, it also reduced cumulative CO2 emissions relative to scenarios without biomass procurement. However, ensuring forest renewal through site preparation and plantation per se, irrespective of biomass procurement, played a more important role for carbon sequestration and net balance. Integrating biomass harvesting with silviculture could have significant ecological and financial impacts on forest management while supporting mitigation efforts against climate change.
Highlights
Anthropogenic climate change is a growing concern around the world because of its potentially disruptive effects on ecosystems
Since data related to harvested products were not available, the average 212 amount of harvested biomass had to be inferred indirectly. It was calculated by subtracting the average amount of downed woody debris found on cutblocks subjected to biomass procurement from the average amount found on cutblocks without biomass procurement. 216 [APPROXIMATE LOCATION OF FIG. 3] 217 218 Pre-harvest forest cover, regeneration and microsites We estimated pre-harvest forest cover density using governmental forest maps for the study area, and further validated stand density based on the number of stumps
Biomass procurement led to a cost reduction of forest renewal of 14.45 CAD odmt-1 of harvested biomass. Those cost savings were mainly attributable to lower needs of woody debris clearance, scarification and plantation. 426 Site preparation according to biomass volume There was no significant relationship between site preparation costs and the volume of harvested biomass (Fig. 4A)
Summary
Anthropogenic climate change is a growing concern around the world because of its potentially disruptive effects on ecosystems. The Intergovernmental Panel on Climate Change (IPCC) recommended to stabilize atmospheric concentration of CO2 at a maximum of 450 ppm to 2050 (IPCC 2014) To achieve this goal, the IPCC suggests the use of renewable energies as substitutes for fossil energy sources (IPCC 2014; Bacovsky et al 2016). Coniferous stands composed of balsam fir (Abies balsamea (L.) Mill.), white spruce (Picea glauca (Moench) Voss) and black spruce (Picea mariana (Mill.) B.S.P.) are affected by cyclical large-scale spruce budworm (Choristoneura fumiferana (Clemens)) outbreaks, which occur every 30–40 years. This insect causes severe tree defoliation that leads to growth decline and death of the most affected trees (Fig. 1). The time before a bioenergy system using that type of feedstock can reach lower cumulative carbon emissions than an equivalent fossil fuel-based system can be very long, due to the low energy density of wood and the slow decomposition rate of dead trees
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