Forest carbon accounting methods and the consequences of forest bioenergy for national greenhouse gas emissions inventories

Abstract

While bioenergy plays a key role in strategies for increasing renewable energy deployment, studies assessing greenhouse gas (GHG) emissions from forest bioenergy systems have identified a potential trade-off of the system with forest carbon stocks. Of particular importance to national GHG inventories is how trade-offs between forest carbon stocks and bioenergy production are accounted for within the Agriculture, Forestry and Other Land Use (AFOLU) sector under current and future international climate change mitigation agreements. Through a case study of electricity produced using wood pellets from harvested forest stands in Ontario, Canada, this study assesses the implications of forest carbon accounting approaches on net emissions attributable to pellets produced for domestic use or export. Particular emphasis is placed on the Forest Management Reference Level (FMRL) method, as it will be employed by most Annex I nations in the next Kyoto Protocol Commitment Period. While bioenergy production is found to reduce forest carbon sequestration, under the FMRL approach this trade-off may not be accounted for and thus not incur an accountable AFOLU-related emission, provided that total forest harvest remains at or below that defined under the FMRL baseline. In contrast, accounting for forest carbon trade-offs associated with harvest for bioenergy results in an increase in net GHG emissions (AFOLU and life cycle emissions) lasting 37 or 90 years (if displacing coal or natural gas combined cycle generation, respectively). AFOLU emissions calculated using the Gross-Net approach are dominated by legacy effects of past management and natural disturbance, indicating near-term net forest carbon increase but longer-term reduction in forest carbon stocks. Export of wood pellets to EU markets does not greatly affect the total life cycle GHG emissions of wood pellets. However, pellet exporting countries risk creating a considerable GHG emissions burden, as they are responsible for AFOLU and bioenergy production emissions but do not receive credit for pellets displacing fossil fuel-related GHG emissions. Countries producing bioenergy from forest biomass, whether for domestic use or for export, should carefully consider potential implications of alternate forest carbon accounting methods to ensure that potential bioenergy pathways can contribute to GHG emissions reduction targets.

Net climate impacts of forest biomass production and utilization in managed boreal forests

“…Thus, it is important to consider forest carbon dynamics in climate impacts assessment of bioenergy systems, which has been also argued earlier by McKechnie et al . () and Ter‐Mikaelian et al . ().…”

“…However, the importance of the different timing of carbon emissions from biomass combustion and carbon sequestration in forests and their interactive effects should be considered when planning intensified forest energy biomass production and removal from the mitigation point of view. Trade‐offs between short‐term carbon sequestration benefits and long‐term substitution benefits exist; that is, optimal strategies for forest management and forest biomass utilization affect also the net climate impacts (Sathre et al ., ; McKechnie et al ., ). Using proper management, it is possible either to increase carbon density in forests or to indirectly reduce CO 2 emissions by increasing the use of forest‐based products and energy to substitute fossil‐intensive materials and energy.…”

“…panels, log houses). Thus, the time dependencies of forest carbon uptake and emissions and the residence of carbon in the atmosphere (Ter‐Mikaelian et al ., ; Helin et al ., ; Mitchell et al ., ; McKechnie et al ., ) substantially affect radiative forcing due to the increase/decrease of carbon dioxide in the atmosphere. In the recent assessments, net climate impacts of substitution have been performed using the metric of radiative forcing in case of wood construction (Haus et al ., ) and forest‐based bioenergy (Cherubini et al ., ; Sathre & Gustavsson, , ; Repo et al ., ; Kilpeläinen et al ., ; Kirkinen et al ., ; Holmgren et al ., ).…”

Carbon savings with transatlantic trade in pellets: accounting for market-driven effects

“…Some studies claim that electricity generation from pellets is more carbon intensive than coal (e.g. McKechnie et al 2014, Natural Resources Defense Council 2011, 2014, Walker et al 2010, while other studies claim that forest bioenergy could save 50%-73% of GHG emissions relative to grid electricity (Dwivedi et al 2011(Dwivedi et al , 2014. These assessments were either based on commercially unlikely scenarios involving the use of whole trees for biomass and foregoing high value uses for timber (e.g.…”

“…These assessments were either based on commercially unlikely scenarios involving the use of whole trees for biomass and foregoing high value uses for timber (e.g. Walker et al 2010, McKechnie et al 2014, Natural Resources Defense Council 2011, 2014 or consider only the direct emissions during the production and transportation of pellets assuming no changes in forestlands, harvest rotations, or forest inventories (Damen and Faaij 2006, Magelli et al 2009, Dwivedi et al 2011, 2014, Röder et al 2015.…”