No abstract

The forest sector can help reduce atmospheric CO2 through carbon (C) sequestration and storage and wood substitution of more polluting materials. However, climate change can have an impact on the C fluxes we are trying to leverage through forestry. We calculated the difference in CO2 eq. fluxes between ecosystem-based forest management and total forest conservation in the context of the temperate-boreal forest ecotone of Quebec (Canada), taking into account fluxes from forest ecosystems, wood product life cycle, and the substitution effect of wood products on markets. Over the 2020–2120 period, in the absence of climate change, ecosystem-based forest management and wood production caused average net annual emissions of 66.9 kilotonnes (kt) of CO2 eq. year−1 (relative to forest conservation), and 15.4 kt of CO2 eq. year−1 when assuming a 100% substitution effect of wood products. While management increased the ecosystem C sink, emissions from degradation of largely short-lived wood products caused the system to be a net source. Moreover, climate warming would decrease the capacity of ecosystems to sequester C and cause a shift towards more hardwood species. Our study highlights the need to adapt the industrial network towards an increased capacity of processing hardwoods into long-lived products and/or products with high substitution potential.

The contribution of the forest sector to climate change mitigation needs to rely on optimal strategies that include forest management, wood supply, wood product disposal, and replacement of GHG-intensive materials and energy sources. Our study aimed to assess the impact of alternative forest management practices applied at the stand scale on the capacity of the forest sector to reduce its radiative forcing, using the boreal forests of eastern Canada as a case study. We simulated management of a balsam fir–white birch stand over a sixty-year period and determined the sectorial carbon and radiative forcing budget for a reference scenario (no harvest) and for nineteen clearcut and partial cut alternatives. The results suggest that logging may not significantly reduce carbon emissions compared to a preservation practice and does not yield any climate benefits in terms of radiative forcing. In a context for which the substitution effect of wood products on markets is expected to be limited, the mitigation potential of a scenario is mostly driven by the capacity of the forest ecosystem carbon sink to compensate for the substantial CO2 and CH4 emissions from wood product decay in landfills. The improved assessment of carbon emission temporality, incorporation of ecosystem carbon dynamics, and improved consideration of substitution and the decay of wood products are essential in the development of any forest management strategy. Neglecting these elements can lead to misconceptions and prevent informed mitigation decisions.

Global pathways limiting warming to 2 °C or below require deep carbon dioxide removal through a large-scale transformation of the land surface, an increase in forest cover, and the deployment of negative emission technologies (NETs). Government initiatives endorse bioenergy as an alternative, carbon-neutral energy source for fossil fuels. However, this carbon neutral assumption is increasingly being questioned, with several studies indicating that it may result in accounting errors and biased decision-making. To address this growing issue, we use a carbon budget model combined with an energy system model. We show that including forest sequestration in the energy system model alleviates the decarbonization effort. We discuss how a forest management strategy with a high sequestration capacity reduces the need for expensive negative emission technologies. This study indicates the necessity of establishing the most promising forest management strategy before investing in bioenergy with carbon capture and storage. Finally, we describe how a carbon neutrality assumption may lead to biased decision-making because it allows the model to use more biomass without being constrained by biogenic CO2 emissions. The risk of biased decision-making is higher for regions that have lower forest coverage, since available forest sequestration cannot sink biogenic emissions in the short term, and importing bioenergy could worsen the situation.

<p>Net-zero emission targets require transitioning to low carbon energy sources (including bioenergy) and large-scale carbon dioxide removal. Aside from direct air capture (DAC), bioenergy with carbon capture and storage (BECCS) and terrestrial carbon removal and sequestration are two available negative emission technologies (NETs) ready for large-scale deployment. Nationally determined contributions endorse bioenergy as an alternative carbon neutral energy source for fossil fuels. However, this carbon neutral assumption is disputed with several studies indicating that it may lead to accounting errors and biased decision-making.</p> <p>Bottom-up techno-economic energy system models such as the TIMES framework are used to identify and analyze potential decarbonization pathways for countries or regions. However, these models do not include biogenic carbon flows. Biogenic carbon refers to the carbon contained in biomass. One could assume that biogenic carbon is neutral since the amount of carbon emitted into the atmosphere through biomass combustion and the amount of carbon sequestered by plants during their lifetimes are equal. This assumption may be acceptable when the biomass rotation length is short, as in annual crops, and the balance between emissions and uptakes is indeed neutral. The assumption, however, may not remain valid when the sequestration period is lengthy, as in the case of forest trees. This study combines an aspatial, stand- and landscape-level modeling framework (CBM-CFS3) with a bottom-up techno-economic energy system model (NATEM). We use the CBM-CFS3 output to model various forest management strategies that would result in different biomass availability for bioenergy as well as net forest carbon stocks and emissions. This allows us to determine whether and how this biomass will be used in the energy system over time. Besides, we model several forest-based bioenergy and BECCS technologies to allow the energy system to use the available biomass. This is the first time biogenic CO<sub>2</sub> flows are being modeled in a thorough energy system model such as TIMES. We show how the assumption of carbon neutrality results in biased decision-making (using different sets of NETs and resources). We demonstrate that the decarbonization effort could be reduced by integrating forest sequestration into the energy system model. We explore how a high sequestration capacity forest management strategy may minimize the need for expensive NETs such as DAC. Moreover, this research highlights the need to adopt the most promising forest management strategy before investing in BECCS.</p>