Forest biomass can be used in two different ways to limit the growth of the atmospheric greenhouse gas (GHG) concentrations: (1) to provide negative emissions through sequestration of carbon into forests and harvested wood products or (2) to avoid GHG emissions through substitution of non-renewable raw materials with wood. We study the trade-offs and synergies between these strategies using three different Finnish national-level forest scenarios between 2015 and 2044 as examples. We demonstrate how GHG emissions change when wood harvest rates are increased. We take into account CO₂ and other greenhouse gas flows in the forest, the decay rate of harvested wood products and fossil-based CO₂ emissions that can be avoided by substituting alternative materials with wood derived from increased harvests. We considered uncertainties of key parameters by using stochastic simulation. According to our results, an increase in harvest rates in Finland increased the total net GHG flow to the atmosphere virtually certainly or very likely, given the uncertainties and time frame considered. This was because the increased biomass-based CO₂ and other greenhouse gas emissions to the atmosphere together with decreased carbon sequestration into the forest were very likely higher than the avoided fossil-based CO₂ emissions. The reverse of this conclusion would require that compared to what was studied in this paper, the share of long-living wood products in the product mix would be higher, carbon dioxide from bioenergy production would be captured and stored, and reduction in forest carbon equivalent net sink due to wood harvesting would be minimized.

Fossil‐based emissions can be avoided by using wood in place of non‐renewable raw materials as energy and materials. However, wood harvest influences forest carbon stocks. Increased harvest may reduce the overall climate benefit of wood use significantly, but is widely overlooked. We reviewed selected simulation studies and compared differences in forest carbon and amount of wood harvested between harvest scenarios of different intensities for three different time perspectives: short‐ (1–30 years), mid‐ (31–70 years), and long‐term (71–100 years). Out of more than 450 reviewed studies 45 provided adequate data. Our results show that increased harvest reduces carbon stocks over 100 years in temperate and boreal forests by about 1.6 (stdev 0.9) t_C per t_C harvested (referred to as carbon balance indicator (CBI)). CBI proved to be robust when outliers explicitly influenced by factors other than changes in the harvest rate, such as fertilization or increase in forest area, were removed. The carbon impacts tend to be greatest in the mid‐term, but no significant difference in was found for average values between short and long time‐horizons. CBI can be interpreted as carbon opportunity costs of wood harvest in forests. Our results indicate that even after 100 years, CBI is significant compared to the typical GHG credits expected in the technosphere by avoiding fossil emissions in substitution and increasing carbon stocks in harvested wood products. Our estimates provide typical values that can directly be included in GHG balances of products or assessments of mitigation policies and measures related to wood use. However, more systematic scenarios with transparent information on influencing factors for forest carbon stocks are required to provide better constrained estimates for specific forest types.

Wood use generates technosphere carbon credits (TCCs) through avoided fossil‐based emissions and net sequestration of carbon into the technosphere (harvested wood products and geological storage). We investigated how large and uncertain TCCs of wood use per carbon harvested are considering the current and alternative ways of using wood, and the effects of the decarbonization of societies over 25‐, 50‐, and 100‐year time horizons. We applied stochastic simulation and scenario analysis using Finnish market structure as a baseline to demonstrate the use of the TCC calculator created. The mean value of TCCs of wood use were between 0.2 and 0.5 t_C/t_C with an uncertainty range from 0.1 to 0.8 t_C/t_C, depending on the scenario. The uncertainties were mainly concerned with the extent to which (1) fossil‐based emissions are avoided through substitution (displacement factors) and (2) fossil‐based raw materials are substituted (substitution rates). Assumptions on the decarbonization of societies reduced TCCs of wood use significantly over time. TCCs of wood use can be increased by directing wood into uses that substitute fossil‐intensive materials and have a long lifetime, such as construction materials, and increasing energy recovery and avoiding emitting carbon at the end of life of harvested wood products by carbon capture and storage. However, they were very likely to be considerably lower than forest carbon debits resulting from harvesting additional wood for substitution under all considered circumstances and under a wide but reasonable range of stochastic parameter values. Thus, the result emphasizes the need to reduce overall consumption of goods to mitigate climate change.

Purpose: Carbon and biodiversity footprints are increasingly calculated. However, little attention has been paid to the coherency of methodological choices and interpretation of the footprint results. This paper aims to clarify the coherency between the choice of reference land use and carbon and biodiversity footprints and discuss the challenges encountered. Methods: First, we analyse features of reference land use options proposed in ISO 14067 (2018) i.e. business as usual, projected future, target, potential natural regeneration and historic baseline. Second, we discuss the connection between temporal scope and life cycle of land use. Third, we provide guidance on how to choose reference land use coherently. Fourth, we discuss specific issues related to carbon and biodiversity footprints and their relationship to reference land use. Finally, we provide conclusions and recommendations for further conceptual development. Results and discussion: Choice of reference land use and determination of temporal scope of a study may significantly influence the assessment of carbon or biodiversity footprints. If the aim of a footprint study is to assess the effects of land use, reference land use should describe dynamically non-use of land. Thus, potential natural regeneration or continuation of natural state (if it is the starting point) of land is the coherent reference land use in this case. If the aim of a footprint study is to assess the effects of a decision to change land use or its management, reference land use should describe dynamically alternative use of land expected without the studied decision. Business as usual or projected future is a coherent reference land use in this case. Historic baseline or target reference land use may be useful in comparing the ecosystem value of the studied land use with a pre-set historic baseline or (policy) target. Conclusions: We conclude that coherent choice of reference land use for carbon or biodiversity footprints depends on the goal and scope of a study. Beyond methodological coherency, issues related to the reliability and availability of appropriate data are relevant and vary between reference land use choices. However, difficulties in the assessment should not justify incoherent choices. We recommend that uncertainties are not overlooked but incorporated in the assessment and considered in the interpretation of the results. In addition, we recommend that key methodological choices, including the definition of the purpose of a study, chosen temporal scope and applied reference land use, should be clearly and transparently presented.