GHG displacement factors of harvested wood products: the myth of substitution

Background A commonly held idea is that substituting wood for fossil fuels and energy intensive materials is a better strategy in mitigating climate change than storing more carbon in forests. This opinion, although ratified by the forest and energy policies of many countries, especially in Europe, remains highly questionable for at least two reasons. Results Firstly, the carbon footprints of wood-products are underestimated as far as the “carbon neutrality” assumption is involved in their life cycle analysis, as it is most often the case. As a matter of fact, when taking into account the forest carbon dynamics consecutive to wood harvest and the limited lifetime of products, these carbon footprints are time-dependant and their presumed values under the carbon neutrality assumption are achieved only in steady-state conditions. For time horizons comparable with the climatic deadlines, the values to apply may be of the same order as the carbon mass in the harvested wood from which the products originate. Secondly, even if carbon footprints are correctly estimated, the benefit of substitutions is overestimated when all or part of the wood products are supposed to replace non-wood products whatever the market conditions. Indeed, substitutions can be considered as effective only if an increase in wood harvesting implies verifiably a global reduction in production of non-wood products. Conclusions Most studies that advocate energy or material substitutions lack rigour to these respects and incite the increase in wood harvesting. Such an increase impedes forest carbon storage and could be counter-productive for climate change mitigation objectives.