Evaluating carbon balance of wood cascading – the need for accounting storage period and rate of carbon uptake

The renewed interest in wood has driven growth in its demand. Although a renewable resource, wood supply is limited by the forest growth rate and sustainable forest management practices. Using waste wood (sawmill residues and post-consumer waste) in cascading is essential to meet this growing demand without exerting additional pressure on the forests. Cascading is the sequential use of resources as long, as many times and as efficiently as possible for material applications and recover energy from them when no material use is feasible. Several studies have evaluated the environmental impact of cascading systems using LCA. However, these studies mainly focused on the cascade (benefit of using waste instead of fresh wood for producing a product) and substitution effect (substituting wood for fossil- or mineral-based materials). Wood cascading contributes also by storing the carbon in harvest wood products (HWP) for longer and gives the forests that were cleared for wood harvesting sufficient time to regrow and sequester the equivalent amount of carbon initially harvested from the forests. Long-life cascades have a comparatively lower global warming potential (GWP) because the embedded carbon emitted at the end of the storage period spends less time in the atmosphere (within the considered time horizon). While the GWP of short life cascades could be positive and the biomass may need to be stored in the HWP for a certain duration for the system to be carbon-neutral. The longer the storage period, the higher is the climate benefit. Plus, biomass from a fast-growing forest leads to a lower GWP because the carbon is sequestered more rapidly. These temporal aspects (time of carbon storage in a cascade and the rate of carbon uptake) affect the GWP of cascading systems - an aspect currently overlooked in LCA studies. Please click Additional Files below to see the full abstract