Abstract
Consequential life cycle assessment was applied to forestry systems to evaluate the environmental balance of expanding forestry onto marginal agricultural land to supply more timber for the built environment, accounting for land use effects and product substitution. Forestry expansion to supply timber buildings could mitigate UK greenhouse gas (GHG) emissions by 2.4 Gg CO2 eq. per ha of forest over 100 years, though net mitigation could be halved if beef production were displaced to Brazil. Forest thinning increases wood yields and percentage conversion of harvested wood to construction sawnwood, resulting in 5% greater net GHG mitigation compared with unthinned systems. Optimising the environmental sustainability of construction timber value chains in a circular, bio-based economy will require holistic accounting of land use (change), forestry management and complex flows of wood.
Highlights
Consequential life cycle assessment was applied to forestry systems to evaluate the environmental balance of expanding forestry onto marginal agricultural land to supply more timber for the built environment, accounting for land use effects and product substitution
Forest thinning increases wood yields and percentage conversion of harvested wood to construction sawnwood, resulting in 5% greater net greenhouse gas (GHG) mitigation compared with unthinned systems
2.3Impact assessment and interpretation Two environmental impact categories were considered in this study: global warming potential (GWP), expressed as kg CO2 eq; fossil resource depletion potential (FRDP), expressed in MJ
Summary
2.1Scope and boundary definition Given the significant GHG mitigation potential of wood use as construction material and for bioenergy through substitution of mineral building materials and FFs, respectively, as well as the potential impact of direct and indirect land use change (LUC), we applied a consequential LCA approach (Weidema, Ekvall, & Heijungs, 2009) (Figure 1) to evaluate environmental impact. In the absence of high quality data on direct product substitution ratios, preliminary estimates of the burdens avoided through substitution of mineral construction materials were made by first translating the final mass of construction timber per ha (129 and 150 tonnes per ha (20% moisture), for unthinned and thinned forests, respectively) into an equivalent area of timber-framed wall using industry standard design (0.0175 m3 of timber per 1 m2 wall). FRDP is fossil resource depletion potential and GWP is global warming potential
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