20 years of life cycle assessment (LCA) in the forestry sector: state of the art and a methodical proposal for the LCA of forest production

Life cycle assessment (LCA) techniques have been developed since the late 1960s in order to analyze environmental impacts of various products or companies. Although LCA techniques of forest production have been already conducted since the early 1990s, consistent and comprehensive LCA studies are still lacking for the forestry sector. In order to support better comparability between LCA studies, we analyzed the problems and differences by conducting a descriptive and quantitative analysis of existing LCA studies of forest production with special focus on Global Warming Potential (GWP). We analyzed 22 different peer-reviewed studies, four original reports and two databases. Important issues were, among others, the goal of the studies, system boundaries, functional units, impact categories and involved processes. In addition, a quantitative analysis was purchased where the results of the GWP of the reviewed studies were analyzed. The studies showed large differences between methodical assumptions and their subsequent results. For the GWP, we found a range of 2.4-59.6 kg CO2-equiv.*m(-3) over bark (ob; median = 11.8; n = 41) from site preparation to forest road and 6.3-67.1 kg CO2-equiv.*m(-3) ob (median = 17.0; n = 36) from site preparation to plant gate or consumer. Results varied as a function of the included processes and decisive assumptions, e.g., regarding productivity rates or fuel consumption of machineries. Raw wood products are widely declared as "carbon neutral," but the above-mentioned results show that absolute carbon neutrality is incorrect, although the GWP is low compared with the carbon storage of the raw wood product (range of C-emitted/C-stored in wood is 0.008-0.09 from forest to plant gate or consumer). Thereby, raw wood products can be described as "low emission raw materials" if long-term in situ carbon losses by changed forest management or negative direct or indirect land use change effects (LUC, iLUC) can be excluded. In order to realize improved comparisons between LCA studies in the forestry sector in the future, we propose some methodical approaches regarding the harmonization of system boundaries, functional units, considered processes, and allocation assumptions. These proposals could help to specify the description of the forest production outlined in existing Product Category Rules for Environmental Product Declarations (e.g., EN ISO 16485 2014 or EN ISO 15804 2012) following EN ISO 14025 (2011) and for carbon footprinting standards like the Publicly Available Specification (PAS) 2050 (2011) or the European Environmental Footprinting Initiative.