Life Cycle Assessment (LCA) is a technique used for decision-making support to assess the environmental impact of product systems through its life cycle (ISO 14040 2006) in a diverse range of fields (Curran 2012). Nevertheless, the effective use of LCA is challenged by the suitability of the methods used and the exactness of the modelling assumptions. Due to the increasing attention towards mitigation and adaptation to climate change impact, LCA is extensively used for assessing the environmental impact of forestry products (Brandão, Milà i Canals, and Clift 2011; Rex and Baumann 2007; Werner and Richter 2007; Wessman, Hohenthal, and Kaila 2003). However the inclusion of forest carbon (C) cycle in LCA is not straightforward (Helin et al. 2012; Kløverpris and Mueller 2012). This study explores the suitability of different existing LCA methodological approaches accounting for direct and indirect impacts related to forestry and forest carbon cycles. The research evaluates the indirect Land Use Change (iLUC) impact on forestry and the time accounting of CO2 emission/uptake of forest biomass.
Forests play a key dual role, both sequestering C from the atmosphere (IPCC 2007) and emitting C due to forest degradation for some years after harvesting or thinning (Mäkipää et al. 1999, 1490-1501) and to products by hastening land-use changes and deforestation. In LCA, biomass from sustainably grown forests tends to be considered C neutral as the C released during combustion, is assumed to be re-sequestered in the growing biomass (Cherubini et al. 2011). Nevertheless C neutrality does not mean that the process implies climate neutrality: if during the time in between C release and sequestration, the C stays in the atmosphere, a warming effect is achieved and the impact can be remarkable. However, whether and how much C is released in the atmosphere, depends on the use of the biomass and its source: if used for long-lived products, if used for substitution of other materials (fossil fuels, construction material) or if a change in the forest C stock occurs (harvesting of stems, branches, roots, litter, soil), and the time considered for the biomass re-growth. The study compares ten LCA methodological approaches to model the following aspects: land use change effects, time horizon, climate indicator for impact assessment and forest C stock. This is done applying different approaches to the same case study to ensure comparability. The selected functional unit was the production of 1m3 of spruce as a construction material in Götaland, Sweden, due to the relevance timber is re-gaining as a sustainable construction material (Smith and Snow 2008).
The obtained results are confronted in order to assess strengths and weaknesses of the considered methodologies. The outcome underlines a substantial difference in results and modelling uncertainties, rising further methods issue and standardization requirements for accounting C cycle in LCA.