Forest products: contribution to carbon storage and climate change mitigation

Climate change is one of the biggest threats for our earth. Mitigation of climate change is thus an urgent challenge our society needs to take up. Many benefits are provided by forests, and one is their potential to mitigate climate change. This mitigating effect can be achieved in many ways, for example increasing the stock of carbon in managed forests or replacing more emission-intensive goods with wood-based products. To maximize the climate mitigation potential of forest and wood products use it is important to correctly quantify their climate mitigating role. A tool to do so is life cycle assessment (LCA), which estimates the environmental burdens of services and goods over their entire life cycle. While this method has been widely used in the past in the forest sector, its application still poses many challenges. Here, we worked to improve the capability of LCA to be used as a tool to assess the climate mitigation potential of forests and wood products. This general context of the thesis is presented in chapter 1.

In the first part of the thesis the challenge was addressed at a more generic LCA level.

Chapter 2 focused on the collection and analysis of data on the current state of forest management practices in Europe. Based on the collected information the free and open EFO-LCI (European Forestry Operations Life Cycle Inventory) database was built. The collected data showed that European forests are quite diverse in many aspects like rotation length, amount and assortments of wood products harvested and machinery used in the interventions. This diversity in the management is also translated into different life cycle impacts. The variability of the input data proved to be an important factor in determining the variability of the Global Warming impact of raw wood production, with the estimated anthropogenic impacts ranging from 0.4 to 73.1 kg CO2eq/m3 in EFO-LCI and the biogenic impacts from 1.6 to 451.9 kg CO2eq/m3. The release of our regionalized inventory can serve to improve the accuracy of life cycle studies aiming at assessing the relative environmental role of wood production.

Chapter 3 tackled the issue from a more general methodological viewpoint. The lack of temporal resolution in LCA, and of a methodology to solve the Life Cycle Inventory (LCI) dynamically, was addressed due to the relevance of the issue for the forestry sector. Network analysis and convolution were used in combination with the traditional matrix-based structure of life cycle inventory to both solve the LCI dynamically and consider time also in the impact assessment. Following the open source philosophy, the developed approach was also translated into a free and open software named Temporalis. The functioning of the method and the advantages of using a dynamic approach were illustrated with a real-case example. The dynamic life cycle of glulam was performed to show how considering its temporal information can offer new insights into the environmental role played by wood products. If was found that the temporal parameters (i.e. rotation length and product lifetime) used to model the dynamic of biogenic carbon fluxes can greatly influence the results which, for the same system, could range from -71 kg CO2eq 443 kg CO2eq when considering a temporal horizon of 20, from -901 kg CO2eq to 667 kg CO2eq when considering a temporal horizon of 100 years and from -546 kg CO2eq  to -120 kg CO2eq when considering a temporal horizon of 500 years.

In the second part, a more applied approach was followed.

Chapter 4 combined the work of the previous two with other data and modelling approaches to assess how European forests would be affected by a change in the management strategies in terms of carbon fluxes, timber harvesting and climate change impact. It was found that timber production is a relatively efficient production chain, with an estimated GWP impact ranging from -1986 kg CO2eq/m3 harvested wood to -2989 kg CO2eq/m3 harvested wood depending on the year and the scenario. Looking at the overall performance of the system, changing management increases the climate change impact of the system at most of 11% by 2050, with this effect mostly driven by the increased emissions of soil carbon. In the study also the future wood demand was considered and this economic consideration proved to be a decisive factor in shaping the future evolution of European forests. In fact, the realizable changes in forest management were buffered by the constraint posed by the relative demand for timber.

In chapter 5 a dynamic and consequential life cycle-based assessment framework to estimate the climate mitigation potential of actions and policies in the forest-wood sector was proposed and illustrated with an example. In the analyzed case-study it has been shown that the estimated net climate change impact of the systems could range from - 274 to -111 tonnes of CO2eq/ha/yr by the year 2030 in function of the methodological approach followed. The used accounting procedure influenced the estimated substitution effect which, eventually, was secondary in comparison to the benefits yield by the reduced climate change impact of the system. The results suggested that increasing the climate efficiency of the whole chain should be prioritized over the maximization of the substitution benefits.

This work contributed to improving the quality and availability of the inventory data in the European forestry sector and provided a solution for the issue of temporal consideration in LCA, which allows dealing better with the long production cycles of the forestry-wood sector. It was also learnt that the theoretical mitigation potential of forest management might be constrained by the economy and that reducing the climate change impact of the wood sector rather than maximizing the substitution benefits might be the best climate strategy.

Future research should, among others, focus on the better understating dynamic of wood in the wood sector, for which data are still way to scarce and very little is known about how the resource wood is effectively used along the chain.