关键词: 森林, 林产品, 碳减排, 物质流, 生命周期

Abstract:

Objective: Worldwide studies on pathways of post-harvest carbon emission reduction in recent 30 years are reviewed to provide a theoretical basis for China-specific studies and the utilization of post-harvest carbon emission reduction to improve forestry's capacity to mitigate climate change. Method: We summarized major pathways of post-harvest carbon emission reduction worldwide and analyzed the life-cycle material flow and substitution categories of harvested wood products (HWP), the backbone of post-harvest carbon emission reduction, in 24 and 15 countries/regions, respectively. We also investigated the country-specific features in life-cycle material flows and summarized the displacement factors of major substitution categories in the above-mentioned countries. Furthermore, we provided a prospect of possible future research needs based on the literature review. Result: First, the studies in recent 30 years reported three major pathways of post-harvest carbon emission reduction, including HWP carbon storage, HWP substation benefit, and the optimized forest management considering both pre- and post-harvest carbon emission reduction. Among them, the HWP substitution benefit has been a frontier of the relevant research fields and provided new insights in forest management considering pre- and post-harvest carbon emission reduction. Second, the studies in developed countries have comprehensively analyzed domestic life-cycle material flows whereas the studies in developing countries were relatively weak, and very few modeling analyses based on the Tier-3 method recommended by the Intergovernmental Panel on Climate Change (IPCC) are available. We also found that the material flows driven by international trade are a common research gap in the studies in all these countries, which undermines the linkage of the countries involved in an HWP life cycle and restricts effective policy design to improve carbon emission reduction potential of global forestry. Third, the HWP substitution studies, which are mainly in European countries, reported that the five major substitution categories, namely, substitution in construction, energy, furniture, other products, and the material substitution without dividing specific end uses, have an average displacement factor of 1.32 t·t^-1 (n=50), 0.70 t·t^-1 (n=40), 1.03 t·t^-1 (n=21), 1.13 t·t^-1 (n=8), and 1.13 t·t^-1 (n=37), respectively. However, the displacement factors differ significantly among studies and countries. Conclusion: First, as the major developing country and the largest HWP producing and consuming countries in the world, China should improve existing IPCC Tier-2 method-based life-cycle material modeling and analysis to an IPCC Tier-3 method-based one to provide a high-quality example for other developing countries. Second, the analysis of international material flow is an important future research need, providing an opportunity for China, the largest HWP exporting and importing country in the world. Lastly, there is still large research potential in the field of HWP substitution benefit. Especially, the highly subjective fundamental assumptions and substitution scenarios have led to unreliable displacement factors, which has large room for improvement.

Key words: forest, harvested wood products, greenhouse gas mitigation, material flow, life cycle