Should forests be used? Consequential analysis of the utilization potential of Japan’s forests considering regional long-term carbon dynamics

• Active logging with reforestation reduces carbon emissions in productive forests. • Forest conservation offers higher short-term carbon sequestration than logging. • Regional productivity significantly impacts forestry carbon sequestration outcomes. • Long-term analyses reveal the role of plantation forests in defossilization strategies. • Integrated forest management enhances climate resilience and resource efficiency. Forest management faces a persistent trade-off between conserving forest carbon stocks and harvesting wood to deliver materials and energy that may avoid fossil-intensive alternatives. This study quantifies the time-dependent life-cycle greenhouse gas (LC-GHG) consequences of two contrasting strategies for Japan’s planted forests: (i) harvesting with reforestation (harvest-and-replant) and (ii) no-harvest management. We conducted a 200-year consequential life-cycle assessment with system expansion, tracking annual and cumulative LC-GHG emissions. Forest growth and harvesting outputs were simulated using a Japan-specific yield-table-based model, and wood was allocated to two utilization pathways: long-life construction products with cascade energy recovery of residues, and direct energy use. We evaluated 36 scenarios combining forest strategy, site productivity (high/middle/low), utilization pathway, and three stylized defossilization pathways (Ambitious/Middle/BAU) referenced to SSP narratives. For construction use, harvesting becomes climate-favorable after the first rotation, and the mitigation gap increases from approximately 0.14 kt-CO2eq/ha at t = 50 to 1.93 kt-CO2eq/ha at t = 200 under high productivity. For energy use, harvesting can be emission-increasing in the near term ( t = 50) but becomes favorable over time, reaching up to 0.87 kt-CO2eq/ha lower LC-GHG emissions by t = 200. Overall, climate benefits depend strongly on the time horizon, end-use choice, and site productivity, while sustained replanting is a prerequisite for realizing long-term mitigation. The results support region-specific strategies that prioritize material use on productive sites and consider longer rotations or conservation on low-productivity sites under near-term policy horizons.