SignificanceAfforestation and reforestation (AR) are nature-based solutions to climate change. However, the greenhouse gas (GHG) mitigation efficacy of protection or commercial AR is under debate. This study develops a dynamic life cycle assessment to quantify the GHG mitigation potential of protection and commercial AR on marginal land in the southeastern United States. We found that commercial AR with cross-laminated timber and biochar production generally mitigates more GHGs across 100 y than protection AR and commercial AR with traditional lumber production. Protection AR could mitigates more GHGs in a shorter timeframe (≤50 y). These results highlight the role of synergizing protection AR, innovative wood utilization, and strategic forest plantation management in supporting short- and long-term climate change mitigation goals.