The unique generation, landownership, and resource attributes of the southeastern United States make the region an important test bed for implementation of novel renewable energy policy interventions. This study evaluates the environmental and economic implications of one such intervention, a hypothetical region-wide renewable portfolio standard (RPS) with biomass carve-outs. It utilizes the Forest and Agriculture Sector Optimization Model with Greenhouse Gases (FASOMGHG) to assess the multi-sector and interregional allocation of forest harvest activity, and then uses the Sub-Regional Timber Supply (SRTS) model to assess intraregional variation in forest composition and greenhouse gas (GHG) mitigation potential. The analysis finds that existing resource conditions influence the regional distribution of land use and harvest changes, resulting in a spatially and temporally diverse forest carbon response. Net forest carbon in the Southeast is greater in the RPS Scenario than in the No RPS Scenario in all but the final years of the model run. Accounting for displaced fossil emissions yields net GHG reductions in all time periods. Both research methodology and findings are also applicable to a broader suite of domestic and international policies, including European Union renewable energy initiatives and GHG mitigation under Section 111 of the U.S. Clean Air Act.