This article analyzes different forest management strategies to meet the increasing demand of biomass for bioenergy and assesses the resulting global warming implications. Applied to maritime pine forest plantations in Portugal, the assessed strategies are: full harvest of residues (FULL); sustainable and proactive management (SMART); expansion of forest plantations on abandoned farmland (EXP); and biomass import (IMP). A dynamic CO2 inventory was obtained for each scenario using a parametric stand-level C-flux model adapted to Portuguese conditions, which was then extended to the landscape-level and coupled to a dynamic climate model. The time-adjusted absolute global warming potential (AGWP) was then calculated at both stand and landscape levels, considering the timing of all CO2 emissions and uptakes (both fossil and biogenic). To test the robustness of the findings, a sensitivity analysis was performed. Results show that, in a supply-constrained context like Portugal, SMART and EXP management strategies can provide important global warming mitigation benefits (GWPbio < 0), although their supply-response is slow (long-term strategies). On the other hand, FULL and IMP management strategies show moderate to null AGWP reduction potential (0 < GWPbio < 1), while involving other possible risks (e.g., exacerbated soil erosion, nutrient depletion or uncertain impacts abroad), but their supply-response is fast (short-term strategies). National forest regulations and energy policies should be revised to address the drawbacks related to all management strategies and to unleash the multiple environmental benefits they can provide in the short- and long-term.