In an attempt to predict forest sustainability in the presence of bioenergy demand to replace coal, we developed a regional timber supply model for southeastern United States (US) spanning 50 years satisfying 100% of traditional demand by pulp and sawmills, both with and without replacement of coal by biomass in power plants for electricity generation. In the Baseline scenario, with only traditional demand and no coal replacement, about 1.46 million acres of forestland were harvested annually from the study area—six states in the southeastern US—Alabama, Florida, Georgia, North Carolina, South Carolina, and Tennessee. In Scenario 1, when 50% of coal was replaced with pulpwood along with satisfying 100% of demand in the mills, the annual average harvested acreage increased by 150% to 3.65 million acres. When both pulpwood and logging residues were used to replace 50% of coal along with traditional demand, in Scenario 2, harvested acreage was 80% higher compared to Baseline, about 2.63 million acres. Average age of harvested stands decreased in Scenario 1 and 2 compared to Baseline. About 1.56, 2.86, and 2.05 billion tons of timber were produced over the 50 years in Baseline, Scenario 1, and Scenario 2, respectively. Most timber came from the planted softwood stands. At least 92% of timber demand in the mills was satisfied from within the state in all scenarios. Stand carbon increased by 927 million tons in the Baseline scenario while decreased by 1,800 and 415 million tons in Scenario 1 and 2, respectively. Sensitivity analysis of various percentages of coal replaced with biomass revealed that replacing 10% of coal with pulpwood and logging residues provided the highest carbon benefit, combining changes in stand carbon and avoided carbon by replacing coal in the power plant.