The only independent, multi-stakeholder study of the carbon impacts of burning trees to generate electricity found that it would take 40 years of forest regrowth just to get to parity in carbon pollution with burning coal for those same four decades. To get to parity with natural gas would take almost a century.
Massachusetts is redefining eligibility for renewable energy credits in response to the Manomet study. Most other states and the US EPA act as though Manomet never happened. But the findings are not controversial or revolutionary to independent scientists. They are just inconvenient for the biomass industry and electric utilities vying for green energy brownie points and millions in tax breaks and subsidies that accrue because biomass power is (wrongly) classified as renewable and carbon neutral. See a review of why the Manomet Study probably understated the carbon emissions from biomass power, here.