The Climate Stewardship Act, a global warming mitigation policy calling for a cap-and-trade program, was reintroduced in the United States Senate this year. The Energy Information Administration analyzed the implications of the bill and found that under such a policy renewable energy will increase, with the strongest response coming from biomass energy. Dedicated energy crops are one source of biomass that is expected to contribute significantly to the future biomass energy supply. This paper describes a system dynamics model of the carbon impacts from a dedicated energy crop. The work relies on another carbon accounting model, GORCAM, which uses spreadsheet modeling to investigate various land management regimes. We were able to reproduce the GORCAM results for a 20-year harvest rotation; we then simulated several different harvesting intervals to gain insight into the carbon impacts of these rotations. Our results show that a shorter harvest rotation will remove more carbon from the atmosphere if the biomass is used to replace a fossil-fuel burning power plant compared with no-harvest or longer harvest scenarios. These results agree with previous work that found long-term benefits were greater for scenarios where trees were planted for energy generation rather than specifically for carbon sequestration.