**5. Conclusions**

Strong demand for oil in the United States (U.S.) for the transportation sector, multiple societal issues, including climate change concerns, heavy air pollution, high dependence on imports, and a multitude of security concerns have stimulated research in finding methods to reduce the use of fossil fuels for transportation fuel by substituting with renewable biomass. However, there is a lack of comprehensive regional estimates of available biomass, hindering the opportunity to maximise benefits. Using the State of Michigan in the United States as a case study, the long term harvest probabilities of timber were evaluated based on historic harvest data, as well as the implications of collecting residues

and their use for ethanol production. The emission benefits of replacing fossil fuel with ethanol were also evaluated. Uncertainties that are considered include harvest solutions, harvest types, transportation distances of biomass/biofuel, biomass conversion technologies, and higher heating values, etc. The results indicate that the study region has the potential to supply 0.75–1.4 Mt dry timber annually and less than 0.05 Mt of dry residue produced from these harvests. This amount of forest biomass could generate 0.15–1.01 Mt of ethanol, which contains 0.68–17.32 GJ of energy. The substitution of ethanol for gasoline as transportation fuel has potential to reduce GHG emissions by 0.043–1.09 Mt CO2eq annually. In addition to promoting energy security and reducing GHG emissions, the use of forest residues for energy would create additional income and employment opportunities in the forest based sector.

**Acknowledgments:** This research was supported by National Science Foundation of China (No. 71502173). This research acknowledges the financial support provided by National Key Research and Development Program of China (No. 2016YFC0802103), National Science Foundation of China (No. 51504274), and the Program for New Century Excellent Talents in University (No. NCET-13-1028). The Project-sponsored by SRF for ROCS, SEM.

**Author Contributions:** Fengli Zhang developed the research method, conducted the case analysis and wrote the paper. The rest of the authors helped collect the data and improve the wording of the paper.

**Conflicts of Interest:** The authors declare no conflict of interest.
