**4. Discussion**

There is a vast of literature exploring the estimation methods of biomass potential. Since this study focused on timber and corresponding harvest residues instead of other types of biomass, only the literature studying forest biomass availability were examined. When compared to the volume estimation methods that are developed in this study, the 1998–1999 Silvicultural Analysis established an accounting framework and applied it to a 10-year (1999–2008) projection of the State Forest inventory in Michigan [32]. Kukrety et al. estimated the potential availability of roundwood and harvest residues using FIA inventory data and age-class progression techniques combined with average stand growth and yield models and applied it to the Lake States region [3]. To estimate potential annual yield from urban trees, it is a general method by evaluating the rate of urban trees becoming available for utilization. A vast of literature of potential wood biomass availability focused on growth rates of different vegetation type [47], while MacFarlane used mortality rate of urban trees and conducted a regional study of the potential availability of urban wood biomass in a 13-county area of Michigan [21]. Adams integrated published specific gravity and biomass distribution data with bolewood volumes predicted from regression equations relating these volumes to stand height and basal area to estimate forest biomass in northern lower Michigan [48].

As discussed above, the value for the prediction of biomass, ethanol, energy and emission savings vary depending up on regional parameters, scope of the study, assumptions made, and other factors that are considered for analysis [25]. This study predicted timber volume by collecting historical timber sales data from literature combing the time trend analyses from [31]. The energy potential was estimated based on heating value, which is a popular method for quality analysis of biomass [49]. This study conducted a comprehensive study approximating long-term forest biomass availability and associated energy production and emissions analysis to fill the gap by taking Michigan as one study region. The derived results are comparable to these studies discussed above.
