## 3 Results and Discussion
### Economic Benefits  
Based on wood value alone, black spruce regeneration was not economically attractive across the study area under our baseline assumptions (Figure 5, Table 2). At the optimal economic harvest ages, the average net present values for CanESM2 in the northwestern, northeastern, and southern regions of the study were \(-\$136\), \(-\$265\), and \(-\$51\) ha\({}^{-1}\), respectively. Similarly, NPVs for these regions using MIROC were \(-\$137\), \(-\$269\), and \(-\$39\) ha\({}^{-1}\); and using MPI were \(-\$226\), \(-\$263\), and \(-\$90\) ha\({}^{-1}\), respectively. The optimal harvest ages for CanESM2, MIROC, and MPI were \(39\), \(38\), and \(38\) years, respectively, for the baseline scenario. These rotation ages are well below the traditional rotation ages for this species, which are typically determined using the maximum sustained yield (MSY) approach. This disparity reflects the fact that the time value of money is not considered in the MSY approach, only biophysical yields (see discussion in [PERSON] et al. [57]). Interestingly, despite the decline in projected NPP in the second half of the century by the MIROC model (see Figure 3) both optimal harvest age and NPV did not vary much from the other two GCMs. This is due to the discount rate, which reduces  
Figure 4: Spatial distribution of gross merchantable wood volume (m\({}^{3}\).ha\({}^{-1}\)) projections modified by (a) CanESM2-; (b) MIROC-; and (c) MPI-simulated annual Net Primary Productivity (NPP) ratio (see text for details).  
the impact of the NPP modifiers--particularly toward the end of the century when the modifiers are the largest.  
Figure 5: Spatial distribution of Net Present Values (NPVs) based on wood value only for the (**a**) CanESM2; (**b**) MIROC; and (**c**) MPI models.  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Model**} & \multirow{2}{*}{**Scenario**} & \multirow{2}{*}{**OHA \({}^{\ast}\)**} & \multicolumn{6}{c}{**Northwest Ontario**} & \multicolumn{6}{c}{**Northeast Ontario**} & \multicolumn{6}{c}{**Southern Ontario**} \\ \cline{3-14}  & & & **Mean** & **Max.** & **Min.** & **Std.** & **Mean** & **Max.** & **Min.** & **Std.** & **Mean** & **Max.** & **Min.** & **Std.** \\ \hline \multirow{2}{*}{Can-ESEM} & \(W\)* & 2049 & \(-136\) & 33 & \(-221\) & 99 & \(-265\) & \(-220\) & \(-300\) & 33 & \(-51\) & 29 & \(-128\) & 67 \\  & \(W\)+ C* & 2052 & 430 & 503 & 345 & 100 & 305 & 347 & 272 & 31 & 522 & 607 & 445 & 70 \\ \hline \multirow{2}{*}{MIROC} & \(W\) & 2048 & \(-137\) & 38 & \(-228\) & 103 & \(-269\) & \(-226\) & \(-307\) & 33 & \(-39\) & 18 & \(-130\) & 68 \\  & \(W\)+ C & 2054 & 424 & 592 & 337 & 96 & 304 & 345 & 274 & 29 & 471 & 600 & 443 & 68 \\ \hline \multiWhen wood and carbon values were considered, NPVs were positive across the study area (Figure 6; Table 2). Average NPVs at their optimal harvest age for the baseline scenario for CanESM2 in northwestern, northeastern, and southern Ontario were $430, $305, and $522 ha\({}^{-1}\), respectively. NPVs for these regions using MIROC were $424, $304, and $529 ha\({}^{-1}\), respectively, and using MPI were $341, $306, and $485 ha\({}^{-1}\), respectively. A price of $5 ton\({}^{-1}\) CO\({}_{2}\) appears to be a minimum threshold at which black spruce regeneration investments start to become attractive (see also [PERSON] et al. [8]). This suggests that the overall investment results rely heavily on the carbon price assumptions/expectations. We note the maps should only be used as general indicators of relative potential value due to the coarse scale of the spatial model inputs used in the study. Optimal harvest ages ranged from 42-44 years for the three GCMs, which were slightly longer than those identified in the wood-only analysis. In comparison, [PERSON] et al. [8] reported an optimal rotation age of 49 years for coniferous forests in eastern Canada inclusive of carbon benefits.