## 4 Results
### CO\({}_{2}\) Sequestration  
#### 4.3.1 CO\({}_{2}\) Sequestration by Forest Types and Ages  
The stem volume-age relationship data were modified from the original Oita data [5] to compute high, moderate and low growth curves for coniferous and deciduous broadleaf forests (Figure 8), which were used in turn to convert the so-obtained stem volume map (Figure 6) into tree age classes. Figure 9 shows the analysis between annual precipitation and tree growth for coniferous and deciduous broadleaf forests. The results show a clear trend in the relationship between precipitation and tree growth. For the sugi trees (coniferous), increasing precipitation results in larger tree growth. On the other hand, for the sawtooth oak (deciduous broadleaf), the opposite trend can be observed, where tree growth increases with decreasing precipitation. The negative trends in the deciduous broadleaf forests might be caused by the precipitation data used. The precipitation data are an annual value, which means that it was not taken into account during the time when deciduous trees are likely to be photosynthesizing. If the precipitation falls mostly in the fall or winter, the trees may not be able to take advantage of it and thus would have lower \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & \multirow{2}{*}{**KIA = 0.65**} & \multicolumn{6}{c}{**Reference**} \\ \cline{3-8}  & & **Coniferous** & **Evergreen** & **Deciduous** & & & \\  & & **Broadleaf** & **Broadleaf** & **Othes** & **Total** & **ErrorC** \\ \hline \multirow{4}{*}{**Condes**} & Coniferous & **852** & 253 & 149 & 24 & 1278 & 0.3334 \\  & Evergreen & & 41 & **533** & 113 & 30 & 717 & 0.2566 \\  & Broadleaf & & & & & & \\  & Deciduous & & & & & & \\  & Broadleaf & 59 & 200 & **680** & 54 & 993 & 0.3152 \\  & Others & 48 & 14 & 58 & **892** & 1012 & 0.1186 \\ \hline \multirow{4}{*}{**Condes**} & Total & 1000 & 1000 & 1000 & 1000 & 4000 & \\  & ErrorO & 0.1480 & 0.4670 & 0.3200 & 0.1080 & & 0.2607 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Error Matrix showing the reference data (ground truth) _versus_ the image classification. Overall accuracy shows approximately 74% and Kappa Index of Agreement (KIA) as 0.65. Figure 8: Mean growth curve of (**a**) coniferous and (**b**) deciduous broadleaf forests in each growth rate region, computed from the original Oita data. Figure 10: Precipitation data classified using the threshold values for evaluating the growth rate of (**a**) coniferous forests and (**b**) deciduous broadleaf forests. Figure 9: Relationship analysis between annual precipitation and tree growth for (**a**) sugi (cedar) trees and (**b**) kunugi (sawtooth oak) trees. The distribution of the precipitation classes and the thresholds is seen in Figure 10. For the coniferous forests, Class 1 is the area with a low growth rate, Class 2 is moderate, and Class 3 is a high growth rate. For deciduous broadleaf forests, Class 1 is high growth rate, Class 2 moderate, and Class 3 is low growth rate. Finally, Figure 11 shows a graph of the distribution of tree age overlaid with the forest cover data to extract the exact forest types. For the coniferous and deciduous broadleaf forests, the growth rates are considered for the age conversion, however for the evergreen broadleaf it was not, due to the lack of reference data, so that has been converted directly from the stem volume map using the stem volume-age relationship information provided by [PERSON] _et al._[41]. The statistical distribution of forest tree ages can be seen in Figure 12. Coniferous forests can be widely distributed among the different tree ages. The majority lie in the 25-30 year age range for Site 1 (high growth rate regions), 30-35 years range for Site 2 (moderate growth rate regions) and 35-40 years range for Site 3 (low growth rate regions).