## 4 Results
### CO\({}_{2}\) Sequestration Estimates and Errors  
#### 4.4.1 CO\({}_{2}\) Estimates and Potential Errors  
The total CO\({}_{2}\) from the forests of Japan has been calculated by taking into consideration both forest type and tree age. It should be understood that determining the accuracy of this result is quite difficult, because there is no known \"true value\" for this information. It is also necessary to note that there are always sources of error when attempting to calculate such estimations. Possible errors that could generate inaccuracies in the results have been identified and listed here:  
1. Accuracy of the land cover map (forest cover map)
2. Dependency on the backscattering model for stem volume estimation
3. Stem volume-age relationship curve
4. The sequestration value itself  
Number 1 refers simply to errors resulting from the misclassification of each forest type. As acknowledged in the work, the total area size of a forest type is an important factor in calculating total CO\({}_{2}\) sequestration, because the sequestration value per unit area is multiplied by the total area of each forest type. Figure 15 illustrates the relationship between accuracy and errors for each forest type in reference to the error matrix (Table 2). Figure 14: CO\({}_{2}\) sequestration map of Japan. The figure shows the relationship between the classes used in the classification scheme. It indicates the accuracy (percentage value inside the triangle) and errors of omission (outside the triangle). The arrows indicate the misclassification of the classes that might have been classified into one class (beginning of the arrow) but may have instead been classified into a different class (end of the arrow). For example, coniferous forests may have had an 85% accuracy rate in classification, while 4% were misclassified into evergreen broadleaf, and 6% were misclassified into deciduous broadleaf forests. The same can be said for the other two classes. Thus, an 85% accuracy rate for coniferous may be true, but there are 4% and 6% chances of errors due to misclassification into evergreen and deciduous broadleaf forests, respectively, in calculating the total CO\({}_{2}\) amount. The same can be shown for the other classes, mutatis mutandis. The evergreen broadleaf class shows 20% and 25% chances of error from deciduous broadleaf and coniferous forests, respectively, while deciduous broadleaf shows 11% and 15% chances of error from evergreen broadleaf and coniferous forests, respectively. For number 2, errors in the backscattering model can be explained by the RMSE calculated from the estimated stem volume _versus_ the ground truth volume information (Figure 4). As has been explained in an earlier section, the RMSE of the backscattering model resulted in 105.58 m\({}^{3}\)/ha. This can lead to errors in transforming the stem volume into the tree age information, and thus become an error in the estimation of CO\({}_{2}\) sequestration. For example, in the coniferous trees in high growth rate areas, a 100 m\({}^{3}\)/ha difference can miss the true tree age by \(\div\)6 years. Larger differences accrue to lower growth rate areas, for example at Site 3 (low growth rate region) 100 m\({}^{3}\)/ha can miss the tree age by \(\div\)13 years by looking at the stem volume-age relationship data from the Oita Prefectural Government. A 6-year difference might change the estimation values; for example, the forested coniferous areas at peak ages could be classified to earlier or older age ranges and vice versa: the older age classes could change to the peak tree age classes. Therefore, this error source must be acknowledged as one possible error in the estimation. For number 3, the tree age transformation used the reference data provided by the Oita Prefectural Government and from [PERSON] _et al._[41]. According to this growth curve, the stem volume information was reclassified for the whole of Japan. The issue here is whether this growth curve also has implications for other regions in Japan.