## 3 Results
### Relative Change in Recovery of the Forest  
To distinguish the effects of the meteorological conditions from the temporal changes in forest recovery, the ratios of variables (NBR\({}_{2.1}\), NBR\({}_{1.6}\), NDVI, and GPP) in July-August in the burned areas were compared with the reference area and investigated. These ratios can accurately express the process of forest recovery (Figure 6). Average values of indices in the unburned forest area were ideal criteria for indicating complete forest recovery. The ratios of NBR\({}_{2.1}\) in burned areas showed an increase after the forest fire (Figure 6a). Immediately after the forest fire, ratios of NBR\({}_{2.1}\) were 0.940, 0.875, and 0.806 in areas with low, moderate, and high fire severity, respectively. They reached the criteria level (1.0) in 2004, 2006, and 2008 in areas with low, moderate, and high fire severity, respectively (Table 3). These results were consistent with the independent two-sample \(t\)-test results. After 2008, the ratios of NBR\({}_{2.1}\) in all areas exceeded the confidence interval of the criteria level. Ratios of NBR\({}_{1.6}\) showed similar patterns to those of NBR\({}_{2.1}\). For example, ratios of NBR\({}_{2.1}\) and NBR\({}_{1.6}\) rapidly increased during the first three years after the forest fire, although the initial values and overall temporal changes were different (Figure 6b).  
NDVI ratios were 0.942, 0.867, and 0.785 in areas with low, moderate, and high fire severity in July-August 2000, respectively. The ratios increased, particularly during the first three years after the forest fire. These patterns were consistent with the ratios of NBR\({}_{2.1}\) and NBR\({}_{1.6}\). The NDVI ratios reached the confidence interval values of the criteria level in 2006 and 2009 for areas with low and moderate fire severity, respectively. After 2009, ratios of NDVI in areas with low and moderate severity levels remained between 0.97 and 1.0. However, in areas with high fire severity, the ratio of NDVI barely met the recovery level in 2017.  
Ratios of GPP showed different patterns compared to the NBR and NDVI ratios. The GPP in burned areas reached the confidence interval values of the recovery level in 2001, 2001, and 2003 for areas with all levels of fire severity. Across the whole study period (2001 to 2017), the slope of the GPP ratio in areas with low fire severity was 0.004. However, the slopes of the GPP ratios in areas with  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Indices**} & \multirow{2}{*}{**Meaning of Monitoring**} & \multicolumn{3}{c}{**Recovery-Time Point (Year)**} \\ \cline{3-5}  & & **L** & **M** & **H** \\ \hline NBR\({}_{2.1}\) & Moisture condition & 2004 & 2006 & 2008 \\ \hline NBR\({}_{1.6}\) & Moisture condition & 2006 & 2008 & 2015 \\ \hline NDVI & Vegetation biomass & 2009 & 2009 & \\ \hline GPP & photosynthetic activity & 2001 & 2001 & 2004 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Recovery-time point (year) indicated by four indices (i.e., NBR\({}_{2.1}\), NBR\({}_{1.6}\), NDVI, and GPP) in regions of three fire severity levels during 18 years. L, M, and H represent the low, moderate, and high severity burned areas, respectively.  
moderate and high fire severity were 0.009 and 0.014, respectively. The GPP in these areas exceeded the criteria level (1.0) after 2015, and it, in areas with high severity levels, largely exceeded the GPP in the reference area.