## 4 Discussion  
Forest biomass recovery began immediately after the forest fire in 2000, and gradually continued through to 2017. Although the July-August period is the most active forest growing season in South Korea, the vegetative activity in July-August 2000 is remarkable because it was so close to the time the forest fire occurred (May 2000). Indeed, in July-August 2000, vegetation increased in all damaged areas. In addition, the rate of recovery of areas with high fire severity was greater than that of areas with low fire severity. According to KFS reports and ground-survey data in the existing literature about the East Coast fire, the natural appearance of vegetation was observed in damaged areas in the first year after the forest fire [1; 49]. About 80% of the recovery was caused by the re-growth of surviving sprouts [49]. Also, [PERSON] and [PERSON] [50] showed that there was a rapid recovery for three years after the forest fire. However, the re-growth of surviving sprouts cannot fully explain the faster re-vegetation in areas with high fire severity. [PERSON] and [PERSON] [51] concluded that when larger disturbances such as forest fires occur, abundance in certain foliage is observed during the recovery period because of the enhanced re-growth made possible by less competition. The dominant tree type changed from pine to hardwood, such as oak species, after the forest fire [1]. Indeed, pine-hardwood and hardwood trees regenerated relatively rapidly compared to pine trees. The KFS conducted recovery efforts, such as tree planting, until 2005 [42]. For example, about 2-ha pine stand was planted in June 2003 [52]. The NBR\({}_{2.1}\), NBR\({}_{1.6}\), NDVI, and GPP data obtained during this study represented the integration of these phenomena. The relative ratio of variables in moderate (high) burned areas increased from about 8.0% (7.3%) to about 11.6% (14.1%) during the first 3-4 months after the fire in 2000. Also, the forest recovery trends  
Figure 6: Relative change in vegetation indices and GPP in the burned area compared with the reference area. Green lines indicate average value and green shadings indicate confidence intervals in the unburned forest area. Lines and error bar for blue triangles, yellow squares, and red stars indicate average values and confidence intervals in the low, moderate, and high severity burned areas, respectively: (**a**) NBR\({}_{2.1}\); (**b**) NBR\({}_{1.6}\); (**c**) NDVI; and (**d**) GPP. for 5 years after the forest fire showed quick changes in four variables (Figure 6). These results mean that the remote sensing based variables effectively indicate the progress of forest recovery. The NBR can indicate conditions of water and vegetation, and the NDVI can detect the amount of vegetation biomass. GPP is a measure of the rate of photosynthetic activity in vegetation chlorophyll. Therefore, these variables are governed by meteorological conditions. The seasonal variations of vegetation activity and water conditions in a forest are greatly influenced by the annual meteorological variation; this would affect the temporal patterns of forest recovery indicated by NBR, NDVI, and GPP. For example, in the spring drought in 2001, both the NBR\({}_{2.1}\) and NBR\({}_{1.6}\) in summer (July-August) 2001 were lower because the water deficit from the spring drought continued into the summer (Figure 5). Oppositely, the NDVI and GPP in summer 2001 were higher, possibly because of the higher photosynthetic activity caused by the reduction of clouds during the drought period [53]. To minimize the annual variation of the meteorological effects, a comparison between the burned and reference areas was carried out (Figure 6). All values of the indicators of forest recovery (i.e., NBR\({}_{2.1}\), NBR\({}_{1.6}\), NDVI, and GPP), which represented the conditions of the burned area, gradually became closer to the values of the reference forest. However, the time that it took for the values of the burned area to match the reference area values was different.