## 4 Discussion
However, it is important to note that even though the \(\Delta\)NPV reaches pre-blowdown levels, it does not necessarily indicate full recovery of vegetation but merely that the spectral properties of the vegetation resemble those of pre-disturbance. The gap contours and shape of blowdowns (Figure 9) are still visible after recovery, suggesting that the pioneer vegetation within the gap is still in the growing stage and has not yet fully reached the level of the surrounding mature forest. Thus, longer observation periods are needed to determine if the regenerated vegetation will eventually reach maturity. The previous literature on gap recovery in tropical forests also shows that small gaps fully close in less than two years and larger gaps may take longer and up to five years to close while some may still be visible [15]. This could be due to the larger area occupied by fallen tree bases in bigger gaps, which can hinder the growth and regeneration of seedlings [55]. Therefore, we suggest future studies to stratify analysis of blowdown recovery time by gap size to further quantify these effects. Comparing Figure 6A,B, PlanetScope NICFI is more appropriate for monitoring the post-blowdown vegetation recovery process because it produces more coherent curves than Landsat-8. In terms of forest regeneration models, blowdowns are one of the gap disturbances, while the land cover type does not change, and the forest will gradually regenerate [56; 57]. Furthermore, Figure 6A also shows that post-blowdown forest regeneration is a complex process. NPV fraction sometimes fluctuates upwards during the gradual decline following blowdown disturbance. This phenomenon could be attributed to delayed tree mortality following the disturbance, as noted by [PERSON] et al. [58]. Possible contributing factors to this phenomenon include further damage to native and emergent vegetation by additional strong winds during the revegetation period or increased mortality of old trees within the sample pixels due to the gap created by the blowdown, which exposes them to disturbance, changes in microclimate, or other unknown reasons. In conclusion, not all trees perish during blowdown disturbances, and determining the exact cause of tree mortality post-blowdown remains a complex and unresolved issue [28]. However, it is important to highlight here that the vegetation recovery tracking in this study only included the blowdowns in the early growth stages of pioneer species. It did not follow blowdowns for longer than two years. This is because the NICFI program is only open for monthly mosaics whose date is after September 2020, before which only 3-month or 6-month mosaics are open. To obtain consistent monthly images, only blowdown events occurring after September 2020 and no later than May 2022 have been selected for this study. The PlanetScope NICFI catalog can be used in further studies which encompass mosaics produced monthly up to this day and expected until August 2024. While we have only investigated spectral mixture fractions--the most traditional data used for blowdown damage estimates--the presented results can likely be generalized to other vegetation indices, as the spectral recovery with vegetation recovery is also reflected on other spectral bands and vegetation indices [53]. One of the main contributions of this study is the understanding of \(\Delta\)NPV variability over time with recovery after blowdown occurrences. The studies on the detection of post-blowdown forest regeneration are limited to several discrete time points (e.g., six months, two years) after the blowdowns, but now, we raise the point that if we want to make consistent tree mortality estimates due to wind disturbances, a time series of observations would be required to correct for time since disturbance. One of the next steps in this research subject is to model \(\Delta\)NPV over time for blowdowns that consider multiple influencing factors.