## 4 Discussion
### Recovery Period and Legacy Effects  
The study estimates that the recovery period is 2 years, but the actual recovery period should be shorter than 2 years (24 months) and longer than 15 months. The recovery period was determined according to the legacy effect duration of the TC on the GPP of mangroves in Danzhou Bay, which was estimated by the values from October to December. What we can definitely infer is that the mangroves had not recovered to pre-disaster state by October-December 2017, but by October-December 2018, the mangroves had recovered to pre-disaster levels. It is undeniable that this study cannot fully determine whether the mangroves have recovered to the pre-disaster level between January 2018 and September 2018. This recovery period is also in line with the recommended survey time of using RS to assess the damage of the typhoon to mangroves within 18 months, the point where fallen leaves and broken branches but also actually surviving trees have basically recovered [73]. However, the recovery of surviving trees does not represent the recovery of ecosystem GPP. [PERSON] et al. [74] and [PERSON] et al. [24] investigated the recovery of mangrove forests directly attacked by typhoons in Category 5 on the Saffir-Simpson Scale (significantly stronger than the case in this study); [PERSON] et al. [74] found that, over a period of three years, the mangrove ecosystem could recover fully, and [PERSON] et al. [24] used the relationship ofrecovery time to estimate that the recovery time of different grades of damage ranged from 24 to 30 months. Small damage and short recovery time are reasonable and can be naturally recovered from in less than five years [75]. We found near linear recovery rates of mangroves for the total damage over time which is consistent with the report of [PERSON] et al. [24] that very high R-squared values near 1.0 indicate mangrove damage recovered near linearly for all damage levels but were different from the fast-then-slow pattern of mangrove recovery found in Florida. CW and LAI showed a nearly linear recovery, while CAB showed a trend of a fast-then-slow pattern, which is opposite to fCover change, finally resulting in a nearly linear trend of GPP recovery. Through the recovery patterns of CAB and fCover, it can be inferred that the mangrove ecosystem preferentially obtains a highly efficient unit photosynthesis rate followed by an increase in photosynthetic area. Due the fact that TCs mainly attack the tropics, the higher cloud cover year-round, and the fewer available images than for the middle and high latitudes [76], the single image taken in one month will have accidental values caused by such factors as the meteorological condition, so in this study, only months with at least three available images were selected in the analysis. Combining satellite imagery, near-Earth UAV aerial photography, and field surveys are recommended to increase the confidence and availability of data. SuperTy Sarika hit Danzhou Bay in October 2016, but due to the limitation that from 2015 to 2020 (the status before and after Sarika hit), not every October had available imagery, we utilized the image composed by the median of all available images from October to December of each year. A t-test was performed on the multi-year monthly images series, and it was possible to determine that there was no significant difference between the three months of October, November, and December. It can be clearly found that both fCover and LAI decreased significantly in 2016, confirming that typhoons can decrease GPP by reducing aboveground biomass, which determine photosynthesis area [77]. The reduction in GPP of the mangrove ecosystem caused by the TC is jointly exerted from the two aspects of ecosystem structure (LAI, fCover) affecting photosynthesis area and material content (CW and CAB) affecting photosynthesis rate. With the gradual recovery of these two aspects during the recovery period, GPP also returned to the pre-disaster state.