Spatial-Temporal Dynamic Monitoring of Vegetation Recovery After the Wenchuan Earthquake

Mountainous vegetation recovery after major earthquakes has important implications for preventing postseismic soil erosion and geo-hazards. However, regional recovery processes of the postseismic vegetation and its spatial patterns have not been thoroughly studied. In this paper, we examined the vegetation recovery processes following the 2008 Wenchuan earthquake (Ms. 7.8) using 16-day interval MODIS normalized difference vegetation index time series from 2000 to 2014. The Savitzky-Golay filter and cross-correlogram spectral matching were used to eliminate the influences of cloud and intraannual phenology. Change vector analysis was applied to measure the postseismic vegetation recovery conditions for each year. We find that the heavily affected vegetation areas are mainly located along the southern part of the earthquake surface rupture. Additionally, five major affected vegetation types have been identified: shrubland, grassland, broadleaf/mixed, needleleaf, and plantation. Shrubland represents the largest fraction of vegetation type in the heavily affected area, whereas plantation comprises the smallest fraction of vegetation type in the heavily affected area. Further analysis indicates that the changing trend of postseismic vegetation conditions in the first six years can be grouped into three classes: recovering, fluctuating, and deteriorating. Recovering and fluctuating classes cover 59% and 37% of the heavily affected areas, respectively, and are the two dominant postseismic vegetation classes. In contrast, the deteriorating recovery class covers just 4% of the affected areas. The recovering vegetation is primarily located around the epicenter, and most of the fluctuating classes is located to the northeast of the epicenter. These results demonstrate that the Wenchuan earthquake has long-term and important influences on mountain vegetation, and more attention should be given to the locations of deteriorating and fluctuating vegetation following mountain disasters.