| Catastrophic earthquakes always trigger many geological disasters.The strong impact on the geological environment within a certain range makes the geological environment in earthquake mountain areas extremely fragile.A series of secondary disaster events frequently occur,causing a lot of problems.Among them,strong earthquakes have caused a lot of negative effects on vegetation coverage and its natural growth.The severe destruction of vegetation and the large number of loose sources generated by the earthquake have caused the rainfall threshold of debris flows in strong earthquake areas to drop sharply.The dynamic change of vegetation can be used as a sign to indicate the development trend of landslide activity,and indirectly indicate the duration of post-earthquake risk.The occurrence law of geological disasters and vegetation restoration after the earthquake are a continuous evolutionary process.Existing research mainly focuses on large areas and large scales.There is a lack of quantitative assessment and analysis of the evolutionary mechanism of geological disaster changes and vegetation evolution in different regions.The main control factors and dynamic mechanisms of vegetation restoration and evolution are not well understood.In the Wenchuan earthquake zone,affected by multiple factors such as earthquake intensity,lithology,structure,climate,etc.,the effects of post-earthquake disasters in different regions are different.In order to increase the universality of the disaster evolution law after the Wenchuan earthquake,it is particularly important to conduct detailed research on different regions of Wenchuan,which is also a weak link in the current research.Therefore,dividing the Wenchuan earthquake into regions,studying the vegetation restoration process from a small-scale perspective,quantitatively assessing the impact of vegetation restoration on the slope stability in strong earthquake areas,and clarifying the vegetation restoration status and succession direction in different regional environments to provide a scientific and effective reference basis for further research on ecological restoration in strong earthquake areas.Regarding the issue above,three typical regions of Wenchuan County,Beichuan County,and Mianzhu Qingping Township,which belong to different climatic regions with different rainfall conditions and geological environments,are used as research areas in this paper.Using such high-time resolution images with the advantages of time consistency and long periodicity,the vegetation monitoring and post-earthquake landslide research are unified;then,the characteristics of the spatio-temporal evolution of the collapsed body,the vegetation restoration law in the strong earthquake area,and the differences in vegetation restoration in the three areas are studied.The main research results are as follows:(1)The long-term activity and hysteresis effect of the earthquake landslides in the three regions of Wenchuan,Beichuan and Mianzhu Qingping are very obvious,and the active areas of collapsed body in different regions show different attenuation rates.The distribution of slope,aspect and elevation of co-seismic collapsed bodies in the three areas is quite different.The elevation superiority distribution intervals of the collapsed bodies in Wenchuan,Beichuan,and Qingping are: 2000-2400 m,800-1050 m,and 1600-1900 m respectively;the slope superiority distribution intervals are: 40 °-50 °,30 °-40 °,40 °-50 °;the aspect advantage zones are: S,SE,E.The activity of the collapsed body after the earthquake showed a positive correlation with the slope and elevation as a whole,indicating that the activity of the collapsed body after the earthquake was more likely to occur in high and steep areas.(2)The seismic effect caused a significant increase in the activity of collapsed bodies after the earthquake.After the earthquake,the area of collapsed bodies in Wenchuan,Beichuan,and Qingping accounted for 33.60%,26.20%,and 26.91% of the study area respectively.As of 2018,the proportion of the active areas in Wenchuan,Beichuan,and Qingping to the area of the original collapsed bodies was 12.95%,12.75%,and 16.11%.With the passage of time,the area of the collapsed bodies showed a trend of power decay first and then slowly.(3)The average vegetation recovery rates of Wenchuan,Beichuan,and Qingping after the earthquake were: 0.026 / year,0.036 / year,and 0.038 / year,respectively and different regions showed different recovery rates.The highest proportion of vegetation restoration types in the Beichuan is Type III and IV,complete restoration,indicating that the regional vegetation succession process is different.The vegetation succession speed in this area is faster than that in Wenchuan and Qingping area,and the vegetation restoration is closer to the level before the earthquake.(4)The annual average decay rate of Wenchuan collapsed bodies is 7.85%,8.80% in Beichuan and 8.62% in Qingping,and the annual average decay rate of collapsed bodies is Beichuan> Qingping> Wenchuan;the NDVI reached good conditions and the landslide activity was basically stable in 2015 years,2013 years and 2012 years after the earthquake in Wenchuan,Beichuan and Qingping;the duration of the post-earthquake effect: Wenchuan> Beichuan> Qingping.(5)Affected by topography,geological disasters and climatic conditions in different regions,there are differences in vegetation restoration in the three typical study areas.Topography is an important factor that affects vegetation restoration.Elevation and slope affect the vegetation recovery rate and the vertical structure of the population.The density distribution of geological disasters affects the growth and distribution of vegetation,but it has a small effect on the succession degree of vegetation.The rainfall conditions affected the vertical structure of the vegetation restoration community in the earthquake-stricken area.In the areas with good rainfall conditions,vegetation restoration showed a faster benign progress succession trend.The degree of vegetation restoration in three areas: Beichuan> Qingping> Wenchuan. |
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