## 4 Discussion  
Vegetation damage rate (VDR) is used for describing earthquake-induced vegetation damage. It is assumed that curvature of VDR could reflect abrupt decreases in vegetation related to earthquakes. Based on this assumption, a new method is proposed to quantitatively extract vegetation damage areas. To validate this method, information from 4751 points was collected by field survey, and 2950 of the points (62.09%) were located within the damaged area. The locations of other points outside the damaged area may be due to the following reasons. (1) The landslides were so small (areas less than 250 m \(\times\) 250 m) that MODIS could not recognize them; (2) The study area was located in mountainous regions covered with dense vegetation and some damaged regions may have been blocked due to the observation angle of the satellite; (3) The study area was covered by clouds that influence the extraction of landslides. Although the most effective monitoring of vegetation damage could have been achieved by using high resolution images such as Landsat TM or Quickbird, low levels of spatial coverage and high costs were the primary limitation. In this mountainous area, another consideration was cloud cover. Because of higher temporal resolution, it is easier for MODIS to remove cloud. Similarly to [PERSON] [18] and [PERSON] [15], vegetation recovery rate (VRR) was used and was divided into four classes for vegetation recovery assessment. However, there were some differences as follows: (1) More aspects were synthesized during the study (_i.e._, altitude, fault zones, earthquake intensity, soil texture and vegetation types); (2) Vegetation recovery was analysed over a longer time scale. Vegetation recovery was evaluated for the Wenchuan disaster area from 2009 to 2013, which corresponded to a five-year reconstruction period designated by the Chinese government. This information could provide a more realistic reference for the Chinese government department; (3) The transition matrix for vegetation recovery was applied. During the five-year study period, decreases in vegetation not recovering and recovering slightly promoted the increase of vegetation that largely recovered and vegetation that recovered fully. The most prominent transition was from the vegetation not recovering and vegetation recovering slightly to the vegetation that recovered largely. More interestingly, we also observed that 17.10% of the damaged area suffered degradation. These areas are primarily distributed on ridges or along rivers. This degradation may be caused by two reasons. One reason is that there is an insufficient water supply and poor topsoil on ridges. Another reason is that the Longmenshan Mountains have entered a new period of active geohazards following the Wenchuan [25]. Geohazards initiated by rainstorm will cause massive landslides and may block rivers and produce barrier lakes in five to 10 years [25]--an increase in erosion will occur between river banks and toe slopes. Vegetation recovery observed in our study was primarily distributed in the northeast and southwest regions of the study area. In the northeast regions, such as Qingchuan and Pingwu, vegetation recovered more easily because the relief is much lower than other regions and soil is fertile. However, it is noteworthy that in the southwest regions, such as Lixian, the vegetation recovery rate was also high, even though it is a mountainous region. Another similar finding is that vegetation recovery was stronger with increasing altitude (Figure 9). This may have been caused by two reasons. One reason is that the vegetation of the high altitude areas was damaged more severely, which provides potential for better recovery [16]. Another reason is that the vegetation was primarily located on the hillsides where sufficient water could be supplied for herbs. In addition, the proportion of vegetation not recovering at high elevations was also high. This vegetation was located along the ridges where there was a lack ofwater.