## 5 Discussion
### Vegetation Recovery in the Earthquake Triggered Hazard Areas  
Opinions differ with regard to the potential for vegetation recovery in the hazard region. [PERSON] _et al._[24] thought that an ecological restoration of the areas affected by landslides would be quite difficult because of the severe damage to the local environment caused by the earthquake. In contrast, [PERSON] _et al._[51] researched the impact of the Wenchuan earthquake on biodiversity and found that despite bare rocks comprising the largest area of ground cover in the earthquake-damaged areas, a high percentage of the damaged areas contained remnant vegetation, suggesting that future vegetation recovery is likely. An experiment done by [PERSON] _et al._[52] in 1981 also found that forest ecosystems had strong self-healing capabilities after the external environment had changed, as happens with earthquakes and forest fires, and the seeds buried in the soil or under the surface would play an important role in the process of vegetation recovery. During the first year after the earthquake, the seeds sprout quickly from the soil, and the dominate species are herbaceous plants. Other previous studies suggested that the presence of remnant vegetation is a driving factor for forest recovery [53, 54]. Furthermore, [PERSON] _et al._[36] found that local vegetation productivity in heavily affected areas had recovered to 84% and 87% after one and two months, respectively.  
Our results demonstrate the possibility of vegetation recovery in earthquake-affected areas even under harsh conditions in some areas, and a positive correlation was found with geological hazard variation (Figure 11). In the one to two years after the earthquake, the loose soil produced by the earthquake combined with the sliding of the entire landslide mass in some hazard regions made it easier for the vegetation to recover. Community types of shrub and grass grew quickly in this period, resulting in the fastest vegetation recovery period. Subsequently, the vegetation recovery slowed due to woody plant re-establishment. The recovery patterns in the hazard areas were complex, with factors such as the terrain and soil also affecting the recovery's progress [3] and making vegetation recovery difficult (as with the No. 14 and No. 15 sites in Table 5).  
Similarly, the vegetation recovery was analyzed according to elevation and slope data (Figure 12). The vegetation recovery mainly occurred in elevations below 3,000 m, accounting for 99.27% and 99.15% of the total debris flow area in 2008 to 2009 and 2009 to 2011, respectively, and the peak occurred between the elevation of 1001-1500 m because of the abundant accumulated soil mass, which was suitable for vegetation growth, produced by the landslides and debris flows. The slope of the surface also have a obvious influence on the progress of vegetation recovery, and more than 60% of the vegetation recovery were concentrated on slopes between 31 \({}^{\circ}\) and 50 \({}^{\circ}\), the peak occurred  
Figure 10: Relationship between newly developed debris flow area and topographic factors.  
between the slope of 41-50 \({}^{\circ}\), [PERSON] _et al._[55] and [PERSON] _et al._[3] also observed similar results, they suggested that grass species that survived during this slope range facilitated the vegetation growth when adequate rainfall was supplied to the area. In addition, the good soil holding and storing water condition for the plants in the hazard sites is also critical to the vegetation recovery.