Evaluation of vegetation and soil characteristics during slope vegetation recovery procedure

In recent years, the implementation of the development and construction projects has destroyed original ecological barrier, which results in a series of environmental problems, such as water losses and soil erosion, landslide, vegetation coverage degradation and diversity of species decrease, which will endanger human life and property safety. It is urgent and necessary to figure out the relationship between soil properties and vegetation growth, based on which measures can be designed and conducted to maintain stability and sustainable development of natural environment, as well as to recover or reconstruct the sites impaired by construction projects, and then keep life and property from threat damaged. In this study, 20 typical slope protection districts in Soil and Water Conservation Science and Technology Demonstration Park in Shangxinzhuang, Yanqing county of Beijing were chosen as evaluation units. Several parameters related to vegetation recovery were simplified into four independent principal components with specific functions using principal components analysis (PCA) method, including vegetation characteristics, soil physical properties, soil chemical properties and site conditions. Principal component scores were used for cluster analysis, and the 20 districts were divided into 3 groups. The comprehensive scores of every protection district were identified by using scores of 4 principal components and the corresponding eigenvalue weights, and then they were combined with the results of cluster analysis to assess the vegetation recovery effect of 3 types of slope protection districts. Margalef richness index, Pielou evenness index, Simpson index and Shannon-Wiener diversity index were used to evaluate inter-annual differentiation characteristics of vegetation community in different groups of districts and to construct 5 prediction models with different vegetation-soil degrees of coupling, within which the effects from both soils and plants were integrated. The results showed that: 1) Group I and Group II of districts, which mainly consisted of soil slopes, had significantly better vegetation restoration effect compared to Group III, which mainly consisted of rock slopes. 2) With the passage of time, the diversity index increased, the coefficient of variation decreased, and vegetation succession processed in a more dramatic manner in all groups of districts. 3) After 5 years of recovery, the vegetation-soil coupling coordination degrees of all districts achieved not so good coordinated development stage. Group I and Group II belonged to intermediate coordinated development stage, while Group III belonged to primary coordinated development stage. The vegetation-soil systems of all 3 groups of districts were in a transition period from primary coordinated development towards to intermediate coordinated development. The method of simplifying vegetation recovery factors by CPA combined clustering analysis to divide protection slope type is effective and it can not only ensure the data comprehensive, but also confirm the typicality when evaluating the vegetation recovery effect. In addition, the model constructed by soil properties and vegetation properties combined soil and vegetation system suitably which can evaluate the vegetation recovery effect in all protection districts. This research can guide the vegetation recovery of slopes damaged by construction projects for governors and executors. Measures of vegetation restoration in bare slopes and inner relationship of vegetation-soil need further investigation in the future.