| The Loess Plateau is well known for its severe soil erosion. Soil erosion severely interferes with the process of plant development and succession. In this serious soil erosion region, plants can overcome stress and disturbance due to soil erosion through different survival strategies, and developed into plant communities that could resist soil erosion. This study was based on several years’ vegetation survey data of the Yan River basin in the hilly and gully region of the Loess Plateau. The definition of erosion-resistant species and Braun-Blanquet phytosociology methods were used to select potential erosion-resistant species. The community species composition of different recovery stages, plant growth and reproductive form characteristic, and plant niche breadth were used to explore its adaptation mechanism and its role in the plant community, and to analyze the evolvement rule of different erosion-resistant species. Plant community survey and analysis data under different soil erosion environments were used to elucidate the ability of different erosion-resistant plant communities to improve soil erosion environment in the vegetation recovery process. Plant community structure vegetation cover index and soil erosion data in different erosion-resistant plant communities were used to illuminate the community structure characteristics that could resist soil erosion. The main results are as follows:1) A total of 42 potential erosion-resistant species were selected, which belong to 18 families and 33 genera. Gramineae, Leguminosae, Compositae, Rosaceae occupied the dominant position in the study area; they were the main species in vegetation restoration succession process. Due to the climate in this region, the plant growth form was given priority to with shrub and herbs. Shrubs were mostly phanerophyte and chamaephytes, and herbs were dominant by hemicryptophytes. Plant water ecological type was given priority to with mesophyte and xerophytes.2) Forty-two potential erosion-resistant species maintained their own survival and reproduction through soil seed bank, plant crown seed bank, seed germination and dormancy strategies, seedling planting and vegetative propagation. They could adapt to environmental erosion by one or several mechanism of the special structure of anatomical morphology, thick protective tissue, developed palisade tissue, antioxidant mechanism and osmotic adjustment. The ecological niche breadth of different erosion-resistant species was from 0.023 to 0.359. The erosion-resistant species could be regarded as dominant species or accompanying species in the suitable habitat, it was an occasional species in other habitats.3) In the process of natural vegetation recovery, the erosion-resistant species began to habitat differentiation in herbaceous community late succession stages. Tree and shrub distributed in local region along gully slope, shoulder line of valley, etc of forest zone and forest steppe zone of Yan river basin, respectively. Shrub rarely appeared in steppe zone of Yan river basin. In the process of understory vegetation restoration under Robinia pseudoacacia plantation, the erosion-resistant species was less, only some annual weeds and Gramineous plants appeared under plantation. After Robinia pseudoacacia plantation decline, the mid and late stage species were the dominant species under plantation. During the period of relatively stable growth of the shrub plantation, there was no replacement of erosion-resistant species under plantation.4) The suitable community structure, which was formed by many species, was particularly important. The ground and underground complex hierarchical structure formed by different species could effectively improve soil environment. In addition, the improvement ability of erosion-resistant plant community was closely related to its habitat. In forest zone, phytocenosium structure formed by tree, shrub, herbs, and more litter were the main factors to improve soil environment. In forest steppe zone and steppe zone, plant fine root was the key factor to improve soil environment.5) Different communities have their own suitable structure vegetation cover index(Cs) that could effectively reduce soil erosion intensity. Early succession community and afforestation did not show a strong erosion-resistant, when the Cs were more than 20% and 30% respectively, and that the cover of herb layer and litter layer was higher, the soil erosion intensity was less than 2500 t km-2 yr-1. When Cs of mid and late succession communities, and natural tree and shrub communities were more than 30%, and 36% respectively, and that at least one of the cover of near surface layers(shrub, herb, litter layer) was higher, these communities could be effective in reducing soil erosion. Especially in the year of rainstorm, Gramineous plant communities and natural tree and shrub communities could effectively control soil erosion, when the Cs of these communities were more than 38% and 30-40%, respectively, and that at least one of the cover of near surface layers was higher, soil erosion intensity was smaller than soil loss tolerance in the Loess Plateau Region. The Cs value that community could effectively resist soil erosion had obvious difference in different hydrological years. In the year of rainstorm, the communities need to have higher Cs value when it was able to effectively reduce soil erosion. |
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