Abstract
Ninety-six sample plots were established for a tree census to explore the multifactor relationships between the soil and water conservation functions and the stand structure in a typical black locust (Robinia pseudoacacia L.) plantation in the Caijiachuan watershed of the Loess Plateau, Western Shanxi Province, China. Based on the observational and experimental data, a topography-structure-function model was built using a structural equation modeling (SEM) approach. The latent variables were the topographical factors, horizontal structure, vertical structure, soil and water conservation, and sediment reduction. The results indicated that the horizontal structure of the Robinia pseudoacacia L. forest was the most obvious latent variable, which was expressed in the path coefficient (pc = 0.85) corresponding to the sediment reduction; the stand density and tree competition index were the major drivers of the structure, with path coefficients of −0.96 and −0.92 and influence coefficients of −0.997 and −0.998. These factors are easily regulated. Among these factors the stand density of the arbor layer is recommended to be kept stable within the range from 1600 to 1700 trees/hm2. These relationships showed that reducing the tree competition index and changing the microtopography could effectively enhance the soil and water conservation functions in this ecologically significant loess area.
Highlights
Soil and water conservation studies have been conducted on the Loess Plateau since 1950, and the ecological environment of this area has gradually recovered and improved as a result of afforestation and vegetation restoration [1,2]
The vegetation of the nested Caijiachuan watershed is characterized by artificial shelterbelts of black locust (Robinia pseudoacacia L.) with a forest cover rate of up to 72% that covers an area of 38 km2
The results showed that the slope, aspect, elevation, DBH, tree crown area, canopy density, stand density, uniform angle, neighborhood comparison, tree competition index, tree height, leaf area indices (LAIs), stand layer index, canopy interception rate, water retention rate of litter in the undecomposed layer, water retention rate of litter in the semidecomposed layer, soil infiltration rate, soil moisture content, maximum water holding capacity (WHC), soil organic matter (SOM), total phosphorus (TP), average runoff yield, and average sediment yield met the inclusion criteria, and these indicators were incorporated into the model
Summary
Soil and water conservation studies have been conducted on the Loess Plateau since 1950, and the ecological environment of this area has gradually recovered and improved as a result of afforestation and vegetation restoration [1,2]. During this process, the artificial forests grew slowly and showed premature senescence, and many even died due to excessive density in afforested areas. The expected levels of soil and water conservation and the ecological benefits of artificial afforestation are not currently being met.
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