Objective To study quantitatively the multifactor relationships between the stand structure and soil and water conservation function of Pinus tabulaeformis plantation in the Loess Plateau of western Shanxi, so as to provide references for vegetation restoration in the Loess Plateau.

Method Sixteen standard sample plots of 20 m×20 m, which were further divided into sixty-four 10 m×10 m quadrats, were established for a tree census in Caijiachuan watershed of the Loess Plateau, Shanxi Province, China. The age of these trees was about 18 years. 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.

Result The results indicated that the horizontal structure of the P. tabulaeformis stand was the most obvious latent variable, which was expressed in the path coefficients corresponding to soil and water conservation (pc=−0.93) and sediment reduction (pc=0.79), respectively; the stand density and tree competition index were the major drivers of the structure, with path coefficients of 0.98 and 0.97 and influence coefficients of −0.987 and −0.956. These factors were easily regulated. The sensitive functional factors that were greatly affected by structural factors were the runoff yield, sediment yield and canopy interception rate. The path coefficients were 0.97, 0.91 and 0.69, respectively and the total impact coefficients were 0.986, 0.961 and 0.731, respectively. Otherwise, the topographic factor affected soil and water conservation function through affecting the stand structure. should be kept stable within the range from 1 100 to 1 400 trees/hm². Adjusting the stand density or tree competition index can effectively provide good benefits for soil and water conservation and sediment reduction. Multi-factor synergy can improve the vegetation quality and further promote the soil and water conservation efficiency in the ecologically significant loess area.