Objective  This paper aims to study the key evaluation indexes of soil anti-erodibility of Robinia pseudoacacia forest (16 years), and discuss the effects of stand density on soil anti-erodibility in the loess region of western Shanxi Province of northern China, which could provide functional guidance for the precise improvement of stand structure.

  Method  The research objects were five density gradients (1 025, 1 300, 1 575, 1 800, 2 150 tree/ha) of R. pseudoacacia forest. Based on field sampling and laboratory tests, 12 indexes about soil anti-erodibility had been analyzed.

  Result  (1) Principal component analysis showed that the soil bulk density, organic matter, > 0.25 mm water-stable aggregate, mean mass diameter, geometric mean diameter, fractal dimension and soil dispersion coefficient were key indexes to evaluate soil anti-erodibility of R. pseudoacacia forest, these factor loads were −0.776, 0.864, 0.747, 0.960, 0.779, −0.736 and −0.873, respectively. (2) Anti-erodibility of surface soil of R. pseudoacacia forest was stronger than that of deep soil under the same stand density, the comprehensive index of soil anti-erodibility: 0−10 cm (0.548) > 10−20 cm (−0.070) > 20−30 cm (−0.477). In the same soil layer, soil anti-erodibility increased with the increase of stand density (1 025−1 575 tree/ha) of R. pseudoacacia forest, and decreased when the stand density was higher than 1 575 tree/ha. (3) Taking the stand density of R. pseudoacacia forest as the x-axis and the comprehensive index of soil anti-erodibility as the y-axis, the parabolic function relationship with opening downward was established: y = −2.683 × 10⁻⁶x² + 0.009x − 6.375 (R² = 0.77), soil anti-erodibility was the strongest when the stand density of R. pseudoacacia was 1 590 tree/ha, and the comprehensive index was 0.403.

  Conclusion  Soil anti-erodibility of medium density R. pseudoacacia forest is strong. From the perspective of soil anti-erodibility, the management density of R. pseudoacacia forest (16 years) should be 1 590 tree/ha in the loess region of western Shanxi Province. For the stand with too low or too high density, scientific replanting or thinning should be carried out in time while meeting the forestry production. Attention should also be paid to the protection of topsoil, so as to give full play to the water and soil conservation function of forest land and effectively control soil erosion.