Background  Soil and water loss is one of the important factors that restrict the ecological construction and development in hilly area of middle southern of Shandong province. Based the benefit evaluation results of soil and water conservation, selecting suitable forest species and creating mixed forest are important measures for ecological environment management under different site conditions in this area. In order to better to carry out the ecological work of soil and water loss in hilly area of middle southern of Shandong province, the soil and water conservation benefits of the mixed forests in this area were comprehensively evaluated and the appropriate mixed forest model was selected.

Methods  Twelve types 10-year mixed forests in typical limestone and sand mountainous areas of middle southern of Shandong province were selected as the research object, and the benefits from the soil and water conservation as well as the improvement of forest stand were studied by field investigation and indoor analysis. The weights of comprehensive benefit evaluation indexes of soil and water conservation were calculated by entropy weight method, and each mixed forest mode was evaluated based on TOPSIS principle. The comprehensive benefits of soil and water conservation in different mixed forests were evaluated by combining 13 indicators of soil and water conservation benefits, and the suitable mixed forest mode for the study area was screened out.

Results  1) In the limestone mountainous areas, for the mixed types of arbor and shrub, the benefit of soil and water conservation of the mixed forest of Platycladus orientalis and Armeniaca sibirica was the best, the soil improvement benefit of the mixed forest of P. orientalis and Cotinus coggygria was the best. Meanwhile, for the theropencedrymion, the benefits of soil and water conservation and soil improvement of the mixed forest of P. orientalis and Robinia pseudoacacia were the best. In addition, for the comprehensive benefits of soil and water conservation based on TOPSIS method, the mixed forest of P. orientalis and C. coggygria was the best in the mixed forest of arbor and shrub, and the mixed forest of P. orientalis forest and R. pseudoacacia forest was the best in the theropencedrymion. 2) In the sand mountainous areas, for the theropencedrymion, the benefits of soil and water conservation and soil improvement of the mixed forest of Pinus thunbergii and R. pseudoacacia was the best. And for the mixed types of broadleaved and broadleaved, the benefits of soil and water conservation and soil improvement of the mixed forest of R. pseudoacacia and Quercus acutissima were the best. 3) Also, according to the results of comprehensive benefit evaluation of soil and water conservation, the mixed forest of P. thunbergii and R. pseudoacacia was the best in the theropencedrymion, and the mixed forest of R. pseudoacacia and Q. acutissima was the best in the mixed types of broadleaved and broadleaved.

Conclusions  The results may provide the theoretical basis for the hybrid tree species selection of the artificial afforestation in hilly area of middle southern of Shandong province. Besides, the evaluation results based on the entropy weight and TOPSIS method are in fine agreement with the results obtained in other studies, and the evaluation method is recommended in the evaluation of soil and water conservation benefits of mixed forests.