Abstract:Soil polarization refers to the shift of soil properties away from equilibrium toward unbalanced or extreme conditions due to the presence of a single tree species in pure stands of planted forests. In this study, we measured a broad range of soil properties in mature stands of pure and mixed forests at multiple sites in the semi-humid loess hilly region of northern Shaanxi Province, China. The results indicated that soil polarization reached the level of moderate or higher（P＞0.10）in almost all pure forests that were examined in this study and in which very strong polarization（P＞0.20）was observed for the following soil properties: chemical properties, biological properties and trace element content of Larix principis-rupprechtii and Betula platyphylla forests; chemical and biological properties of Platycladus orientalis forest; chemical properties and trace elements of Pinus armandii and Quercus liaotungensis forests; biological properties and trace element content of Robinia pseudoacacia forest; physical and chemical properties of Populus simonii forest. The results also indicated the following trends in soil polarization. Pinus tabulaeformis forest depleted the soil nutrient and trace element content. L. principis-rupprechti forest increased the soil trace element content but decreased the soil nutrient content. P. orientalis forest increased soil C and N content and improved soil biological properties. P. armandi forest improved soil physical properties, but depleted soil nutrient levels and caused a deterioration in soil biological properties. R. pseudoacacia forest increased soil nutrient content and improved soil biological properties, but decreased soil trace element content and caused a deterioration in soil physical properties. P. simonii forest decreased soil nutrient and trace element content and caused a deterioration in soil biological and physical properties. B. platyphylla forest improved soil physical properties and increased soil trace element content, but depleted soil nutrient content. Q. liaotungensis forest increased the soil trace element content. When we compared the level of soil polarization to the anti-polarization capacity of trees, we found more than moderate levels of polarization (I >0.40) for the following soil properties: soil physical properties of P. simonii forest ; soil physical properties, chemical properties, and trace element content of P. orientalis forest; all soil properties of L. principis-rupprechtii, R. pseudoacacia and B. platyphylla forest.