Objective This study aims to investigate the effects of water conservation forest types on the surface soil physicochemical properties and bioactivity indicators during the ecological restoration process in the mountainous area of southern Ningxia.

Methods Field investigation and laboratory analysis were conducted to investigate the effects of water conservation forests—7 a Larix gmelinii var. principis-rupprechtii, 15 a Larix gmelinii var. principis-rupprechtii, 7 a Pinus tabuliformis, 15 a Pinus tabuliformis, 7 a Robinia pseudoacacia, 15 a Robinia pseudoacacia, and 7 a Hippophae rhamnoides—on the physicochemical properties and bioactivity indicators of 0−20 cm surface soil in the Luotuolin watershed of the Liupanshan Mountains.

Results The results showed that compared to wasteland, L. gmelinii var. principis-rupprechtii and P. tabuliformis significantly increased soil porosity by 35.9% and 15.8%, respectively. As restoration periods increased from 7 a to 15 a, L. gmelinii var. principis-rupprechtii and P. tabuliformis significantly reduced the soil mean weight diameter (MWD) by 77.9% and 49.4%, respectively. Large soil aggregates with particle size > 5 mm in coniferous forests gradually transformed into small aggregates with particle size < 0.25 mm. Compared to wasteland, H. rhamnoides and R. pseudoacacia significantly increased soil organic matter content, and H. rhamnoides showed a more pronounced effect on enhancing soil nitrogen and phosphorus contents. Soil urease, alkaline phosphatase, and catalase activities increased gradually as restoration periods increased from 7 a to 15 a. Lower soil moisture and aeration under R. pseudoacacia were negatively correlated with the four soil enzyme activities and reduced the microbial activity in the surface soil.

Conclusions In summary, P. tabuliformis has the best performance in increasing soil fertility and water-fertility retention, making it a suitable choice as a dominant water conservation forest in the local area, thereby optimizing the local soil ecological environment.