Objective The Bashang area, a crucial ecological barrier and water-conserving region in the Beijing-Tianjin-Hebei region of northern China, is the focus of this study. Our aim is to explore the influence of stand structure of typical protective forests on water conservation function of litter layer and soil layer.

Method Three types of typical protective forests (Pinus sylvestris var. mongolica forest, Larix principis-rupprechtii forest, Pinus sylvestris var. mongolica and Larix principis-rupprechtii mixed forest) in the Yudaokou Forest Farm of the Bashang area were selected as research objects. Stand structure parameters such as DBH, tree height, stand age, stand density, canopy closure, and leaf area index (LAI) were investigated. The water-holding capacity of both litter layer and soil layer was assessed using the indoor immersion method and the ring-knife technique. Redundancy analysis was employed to explore the influence mechanism of protective forest structure on the water-holding properties of litter layer and soil layer.

Result (1) The thickness of litter layer, volume of litter, maximum water holding capacity of litter and effective storage capacity of the mixed forest were greater than those of pure forest, and the difference of thickness was significant (P < 0.05). (2) The total soil porosity, water content and maximum water holding capacity of soil decreased as the soil layer deepened. The total soil porosity and maximum water holding capacity in the 0−30 cm soil layer showed Larix principis-rupprechtii forest > Pinus sylvestris var. mongolica and Larix principis-rupprechtii mixed forest > Pinus sylvestris var. mongolica forest, and in the 30−60 cm soil layer, it was showed as Larix principis-rupprechtii forest > Pinus sylvestris var. mongolica forest > Pinus sylvestris var. mongolica and Larix principis-rupprechtii mixed forest. (3) Redundancy analysis demonstrated that stand structure was closely related to the function of water conservation. Stand density and tree height had a significant influence on water conservation capacity of litter layer in different protection forests. Additionally, tree height and stand age had a significant impact on the water conservation capacity of soil layer in different protection forests (P < 0.05).

Conclusion Among the three types of typical protective forest, the Pinus sylvestris var. mongolica and Larix principis-rupprechtii mixed forest and Larix principis-rupprechtii forest have the best water-conserving capacity in litter layer and soil layer, respectively. Stand density, tree height, and stand age have a significant effect on their hydrological effects. Therefore, when conducting afforestation in the Bashang area, appropriate tree species, reasonable density, and scientific thinning methods should be selected according to the actual situation to improve the efficiency of moisture utilization. This study provides an important scientific basis for the tending management and stand optimization of typical protective forest in the Bashang area and has positive significance for maintaining ecological balance and sustainable development in this area.