Effects of Zanthoxylum bungeanum planting on soil hydraulic properties and soil moisture in a karst area

Zanthoxylum bungeanum plantations in karst areas in China are important for economic reasons and for restoring the ecological environment. However, the lack of water resources in karst areas will affect the growth of Zanthoxylum bungeanum and the restoration of the ecological environment. Studying the influence of Zanthoxylum bungeanum on soil hydraulic properties and soil moisture in karst areas is important to optimize management of Zanthoxylum bungeanum planting and for ecosystem vegetation restoration. In this study, 4-year-old and 11-year-old Zanthoxylum bungeanum forest sampling sites were selected, and abandoned land was used as a control site; 0–50 cm undisturbed soil samples were collected to determine the soil hydraulic properties, as well as the basic physical and chemical properties. Soil volumetric water content sensors were installed at 10, 25, 40 and 55 cm depths in the soil profile at each sampling site to measure the soil moisture dynamics (from May 12, 2018, to October 3, 2018). The results showed that Zanthoxylum bungeanum had a significant impact on the shallow soil hydraulic properties, i.e., reduced soil bulk density, increased field moisture capacity, porosity and soil moisture, and enhanced soil water holding capacity; these changes increased with the time since planting. Additionally, the rainfall responses and rainfall replenishment of soil water at the three sites were significantly different. The dynamic change in soil moisture in the shallow layer was mainly affected by precipitation and atmospheric temperature (evaporation), which resulted in rapid changes under dry and wet conditions, while soil moisture in the deep layer was mainly affected by precipitation recharge, which resulted in a long retention time. With the increase in time since the planting of Zanthoxylum bungeanum, the hysteresis of the soil moisture response to rainfall strengthened, and the soil water storage and stability improved. This study shows that the planting of Zanthoxylum bungeanum improved the shallow soil hydraulic properties in karst areas and can play a positive role in water conservation.