Positive effects of mixed-species plantations on soil water storage across the Chinese Loess Plateau

Soil water storage (SWS) is a key variable influencing hydrological processes and vegetation function in arid and semiarid regions. Although convincing evidence indicated that mixed forests have higher resistance and resil-ience to climate change and natural disturbance than monocultures, it is unclear how mixed-species plantations affect SWS. By conducting a meta-analysis of 1071 paired observations in mixed-species plantations and monoculture plantations from 45 studies, we showed that, on average, the SWS of mixed-species plantations at 0-500 cm was 10.81% higher than that of monoculture plantations. Importantly, these positive mixture effects increased over time, with greater positive effects in mixed tree and shrub plantations. The effects of mixed-species plantations on SWS shifted from positive to negative with increasing soil depth, and these mixing ef-fects in the topsoil layer (0-100 cm) became more pronounced with increasing stand age. However, the mixture effects on SWS did not vary with the mean annual temperature and precipitation. Moreover, mixed-species plantations were more conducive to enhancing the SWS capacity in areas with a low initial SWS. Structural equation models demonstrated that stand age was the main factor controlling the change in SWS, and soil depth also reduced the effect size of SWS by influencing the initial SWS. Our findings highlight that protecting and promoting functionally diverse forests improves SWS capacity, thereby alleviating soil moisture stress in arid and semiarid regions.