Dead-fallen shrubs improve soil quality and promote herb seedling settlement in an arid sandy land of northern China

Shrubs planted to combat desertification in China’s arid sandy lands often succumb to water deficits, yet the effects of dead-fallen shrubs on soil quality and herb establishment remain unclear. This study investigated soil properties and herb seedling settlement across bare sandy land (BSD), standing living shrubs (SLS), and dead-fallen shrubs at three decay stages (3–5, 7–9, and 11–12 years) in China’s Mu Us Sandy Land. Soil temperature, moisture, enzyme activities, physicochemical properties, and herb parameters (height, density, coverage, biomass) were analyzed and overall soil quality index (SQI) was calculated. Results revealed that dead-fallen shrubs significantly reduced soil temperature, increased soil water storage, improved soil physicochemical properties, eventually leading to a higher SQI under dead-fallen shrubs and a lower SQI under BSD and SLS in 0–5 cm soil. The herb seedling settlement parameters under dead-fallen shrubs were also higher than both under BSD and SLS. Regression analysis indicated that seedlings height, density, coverage and biomass were positively correlated with SQI, both in 0–5 cm and 5–10 cm soil. Structural equation modeling revealed that herb seedling settlement at 0–5 cm was driven by physicochemical properties, while at 5–10 cm soil depth relied on physical properties. Soil temperature exerted a direct negative influence on herb seedling establishment in both soil depths. This study highlighted that dead-fallen shrubs, particularly at advanced decay stages, outperform living shrubs in enhancing soil quality and facilitating herb establishment by modulating microhabitats and nutrient cycling, offering novel insights for sustainable restoration in arid ecosystems.