Distance-dependent effects of road traffic on soil water content and vegetation biomass in protected grassland ecosystems

Road construction is integral to modernization but is often restricted in China’s nature reserves due to potential long-term impacts on ecosystem hydrology and biodiversity. This study examines the effects of a single-lane rural road on soil hydrology, vegetation, and soil properties in the Huihe National Nature Reserve, Inner Mongolia. Sampling plots were established along four transects at distances of 2 m, 10 m, 20 m, 30 m, 40 m, and 50 m from the road edge. Soil and vegetation data were collected during August of 2020 and 2021, and random forest analysis, correlation analysis, and structural equation modeling (SEM) were employed to identify key drivers of soil hydrology. Soil water content (SW) peaked at 30 m (47.27 %), which was 113.01 % higher than at 2 m and 16.43 % higher than at 50 m. Similarly, soil field capacity (FC), capillary porosity (CP), and total porosity (TPo) increased with distance, while bulk density (BD) and soil salinity decreased correspondingly. SW was positively correlated with aboveground biomass (AGB), belowground biomass (BGB), FC, CP, and TPo, and negatively with BD and salinity. The SEM explained 75 % of the variance in SW, revealing direct negative effects of road traffic disturbance on SW (β = -0.49, p < 0.01), along with indirect effects mediated by BD (β = 0.24, p < 0.05) and biomass (β = 0.57, p < 0.001). The road edge effect extenedd up to 30 m, where vegetation recovery and improved soil structure enhanced soil moisture and reduced BD. These findings highlight the importance of addressing road impacts in conservation planning and habitat restoration in protected areas.