Background The distribution of vegetation roots on slopes is complex phenomenon. Erosion processes, strong runoff, or sediment disturbances can cause roots to be exposed, and in some cases, may even uproot plants completely, compromising their ability to effectively stabilize the soil. The phenomenon of exposed roots due to soil erosion is prevalent, especially in the Karst areas with shallow soil layer. Although exposed roots play a significant role in calculating erosion rates, their exact impact on the erosion characteristics of karst sloping land remains unclear. This limitation hinders a comprehensive understanding of erosion processes and mechanisms in this area.

Methods The experiment selected the root systems of representative tree species in the research area, such as acacia and camphor trees, as the research objects. By using an excavation method to obtain coarse roots of 15-20 mm, different distribution patterns of exposed roots on the slope surfaces were established, such as parallel slope arrangement (PSA), transverse slope arrangement (TSA), cross slope arrangement (CSA), and bare slope. The artificial simulated scouring test method was utilized to measure the initial runoff production time, runoff characteristics, and sediment characteristics on the slope surface under varying test conditions. The one-way analysis of variance was used to compare the differences between the data.

Results The results showed that 1) under different experimental conditions, the initial flow production time of the slopes varied, with the highest initial runoff production time on the slope surface observed in the cross slope arrangement, followed by the transverse slope arrangement, parallel slope arrangement, and bare slope. In the cross slope arrangement, the initial runoff production time exceeded 5 mins, which was 3.78 times longer than that of the bare slope, 5.62 times longer than that of the parallel slope arrangement, and 6.33 times longer than that of the transverse slope arrangement. 2) The distribution arrangements of exposed roots showed variations in surface runoff under different experimental conditions, with surface runoff being the main contributor to erosion processes, accounting for more than 80%. Surface runoff was primarily displayed as bare slope > transverse slope arrangement > cross slope arrangement > parallel slope arrangement. Subsurface runoff, on the other hand, followed a different pattern: parallel slope arrangement, transverse slope arrangement, cross slope arrangement, and bare slope. In general, subsurface runoff tended to occur more frequently along parallel slope arrangement, cross slope arrangement, transverse slope arrangement, and bare slope. 3) In the dynamic process of sediment production on the slope under different experimental conditions, there was a trend of initial increase followed by a decrease, ultimately stabilizing. The total sediment production by parallel slope arrangement was 0.31 kg, which was 1.29 times than that of transverse slope arrangement, 1.38 times than that of cross slope arrangement, and 1.41 times than that of bare slope.

Conclusions The presence of exposed roots altered the initial slope production time, the runoff distribution is dominated by surface runoff, increasing the erosion process and varied depending on the distribution patterns of the exposed roots. These findings enhance our understanding of how plant roots impact slope erosion and serve as a scientific basis for designing and optimizing vegetation measures for soil and water conservation.