Efficacies of vegetation litter and roots in strengthening rainfall infiltration for different stand ages on the Loess Plateau

•The contribution of litter to infiltration was 1.56 times greater than that of roots.•The contribution of litter generally had an increasing trend with stand age.•Litter played a key role in strengthening uniform infiltration.•Roots played a key role in strengthening preferential infiltration. Vegetation litter cover and root systems have important effects on hillslope hydrological processes. Their relative importance may change with the stage of growth after afforestation. However, limited information is available on the dynamics of the quantitative contributions of litter and roots to rainfall infiltration. In this study, Robinia pseudoacacia plantations differing in stand age (18, 25, 30, and 40 years) and fallow slope land (control) were selected to investigate the influence of litter cover and roots on infiltration processes on hillslopes following simulated rainfall. Both the accumulation and decomposition rates of litter and the biomass of roots increased with stand age. Under the same simulated rainfall, infiltration in the plantations initially increased and thereafter decreased with stand growth, which was 2.93–4.91 times that of the fallow slope land. With increase in stand age from 18 to 40 years, litter contributed 60%, 11%, 82% and 91% to the increase in infiltration, and roots contributed 40%, 89%, 18% and 9%, respectively, to aforementioned four stands. The average contribution of litter to the increase in infiltration was 1.56 times greater than that of roots. The contribution of litter generally increased with stand age. Litter cover and the root system played a crucial role in strengthening uniform infiltration and preferential infiltration, respectively. In the presence of litter, the contribution of preferential flow to total infiltration was 67% of that in the absence of litter. These results contribute to an improved understanding of the effects of afforestation on hillslope hydrological processes and provide a theoretical reference for the management of plantations.