Hydrological responses to litter density on runoff-infiltration patterns and water conservation in Pinus tabuliformis plantation

Leaf litter alters the distribution of rainfall and thus affect evapotranspiration and soil water storage (SWS), especially in areas with deep soil layers. Few studies have characterized the hydrological responses to leaf litter density in afforested ecosystems. Ten runoff plots of five litter masses, 0, 0.6, 0.9, 1.2 and 1.8 kg/m2 (referred to as 0LM, 0.6LM, 0.9LM, 1.2LM and 1.8LM, respectively), were established in a Pinus tabuliformis plantation to investigate the compound effects of litter density and rainfall on runoff generation, throughfall infiltration and water conservation in the rainy season of 2020–2021. The runoff coefficient (ɑ) was 0–0.80 mm/mm during rainfall events. With the exception of litter density, runoff generation was further affected by wind speed and rainfall intensity, especially during small rainfall events. In general, the runoff yield (R) was 51.8%, 63.8% and 83.9% lower in 0.6LM, 1.2LM and 1.8LM, respectively, than in bare soil. Higher litter density and greater throughfall (P) promoted the infiltration of P to deeper soil layers, and the wetting depth of 1.8LM increased from the 0–20 cm soil layer during small rainfalls to the 0–50 cm soil layer during large rainfall events in 2021. Moreover, thick litter had greater capacity in throughfall interception (I), partially contributed to the negative values of SWS during small rainfall events and rainless periods. A total of 0–8.7% of P was consumed in I, and 26.4%, 33.1%, 38.5%, and 40.2% of P contributed to SWS in 0LM, 0.6LM, 1.2LM, and 1.8LM, respectively. With the exception of the R/P of 1.2LM, which was a little higher than that of 1.8LM, the water conservation capacity of 1.2LM was similar to that of 1.8LM. This study may enhance our understanding of the eco-hydrological function of litter and will aid the sustainable and ecological management of plantations in Chinese Loess Plateau.