Effects of typical tree species and abiotic factors on hydrologic characters of forest litter in Beijing

Abstract: Litter layer affects hydrologic cycle of forest ecosystem significantly. This study aimed to determine hydrology characters of litter under different tree species and stand densities, and site conditions, and obtain the water holding capacity of litter forests, and the interception process and influencing factors through soaking experiment and rainfall simulating experiment. In order to estimate virtual interception, the relationships between virtual interception and the maximum water holding capacity were analyzed. Fifteen forest stands with different tree species, stand densities and site situations were chosen, and the fieldwork area was situated in Badaling national forest park，which was located in Beijing's rocky and earthy area of northern China. A rainfall circumstance was generated by an intermittent artificial rainfall simulator. In the rainfall simulating experiment, the parameters of rainfall intensity and rainfall amount were set as 5mm/h and 55mm for the simulator, because the rainfall intensity of 59 percentage of all rainfall events (2001-2012) was light rainfall magnitude (less than 10mm for a rain event), and 93 percentage of all rainfall events was less than 60mm in the study area. By outdoor survey, we found that the litter amounts of Pinus tabuliformis Carrière with different stand densities were not different significantly, except for the forest stands with the highest or lowest forest density. A positive correlation between litter amount and forest density was found in Pinus tabuliformis Carrière stands, no matter on ubac or adret. Litter amount differed with tree species, being less in broad-leaved forest than in coniferous forest, which was mainly caused by the lower decomposition rate of coniferous forest litter. The relationship between the maximum water holding capacity of litter and forest density could be described by a quadratic polynomials equation, the maximum water holding capacity of litter on adret was significantly higher than that on ubac (P<0.05). The maximum water holding capacity of the 5 typical forest stands ranged from 9.72 to 48.92 mm. The result of partial correlation analysis showed that most of influencing factors were positively related to the maximum water holding capacity, except for aspect, and the partial correlation coefficient of stand density was the highest, followed by tree species, decomposing layer percentage, slope, aspect, and litter amount, which indicated that the dominated factors of the maximum water holding capacity were complex and the factors affected each other. Rainfall simulating experiment result showed that the ratios of the interception to the maximum water holding capacity of different tree species increased with the increasing of rainfall, while rainfall reached 35-45 mm, the ratios became constant and ranged from 40% to 91%,which could be used to estimate virtual interception of litter, and this conclusion was different with Lee Richard's (1980). Two possible reasons might contribute to explain the phenomenon, At first, structure and material component of leaf litter of Platycladus orientalis (L.) Franco were quite different from other tree species, such as Pinus tabuliformis Carrière, and these differences made it need more time for the water content of litter to reach their virtual interception. Secondly, the rainfall intensity in this rainfall simulation was 5 mm/h, which was deemed as a typical light rain magnitude in northern China, and therefore the ratios of virtual interception to the maximum water holding capacity of the litter of mixed Platycladus orientalis (L.) Franco and Cotinus coggygria Scop. and Platycladus orientalis (L.) Franco could increase in other areas with the mean rainfall intensity bigger than 5mm/h. The conclusions based on the test data in this paper can provide reasonable information and suggestion for eco-hydrological study.