Study On Hydrological Characteristics Of Litter And Soil In Tropical Rainforest In Jianfengling, Hainan Island

As important layers of the forest ecosystem, forest litter layer and forest soil layer provide many important and unique ecological functions, such as runoff regulation, soil and water conservation and water conservation. Jianfengling tropical forest is one of the typical tropical rainforest ecosystems in China, with frequently occurred rainstorm and typhoon. Therefore, its litter and soil layers are especially important to prevent soil erosion and conserve water. In this paper, based on the 161 grid quadrats and three permanent plots in Jianfengling, the hydrological characteristics of litter and soil were stuied by the field monitoring and simulated experiment, so as to provide reference for the research of water blance and the assessment of eco-hydrological benefit of tropical rainforest in Jianfengling or even other tropical region. The main results were as follows:(1)The hydrological characteristics of tropical rainforest litterThe results based on the 161 grid quadrats showed that the litter standing crop ranged from 3.23 t/hm~2 to 12.76 t/hm~2 and average value is 6.46 t/hm~2. The max water holding capacity ranged from 5.32 t/hm~2 to 19.23 t/hm~2 and average value is 10.40t/hm~2. The order of max water holding rate of litter was clear-cut forest(169.2%)>selectively logged forest (168.0%)>primary forest (155.6%). They are significantly different by the Kruskal-Wallis H test.The results based on three permanent plots (located in the mountain primary rainforest, mountain secondary rainforest and lowland primary rainforest, respectively) showed that the annual average litter standing crop were 5.89, 6.13 and 5.23 t/hm~2, respectively. However, there are not signficantly different among the monthly values although the"abnormal litterfall"increaseed abruptly in some months because of the influence of typhoon. The natural water holding rate and the modified interception amount of litter are significantly different between the rainy season and the dry season. The mean natural water holding rate of litter are 78.8%, 68.0% and 38.9% in the dry season, while they are 113.6%, 107.0% and 102.5% in the rainy season in three permanent plot respcetively. The modified interception amount of litter ranged from 2.86 t/hm~2 to 4.62 t/hm~2 in the dry season and ranged from 1.26 t/hm~2 to 2.81 t/hm~2 in the rainy season.The immersion testing for the litter showed that the water holding capacity and water holding rate increased logarithmically with increasing soaking time. While, water absorption rates decreased according to equation W= a t-b with increasing soaking time. Both of them have determination coefficients (R2) larger than 0.96.(2)The hydrological characteristics of tropical rainforest soilThe results based on the 161 grid quadrats showed that the soil bulk density ranged from 0.74 g/cm~3 to 1.67 g/cm~3, and the total porosity ranged from 33.6% to 61.6% of the 0-30 cm soil layer. The maximum water retaining capacity in 30 cm soil layer ranged from 100.2 mm to 184.8 mm, and the effective water retaining capacity ranged from 8.34 mm to 63.96 mm of the 0-30 cm soil layer.The results based on three permanent plots (located in the mountain primary rainforest, mountain secondary rainforest and lowland primary rainforest, respectively) showed that the weighted average soil bulk density ranged from 1.31 g/cm~3 to 1.55g/cm~3, and the total porosity ranged from 36.8% to 47.4% of the 0-100 cm soil layer. The maximum water retaining capacity of ranged from 365.9 mm to 473.9mm of the 0-100 cm soil layer in three permanent plots. The maximum water retaining capacity was closely related to the physical properties of soil in three forest types.The result based on the continuous field monitoring showed that, the monthly dynamic changes of soil moisture concent is bimodal in the mountain primary rainforest and the mountain secondary rainforest. While, it is unimodal in the lowland primary rainforest. The maximum and the minimum values of soil moisture concent value of soil moisture concent occured in October and March, respectively. There were also significantly different between the dry season and the rainy season for the soil moisture concent in all three forest types.The correlation analysis showed that in mountain primary rainforest and mountain secondary rainforest, in the rainy season, the soil moisture concent was significantly correlated to rainfall and air humidity positively. They were significantly correlated to air temperature and net radiation negatively. In the dry season, the soil moisture concent were significantly correlated to air humidity, air temperature, wind speed and water vapor pressure, but the concrete conditions were complicated.The multiple stepwise regression analysis showed that the soil moisture concent was influenced by the meteorological factors in the mountain primary rainforest and mountain secondary rainforest. The regression model between soil moisture concent and meteorological factors in the rainy season is better than that in the dry season.