Study On Hydrological Effect Of Litter In Main Forest Types In Suburb Of Nanjing

This paper was based on 4 typical types of Nanjing forests, carrying out continuous observation and analysis on litter moisture content of Quercus acutissima, Cunninghamia lanceolata, phylostachys edulis and Pinus massoniana, to investigate the characteristics of litter hydrological effect of different forest types. The results showed that:(1)From indoor saturated water immersion test, we found that litter water absorption rate(mm/h) decreased with the increase of soaking time(H), corresponding with Power function(y=atb), and litter water holdup(%) increased with the increase of soaking time(H), in line with the S function equation y=ea+b/t(water holdup is y, soaking time is t); Viewing from the maximum water holding capacity of litter, Quercus acutissima > phylostachys edulis > Cunninghamia lanceolata > Pinus massoniana. Establishing a model of loss process of litter moisture content by the hour scale after the rainfall, we found that litter moisture content of these 4 types of forest declined rapidly, then after 3-5 days, with the increase of humidity and decrease of temperature, litter moisture content increased accordingly, reaching the dynamic balance period when decreased during the day, and elevated at night.(2)Under natural conditions, litter moisture content was not only affected by the forest type, but also related with the factors of outside meteorological factors and soil moisture content. Litter moisture content of Quercus acutissima(33.46%) was greater than phylostachys edulis(31.40%) and Pinus massoniana(29.17%),and litter of Cunninghamia lanceolata had the minimum moisture content(24.88%); but the amount of litter precipitation interception ordered as Quercus acutissima(6.04 t/hm2)> phylostachys edulis(4.14 t/hm2)> Cunninghamia lanceolata(2.44 t/hm2)> Pinus massoniana(1.13 t/hm2). Broad-leaved evergreen had the higest litter moisture content and litter of deciduous broad-leaved forest had the maximum amount of precipitation interception.(3)Litter moisture content of these 4 types of forests had significant or extremely significant correlation with relative humidity, soil moisture, solar radiation, wind speed, temperature and other environmental factors in different seasons, specifically, litter moisture content had negative correlation with solar radiation, wind speed and temperature, and in contract, it had positive correlation with precipitation, soil moisture content and relative humidity. Establishing multiple stepwise regression model between litter moisture content of these 4 types of forest and environmental factors, we found that determination coefficient was high and reached significant level. Besides, litter moisture content of broad-leaved forest fit the experimental data better than coniferous forest.(4)Precipitation can significantly increase the moisture content of litter, but operated with a lag. Change of litter moisture content was divided into rainfall-recharged period, subsided period of water loss and dynamic balance period. During rainfall-recharged period, litter moisture content increased along with rainfall duration which was in accordance with the linear growth model; during subsided period after rainfall, litter moisture content decreased slowly with time, in line with the exponential decay model; during dynamic balance period, litter moisture content fluctuated with the change of temperature, relative humidity and other meteorological factors. This paper constructed a seasonable moisture content model, and simulated litter moisture variation relatively accurately(r=0.9426).