The Study On Regulation Mechanism Of Precipitation Input Process In Chinese Fir Plantations

With the rapid development of economy and society, water shortage becomes a bottleneck of regional development gradually. To solve the water shortage problem, studying regulatory mechanism of forest system on the formation process of water resource is very important. Our study applied representative forest type in subtropical area of China, the Chinese fir plantations, as research object. To solve the theoretical and practical problems and observe the relationship between forest and water on lots of aspects, we combined the experimental observation in the small catchments with the29years data collected successive observation at Huitong National Field Station for Scientific Observation and Experiment. The coupling rules of eco-hydrological processes in Chinese fir plantations in growth phases were investigated, such as precipitation and water transmission in canopy layer, interception, litter water-holding, to provide a theoretical basis for the scientific management of Chinese fir plantation and construction.According to the annual rainfall recorded from1983to2011, the total rainfall at research area was37435.1mm, and the average rainfall was1290.9mm· a-1. The rainfall was the heaviest from April to August every year. There were1866times of rainfall in these months, which was45.08%of the total number.The research shows that the input and precipitation distribution of Chinese fir plantation were determined by the canopy. So the law of monthly input and precipitation distribution were similar at growth phases of Chinese fir plantation. The through fall at growth phases increased with the increasing rainfall. The interception capacity also developed with the increasing age of forest, and so did the annual average canopy interception rate. The annual average canopy interception rates at growth phases of Chinese fir plantation were:26%at Fast growing stage,27.86%at stemwood stage, and29.47%at Maturity stage. The Chinese fir plantation does not produce stemflow in fast growing stage, but when the tree steps into stemwood stage, it produced little stemflow due to the certain rainfall intensity, accounting for1%of the gross rainfall per year. With the increasing rainfall, the through water increased; in other words, the relationship between rainfall and through water was a linear relationship.The changes of interception and interception rate at growth phases were very similar, according to the law that when rainfall was little, the interception rate was high; when it rains heavily, the rate reduced sharply. In addition, the interception and interception rates would be in steady state under the certain rainfall intensity. In a word, the interception capacity of canopy of Chinese fir plantation increases with the increasing development of tree, and the capacity of different growth phases was:maturity stage> stemwood stage> fast growing stage. The interception capacity of Chinese fir plantation at fast growing stage would become stable when rainfall reaches17-34mm, which was less than that of stemwood stage (23-50mm) and maturity stage (25-47mm).According to the regression analysis on interception ratios at growth phases, we can conclude that the relations between rainfall and interception ratio were similar. Exponential function regression equations were as follows:Fast growing stage:PIR=64.118P-0.5187, R2=0.986; Stemwood stage:PIR=71.034P-0.4502, R2=0.980; Maturity stage:PIR=72.067P-0.4444, R2=0.976. These equations aptly reflect the relations between rainfall and interception ratio at growth phases, with more than0.97R square values.The undecomposed layer water-holding capacity of litter in Chinese fir plantation was going up with the increase of immersing time at different forest age. The relationship of the decomposed layer water-holding capacity of litter at different age shows that maturity stage> stemwood stage. And the litters half-had decomposed layer of water-holding capacity also increased with immersing time. The absorption rates of undecomposed layer and half-had decomposed layer of litters were the highest when the litters were immersed into water for0-1/2hour, which shows that litters could protect surface runoff efficiently. The litters in forests could retain water when rained heavily in a short time. Comparing various absorption rates of different litters, we can conclude that the speed of half-had decomposed layer was higher than that of undecomposed layer.