The Water-holding Performance Study On Three Types Forest Litter With Different Thinning Intensity In Qin Ling Mountains

The south to North Water Diversion Project in our country is important and strategic to resolve the shortage of water resources problem in the north(including East, middle and West Routes). The southern slope of the Qinling mountain is a major water source area among those routes, most of which are covered by forests, thus, the hydrological function of the forests have big influence on the water quality in this area. Forest litter is an important part of forest ecosystem playing a role of soil retention and water conservation, so it is meaningful to study the water holding capacity of litter under trees, The forests in this area was heavily cut down in the 1960 s, the existing forest are mainly man-made forest and natural forest after resumption. After 50 years of growth, the forests growth become slowly, a reasonable intervals to cut down trees is needed to promote the growth of trees.This research aimed at main forest types in Qinling mountain area, forest types of Pinus armandii.,Pinus tabuliformis and Quercus aliena var.acuteserrata.are choosen as subject investigated. By determination of forest litter cumulants, maximum water holding rate, maximum holding capacity and water absorption rate of the three types forest mentioned above at different thinning intensities, using comparative analysis method to analyse litter water holding characteristics, water holding capacity of different types of forest litter and the effect of thinning intensities on it, finally, the conclusions were obtained as follows:(1). With increasing thinning intensity, forest types of Pinus armandii., Pinus tabuliformis and Quercus aliena var.acuteserrata.showed a decreasing trend. With 20% thinning intensity treatment, Pinus armandii. forest litter cumulants decreased from 27.680 t/hm2 to 17.826 t/hm2 gradually; Pinus tabuliformis forest litter cumulants reduced from 29.532 t/hm2 to 19.072 t/hm2 steadily; Quercus aliena var.acuteserrata changed from 33.325 t/hm2 to 21.904 t/hm2. Comparing the three forest types, Quercus aliena var.acuteserrata presented the maximum cumulants forest litter, followed by Pinus tabuliformis and Pinus armandii. successively. What’s more, semi-decomposed litter cumulants were more than non-decomposed at the different layers in the same litter.(2). In different thinning intensities of forest types, for Pinus armandii forest, the maximum water holding rate of non-decomposed layer of litters was 217.742%~235.385%, semi-decomposed layer was 249.586%~273.230%; for Pinus tabuliformis forest, the maximum water holding rate of non-decomposed layer of litters was 218.232%~237.163%, semi-decomposed layer was 259.224%~293.848%; for Quercus aliena var.acuteserrata forest, the maximum water holding rate of non-decomposed layer of litters was 218.232%~237.163%, semi-decomposed layer was 305.109%~340.498%. Between different layers of forest litter in various types of forest, the maximum water holding rate of semi-decomposed layer of litters was more than non-decomposed layer always. For the three forest types, the maximum water holding rate of semi-decomposed layer of litters Quercus aliena var.acuteserrata forest was greater than Pinus armandii.,Pinus tabuliformis forest under any thinning intensities conditions. And, the maximum water holding rate of semi-decomposed litter was more than non-decomposed at the different layers in the same litter.(3). Water holding capacity type of both non-decomposed and semi-decomposed layers of litters was increased as time prolonged in various forest litters. There was a logarithmic relationship between water absorption time and water holding capacity of non-decomposed and semi-decomposed layers in various forest litters, most of the correlation coefficient were more than 0.9 using regression models, showing good fitting result.(4) The average water absorption rate reached at biggest at 0-2h, became slowly after 2h and tended to be stable when the time was 10 h both in non-decomposed and semi-decomposed layers of litters of the three types of forests of Pinus armandii.,Pinus tabuliformis and Quercus aliena var.acuteserrata.There was a power function relationship between water absorption rate and absorption time, most of the correlation coefficient were more than 0.9 using regression models, showing good fitting result. And, the water absorption rate of semi-decomposed litter was more than non-decomposed at the different layers of litters in the three types of forest.(5). With increasing thinning intensity, the maximum water holding capacity of Pinus armandii and Quercus aliena var.acuteserrata forests showed a trend of decreasing gradually. The maximum water holding capacity of Pinus tabuliformis forests presented the biggest without thinning intensity treetment, and sequenced as 10%, 5%, 15%, 20% and 25% intensities successively with thinning intensity treatment. Among the three forest types, the biggest water capacity were Quercus aliena var.acuteserrata, Pinus tabuliformis and Pinus armandii forests in descending order.With the maximum water holding capacity to measure water holding capacity of forest litter, Quercus aliena var.acuteserrata forests was optimal. All the three forest types presented a good statement with litters without thinning indensity.