Investigation On The Water Conservation Function Of Pinus Massoniana Plantation In Hubei Water Source Region Of Danjiangkou Reservoir

Water conservation ability,one of the most important functions of forest ecosystem,plays a key role in the functions of forest ecosystem.It is also the key for sustainable development in the coordination regions,cycle of the nutrients in the water,conservation of species diversity.However,due to the increased human activity,advancement of urbanization,and destruction of ecological environment,the situations of global water shortage and deterioration of water quality become worse and worse in recent decades.The investigations of forest hydrology thus have attracted attentions of researchers.South-North Water Diversion Project,a national strategic project with the largest cross-basin water transportation in the world,plays a significant role in alleviating the water crisis in the north,optimizing the allocation of water resources,and promoting comprehensive and coordinated sustainable development.Considering the serious soil erosion and water pollution,Danjiangkou Reservoir,as he midline source of the South-North Water Diversion Project,is key in maintaining a clean water environment,achieving sustainable usage of water resources,winning the battle of“protecting water,welcome water diversion”,and guaranteeing a continuous diversion of clean water to the north.Taking into account the importance of forest ecosystem in Danjiangkou Reservoir to the water resource and water environment safety in the region,we examined Pinus massoniana plantations in Longkou Forest Farm from June to September 2018 based on Danjiangkou City second-class survey data using both field observations and laboratory analysis with Hubei water source region at Danjiangkou Reservoir as the investigation area,.To evaluate the water conservation ability in the Hubei water source area and explore the effects of forest density on its water conservation ability,three densities（i.e.,high,medium and low）of P.massoniana plantations were chosen for the analyses.The effects of vertical levels on the water conservation ability were further evaluated based on comparison of the collected data in canopy,litter layer,and soil layer using integrated water storage capacity method.Meanwhile,using the total water source conservation in flood season,the market value method is used to calculate the water conservation service function of P.massoniana plantation in Hubei water source region.These results could provide theoretical guidance and technical supports for the improvement of water conservation capacity and value of P.massoniana plantations near the reservoir.The followings show the detailed results in this study:（1）Both the diameter and high level structure of P.massoniana plantations with different densities show a trend of unimodal curve,close to normal distribution.In the analyzed samples,69 vegetation species,including 32 species of shrub and 27 species of herbs,were recorded.These species can be further divided into 33 families and 62 genera.The major species in P.massoniana plantations with different densities are quite different:in the species of shrub,there is no significant difference in species diversity（P>0.05）,while in the species of herbs,there are significant differences in the E indexes between high density and middle density（P<0.05）.Both the species richness index D and Shannon diversity index H’show the same trend for different densities with low density>middle density>high density.（2）The amount of penetration rainfall in the three densities of P.massoniana plantations ranges from 209.67±38.02 to 232.83±32.76mm,which increases with the increasing atmospheric rainfall.On the other hand,the rainfall penetration rate is about 58～76%,which does not change too much with the increasing atmospheric rainfall.The amount of stem flow ranges from 2.47±0.01 to 5.34±0.35mm,which is positively correlated with the atmospheric rainfall.Furthermore,the stem flow rate ranges from 0.8 to 2.1%,and does not change too much with the increasing atmospheric rainfall.The canopy interception and canopy interception rate vary 56.13±32.40～77.68±38.78mm and 19.26±11.12～26.66±13.31%,respectively,both of which increase with the increase of forest density.（3）The total thickness of litter and litter biomass in the three densities of P.massoniana plantations are about 2.73±0.38～3.99±1.08cm and 12.76±1.67～19.56±3.72t·hm^-2,respectively,with a trend of high density>middle density>low density.The maximum water-holding ability and effective water-holding ability of the litter layer in different densities show the same trend,middle density>high density>low density.The soaking time and water-holding ability in undecomposed litter layer and semi-decomposition litter layer have a logarithmic function relationship（Y=alnt+b,R²>0.9678,P<0.01）.The soaking time and water absorption rate have a power function relationship（V=kt^m,R²>0.9995,P<0.01）.（4）The bulk density of soil within 0～30 cm soil layer in three densities of P.massoniana plantations varies between 1.45±0.04 and 1.54±0.05g·cm^-3,with a total porosity of 42.18±0.43～45.71±1.67%and a soil effective water-holding ability of 2.94±0.78～4.81±0.11 mm.Furthermore,the bulk density of soil has a trend of low density>high density>middle density,total porosity has the opposite trend,and soil effective water-holding ability shows middle density>low density>high density.The p H value of the soil ranges from 5.71±0.09 to6.04±0.13,which is acidic.There is no significant difference among different solid layers with the same density（P>0.05）.With the depth of solid layer increasing,soil organic matter,total nitrogen,total phosphorus,alkali nitrogen,and potassium decrease.The soil infiltration rate and infiltration time with different densities have a power function relationship（Y=at^b,R²>0.97）.（5）The general water source conservation rates of high,medium and low density P.massoniana plantations were 233.19±41.40 mm,237.55±41.58 mm and 204.01±32.64 mm,respectively.Overall,the effective water conservation ability behaves as middle density>high density>low density.Furthermore,average water conservation ability in the areas with the three densities is much higher than the effective water conservation ability.（6）According to the general water source conservation of P.massoniana plantation,the market value method was used to calculate the water conservation value of P.massoniana plantation in the water source region of Danjiangkou reservoir during flood season with an value of 2.16×10⁷yuan.In conclusion,P.massoniana plantations with middle density in Danjiangkou Reservoir have the best water conservation ability.This suggests that it is important to have a reasonable control of the forest density in the process of future forest tending near the reservoir area.