Assessment On Soil And Water Conservation Function Of De-farmed Bamboo Plantations In South Sichuan Province

Bambusa(B) rigida and Bambusa pervariabilis×Dendrocalamopsis(D) daii are theimportant part of sympodial bamboo resource in China, while also belong to the importantbamboo species for economic in southern of China, furthermore, they are not only havingfaster growing and higher yields, but also have obvious advantage in the field of paper making,weaving, fiber utilization et al; Therefore, the irreplaceable role is played in the developmentof China's bamboo industry. Southern of Sichuan province is located in the upper reaches ofthe Yangtze River, rich in rainfall, however, due to the unreasonable reclamation andcultivation of steep slopes over the years, soil degradation and soil erosion is becoming moreand more serious. And because of their good economic value and ecological function, B.rigidaand B. pervariabilis×D. daii which as the local common species of bamboo, were widelypromoted and application at the period of Grain for Green Project (GTGP).In order to explorethe water and soil conservation function of de-farmed plantation of bamboo, the methods offield observation and indoor test were taken to systematic analysis community structure and thefeature of productivity, soil properties, water conservation features, soil resistance to erosionand economic benefits of stands which included5-year(Y5) and10-year(Y10) de-farmed B.rigida plantation,5-year(C5) and10-year(C10) de-farmed B. pervariabilis×D. daii plantation,and the control-managing B. rigida plantation (YCK1), B. pervariabilis×D. daii plantation(CCK2) and slope farmland (NCK0). Based on the analysis mentioned above, the comprehensiveindex evaluation system of ecological functions and economic benefits of de-farmed bambooforests was established, and then, the assessment result of different stands was obtained by thissystem. The aim was to provide a theoretical basis for the choice of bamboo species andsustainable management of de-farmed land in south Sichuan province.The main conclusionsare as follows:1The differences of community structure and the feature of productivity among differentplots were significant. The results showed that Y5had lower bamboo diameter at breast height(DBH) and height than Y10and YCK1, while C5was better than C10and CCK2, so, B.pervariabilis×D. daii need less time than B. rigida when they grew up to forset. In addition, there was a significant relationship between DBH and tree height both in B. rigida and B.pervariabilis×D. daii, and the regression equation is H=2.29D+0.670and H=0.939D+5.813.Richness index and evenness index of species diversity were reduced with the increase ofde-farmed years, and the order of species diversity level was: herb layer> shrub layer> treelayer. Biomass in different stands are differ with B. rigida and B. pervariabilis×D. daii forests,and the average individual biomass order was YCK1(3.65kg)> Y10(3.48kg)> Y5(3.18kg)and C5(4.31kg)> CCK2(4.01kg)> C10(3.50kg)respectively. In study region, all the standsbiomass could be excellent simulated by relative growth model: W＝a(D2H)b.2Soil quality and soil properties could be improved by returning farmland to bambooforest. The soil quality of different stands had been evaluated through weighted compositeindex method (WCIM), the comprehensive index order of B. rigida was Y5> YCK1> NCK0>Y10,and B. pervariabilis×D. daii was C5> C10> NCK0> CCK2,5-year de-farmed forests had bettersoil quality than the other stands, because they had better water-holding capacity, soil porosity,and higher content of chemical elements. The main nutrient elements were difference betweendifferent de-farmed time forests, the content of N and K decreased with the increasing ofde-framing time, but P had opposite trend.3Bamboo species and de-farmed time were closely related to water conservation functionof canopy layer, litter layer and soil layer of forests. The average interception rate of canopyaccount for39.31%of the amount of water conservation, and the order of B. rigida wasY5>Y10>YCK1, the best was Y5, account for15.24%of rainfall; the order of B. pervariabilis×D.daii was C5>CCK2> C10, C5account for15.68%of rainfall. Leaf area index was ranged from1.253to3.419, and it also had a significant positive correlation with canopy interceptioncapacity. Water-holding capacity of litter layer account for0.68%. The order of B. rigida wasY10>YCK1>Y5, and B. pervariabilis×D. daii was C10>CCK2>C5. Litter storage, and its maximuminterception capacity and effective interception increased with the increasing of de-farmedyears. Immersion experiment also showed that the fitting models between immersion time (t)and litter water-holding capacity (S), water absorption rate (V) were S=k lnt+p and V=k tn. Thesoil layer is the main body of water conservation, accounting for57.62~62.50%of the wholebamboo forest water conservation, the sequence B. rigida was Y5(2997.24t·hm-2)>YCK1(2447.86t·hm-2)>Y10(2381.67t·hm-2), and B. pervariabilis×D. daii was CCK2(2709.28 t·hm-2)>C5(2680.54t·hm-2)>C10(2250.93t·hm-2). So, in the aspect of water conservation,for B. rigida, Y5was the best (487.09mm), Y10taken the second place (413.33mm), and thelast was YCK1(403.92mm); for B. pervariabilis×D. daii, C5>CCK2>C10, respective value was461.35mm,433.51mm and378.32mm.4De-farmed plantations had better soil anti-erodibility than farmland, and increased withthe extending of de-farmed time. The order of soil anti-erodibility under B. rigida stands wasY10>YCK1>Y5>NCK0, enhanced68.35%,39.26%and37.77%than farmland, respectively, andthe order of B. pervariabilis×D. daii was C10> CCK2>C5>NCK0, enhanced44.63%,43.05%and22.67%separately.10-year de-farmed plantations were the best than the other stands insoil anti-erodibility. Thus, de-farming can significantly improve the ability of soilanti-erodibility, and the longer de-farmed times, the higher soil anti-erodibility level enhanced.In addition, principal component analysis and factor analysis of different anti-erodibilityindexes indicated that content of water stable aggregates, soil permeability, the mean weightdiameter and geometric mean diameter had existed significant or highly significant correlationwith soil properties, soil anti-erodibility indexes, so they can be used as a comprehensivelyquantitative index to evaluate the soil erosion resistance5Main ecological functions of different bamboo forest were quantitative evaluated byWCIM, the results showed that the decreasing order of it in different B. rigida wasY5>YCK1>Y10>NCK0, and the B. pervariabilis×D. daii was C5>CCK2>C10>NCK0,5-yearde-farmed stands had the best ecological functions, then were management plantations, and thelast were10-year de-farmed stands. However, both of de-farmed stands had not reachedsignificant level to control, respectively, in addition, forest stands had better ecologicalfunction than farmland. In economic benefit aspect,10-year de-farmed plantation significantlyhigher than5-year de-farmed plantation and farmland.In a word, in the respect of bamboo emerging rate, biomass rate of culm and the value ofbamboo wood, B. rigida are better than B. pervariabilis×D. daii, meanwhile, it has moreadvantage on improving soil quality and water conservation of forest, but it needs to spendmore time to grow up to forest, and also has lower biomass than B. pervariabilis×D. daii.Regard to B. pervariabilis×D. daii, besides higher individual biomass and DBH, it has betterability on canopy interception and fast growth either, superadded its high soil anti-erodibility, B. pervariabilis×D. daii could also belong to a better ecological construction species of bamboo.