Study On Characteristics Of Runoff And Soil Erosion Under Different Stand Conditions In The Middle Tianshan Forestry

In this paper, based on Tianshan forest ecosystem position research station, from June to September in2012, using runoff plots method, with shrubbery13kinds of natural forest stand (against bare land,grassland) in the middle tianshan forestry plantation as the research object, monitor and analyze the soilerosion, rainfall kinetic energy in the test areas and the slope runoff, runoff time process, production flow,sediment yield characteristics in each stand condition, quantitatively evaluate the soil and waterconservation function of each forest condition, and use the brook90model to simulate the upstreamwatershed forest change on surface runoff in the studied area. The research results are as follows:(1) During the study period but less rainfall kinetic energy during rainfall difference is bigger, andrainfall runoff process presents the corresponding relation, rainfall intensity and runoff time correlation isobvious. The surface runoff in the study area is given priority to with super infiltration runoff.On runoff ofeach forest type, the affecting sequence is bareland>grassland>middle-aged forest>middle-agedforest1>plantation1>shrub forest2>shrub forest1>young forest>plantation2>plantation3>mixedforest>middle-ages forest3>near mature forest>mature forest>middle-aged forest. Bareland and woodlanddifference between6.23-11.23m3/hm2, each stand difference between1.21-5.09m3/hm2, natural forestsurface runoff reduction rate is35%-100%, planted forest was30%-90%, shrubbery was40%-80%.(2) On sediment yield: bareland>grassland>middle-aged forest2>middle-aged forest1>youngforest>shrub forest2>plantation1>shrub forest1>plantation3>mature forest>plantation2>mixedforest>middle-aged forest4>near mature forest>middle-aged forest3. Bare2to6times that of woodland,forestland between1-2.5times. sediment reduction rate from20.6%to100%of natural forest andplantation is in26.3%-91.5%, shrub land between40%and70%.(3) Runoff yield significantly correlation with rainfall and sediment yield significantly correlation withrainfall intensity and sediment yield exponential function relation and production flow.(4)Using the grey correlation analysis method to analyze the influence factors of runoff and sedimentyield, get the result that impact on sediment yield, rainfall> forest density> the height of the canopy livingbranch> litter thickness> canopy density>slope, while on runoff, rainfall> litter thickness> canopy density> forest density> the height of the canopy living branch> slope. For the impact strength that differentstand conditions having on the runoff and sediment yield, natural forest appears: middle-aged forest3>near mature forest> middle-aged forest4> mature forest> young forest1> middle-aged forest2>middle-aged forest1;in plantation: mixed forest> translucent cutting upbringing forest> pruningupbringing forest> not upbringing forest; in shrub: Cover0.6> Cover0.8.(5)Using the principal component (PAC) analysis of forest water conservation function is evaluated,the results showed that forest stand growth factor played a leading role in the evaluation of waterconservation in the study area; Age for mid-maturation and near mature forest, forest density in1100-1400plants/hm2, crown density in0.6-0.7, trees in16to18m tall, DBH(diameter at breast height) growthbetween20-23cm under natural forest water conservation functions to achieve the best; plantation mixedcomposite layer water conservation effect than monolayer, artificial forest canopy density of0.6-0.8, thedensity of2000-2200plants/hm2, better water conservation function. Crown density and stand density candirectly reflect most stand growth, so the stand density and production flow, sediment yield; Crown densitywith sediment yield, production flow, the relationship between rainfall factors to function fitting.(6) Using brook90models to simulate the surface runoff of small watershed in study areas. Studyingthe model of stand condition changes caused by surface runoff was simulated. The results showed that:after grass or bare land become into woodland or shrubbery, runoff can be reduced by10%-25%,plantation grown turning into middle-aged forest3can get30%reduction of runoff.