Study Of Hrdrological Characteristics For Artificial Black Locust Forest In The Loess Hilly And Gully Region Of China

With the implementation of ecological projects such as Grain for Green Project,vegetation restoration got notable effect in the Loess Plateau.On one hand,large-scale vegetation restoration increased the soil moisture consumption in this region,on the other hand,vegetation canopy and litter interception decreased soil moisture coming into soil.And affected by individual rainfall characteristic,the process of rainfall-interception-soil water quite complicated.The system study of vegetation hydrology characteristic and influencing factors can promote further understanding of hydrological cycle process,which is important to region ecological restoration and optimized utilization of water resources.Therefore,the study takes Zhifanggou watershed in Ansai county,Shaanxi province,which is a typical small watershed in the loess hilly and gully region,as the study area.The black locust,a typical and widespread vegetation of Grain for Green Project,were selected as the main research ecosystem.The rainfall partitioning of canopy of the black locust,water retention of forest litter,surface runoff,the spatiotemporal pattern of soil moisture,and the effects of rainfall,vegetation,and their synergistic on soil moisture were studied.The main results are as follows:(1)Rainfall amount of Zhifanggou watershed were 149.0 mm,527.0 mm and 574.2mm in the study period of August to October of 2018,May to October of 2019 and 2020,respectively.The short-duration(<6 h)and low-intensity(0?2.5 mm/h)rainfall are mainly in the Zhifanggou watershed,while the contribution of rainfall amount mainly from long-duration(?6 h)and low-intensity rainfall events.(2)The throughfall percentage,stemflow percentage,and canopy interception loss percentage of artificial black locust forest were 71.76%,1.90%,and 26.34%,respectively for measured 23 rainfall events in study period.Throughfall percentage decreased with the canopy height decreasing,while it increased with the distance to trunk increasing.Throughfall and stemflow showed significant linear correlation with rainfall amount,while the canopy interception loss showed a power function increased with rainfall amount increasing.The critical condition for black locust forests to produce throughfall and stemflow is 2.76 mm and 5.00 mm,respectively in this study region.The effects of vegetation characteristics(leaf area index,tree height,diameter at the breast,canopy width and canopy openess)on throughfall,stemflow and interception loss has a difference because of the difference of rainfall amount.(3)The natural water content and maximum water-holding rate of artifical black locust litter was 66.25%and 331.74%,respectively,and the maximum water holding capacity of litter were 6.36?9.08 t/hm~2.The interception percentage of litter on natural rainfall under the natural condition between 9.83%and 65.59%.The exists a very significant power function relation between interception of litter and rainfall amount(R~2=0.92),and it can be fitting by a second-degree polynomial with rainfall duration and rainfall intensity.The change of surface runoff and rainfall amount were basic aggrement with time,where the average of surface runoff coefficient is 0.05.(4)Compared with caragana and wasteland,the artificial black locust consumes more soil moisture,where soil moisture content of 0?300 cm soil profile was 6.88%(volume,the same below).The soil moisture has significant difference at different soil depth with time variations during the growth season(May to October),which maximum values appeared in September.Soil moisture content of black locust lower at 80?180 cm soil layer,and it increased with the distance to trunk increasing.Soil moisture content of surface layer(0?20cm)is more susceptible to rainfall characteristics.The better correlation of vegetation characteristic(tree height,canopy width,diameter at the breast,leaf area index and canopy openess)and soil moisture content with rainfall amount increasing.(5)The black locust forest has a relatively weak ability of water conservation function,which a comprehensive evaluation score was 0.5199(the score closing to 1,the function changing better).In the growing season of 2019,the canopy interception of black locust is1388.1 t/hm~2,while the soil moisture supplementation is only 28.0 t/hm~2.Therefore,we think that reduces the canopy interception of rainfall by canopy management,the problem of forest soil dryness in this area can be effectively alleviated.