| Rational utilization of water resources is the rigid constraint of ecological construction in the Loess Hilly region.To optimize the layout of forest and grass vegetation,the contradiction between vegetation water and water resources needs to be solved.Over the years,a large area of artificial forest and grass vegetation has been created in the Loess Hilly Region of Ningxia,achieving good vegetation restoration results.However,there are also obvious problems such as single species configuration,unreasonable vegetation structure,and the degradation of artificial forest and grass in some areas.The main reason is that the contradiction between vegetation water and water resources has not been fundamentally solved.Exploring the ecological and hydrological processes of typical forest and grass vegetation,clarifying the ecological and hydrological processes and functions of forest and grass vegetation in loess hilly area,can not only provide scientific decisions for further optimization of forest and grass vegetation structure in the area,but also meet the needs of ecological protection and high-quality development in the loess hilly areas.This article takes the Zhongzhuang Basin in Pengyang County,Loess Hills District,Ningxia as the study area,and takes six typical forest and grass vegetation as the research object.Based on positioning monitoring,correlation analysis,regression analysis,and other methods are used to study hydrological factors such as forest canopy interception,litter layer water retention,soil layer infiltration,and water content changes.The Brook90 model is selected to simulate the ecological and hydrological characteristics of typical forest and grass vegetation,and a comprehensive evaluation of the ecological and hydrological functions of different forest and grass vegetation was conducted using the Analytic Hierarchy Process.Then the optimal forest and grass vegetation type was selected.The research results have important guiding significance for promoting sustainable management of forest and grass vegetation in the loess hilly area of Ningxia,and achieving high-quality development of ecological construction.The main research findings are as follows:(1)The ecological and hydrological characteristics of six typical forest and grass vegetation types were analyzed,and the overall performance of canopy interception rate was better in mixed forests than in pure forests.The canopy interception rate is best in the Armeniaca sibirica-Amygdalus davidiana-Alfalfa mixed forest(3.30%),followed by the Armeniaca sibirica-Hippophae rhamnoides mixed forest(3.25%),and the Caragana pure forest is the smallest(1.59%).A mixed forest with multiple tree species configuration has a high vegetation canopy density,which increases the interception rate of the canopy and enhances the ecological and hydrological functions of the forest canopy.(2)The ecological and hydrological characteristics of the litter layer of six typical forest and grass vegetation types were revealed,and the overall interception capacity of the litter was the best in the Armeniaca sibirica-Caragana mixed forest(7.67 t/hm~2)and the Armeniaca sibirica pure forest(11.08 t/hm~2).The total accumulation of litter ranges is between 1.05 and 4.01 t/hm~2,the maximum water capacity is between 3.67 and 15.75 t/hm~2,and the maximum water holding capacity ranges is between 182.90 and 264.65%.The composition of tree species is the main factor affecting the accumulation and retention capacity of litter,and the vegetation types of pure apricot forests and mixed apricot forests are more conducive to enhancing the hydrological function of the litter layer.(3)The ecological and hydrological characteristics of the soil layer of six typical forest and grass vegetation were elucidated.The overall ecological and hydrological functions of the mixed forest soil layer were better than those of the pure forest,with the best effect being the Armeniaca sibirica-Caragana mixed forest.The soil bulk density of mixed forest is lower than that of pure forest,and the soil capillary porosity,non-capillary porosity,and total porosity all show that mixed forest is higher than pure forest.The range of soil moisture change is between 5%and 20%,and the average soil moisture and storage capacity of the Armeniaca sibirica-Caragana mixed forest is the highest.The soil infiltration performance of the Amygdalus davidiana pure forest and the Armeniaca sibirica-Caragana mixed forest are superior to other forest and grass vegetation types.Mixed forest is superior to pure forest in changing soil water holding capacity,infiltration characteristics,soil evaporation characteristics,and soil moisture characteristics,especially in the the Armeniaca sibirica-Caragana mixed forest.(4)Six typical forest and grass vegetation types were simulated for ecological hydrological processes,further validating the main factors affecting ecological hydrological processes and rainfall redistribution.Selecting the Brook90 model and combining the characteristics of the study area for parameter optimization and simulation,the proportion of soil infiltration in the total precipitation distribution process is 79.66%to 94.65%,which is the main distribution direction of precipitation,followed by the interception of precipitation by vegetation canopy and surface runoff.The R~2for soil moisture content determination ranges from 0.74 to 0.91,RMSE ranges from 1.32%to 2.32%,and NRMSE ranges from 8.15%to 16.33%.The consistency and accuracy of the determination are good.The calibrated model was further verified by using the measured soil moisture data in 2022.The simulated absolute error and relative error of soil moisture were within±5%and±20%,respectively.The simulation effect was good,indicating that the calibrated model can be used to simulate the hydrological process of different forest and grass vegetation.(5)A comprehensive evaluation was conducted on the ecological and hydrological functions of six typical forest and grass vegetation types.The ecological and hydrological functions of mixed forests are generally better than those of pure forests.The tree shrub mixed model,mainly composed of mountain apricots,should become the direction for optimizing the vegetation structure in the study area.Combining the measured data with the model simulation data,The Analytic Hierarchy Process(AHP)was used to comprehensively evaluate the ecological and hydrological functions of different forest and grass vegetation in the loess hilly region.The quantitative score of the comprehensive evaluation was as follows:Armeniaca sibirica-Caragana mixed forest(0.765)>Armeniaca sibirica pure forest(0.753)>rmeniaca sibirica-Hippophae rhamnoides mixed forest(0.726)>Armeniaca sibirica-Amygdalus davidiana-Alfalfa mixed forest(0.684)>Amygdalus davidiana pure forest(0.622)>Caragana pure forest(0.577).In summary,the quantitative values of the ecological and hydrological functions of different artificial forest and grass vegetation in the Loess Hilly Area of Ningxia are between 0.577 and 0.765,which is at a high level.This fully indicates that through the restoration of forest and grass vegetation in the Loess Hilly Area of Ningxia,the regional water conservation function can be improved,especially in the construction of a mixed tree and shrub model dominated by apricot,which has the best ecological and hydrological functions and can be used as a direction for the construction and structural optimization of forest and grass vegetation in the area. |
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