Optimization Of Vegetation Distribution In Small Watershed In Loess Plateau

The Loess Plateau-Qinghai-Tibet Plateau transition zone has long been considered as the most fragile and most rapidly changing region in the world's ecological environment.The successive implementation of national key forestry ecological projects such as the Three North Shelterbelt,the protection of natural forests and the conversion of farmland to forests has significantly increased forest coverage and improved the ecological environment in the area.However,the simple increase in forest area and volume,lacking of scientific forest allocation and reasonable forest density guidance.After artificial planting,the problems of low survival rate,low retention rate and low benefit appeared.The economic and ecological benefits of"three low forests"are poor,which cannot give full play to the function of shelterbelt to conserve water and protect water and soil.On the contrary,over-dense forests cause dry soil layer,destroy the circulation and balance of regional water resources,and increase the difficulty of afforestation.development of.It can be seen that on the basis of fully understanding the scientific issues of forestry and water,the reasonable spatial allocation of forest vegetation in small watersheds has become a key issue urgently to be solved in forestry construction.Especially in water-restricted ecosystems,the carrying capacity of soil moisture vegetation determines the composition,density,structure and spatial distribution pattern of forest vegetation communities.Therefore,how to carry out the space of vegetation on the basis of fully quantifying the carrying capacity of soil moisture vegetation Allocation is the core issue of vegetation construction and restoration in future small watersheds.In this paper,a small watershed located in An Mentan,Datong County,Qinghai,is used as the research object.The spatial allocation optimization of water conservation forests based on soil moisture and vegetation carrying capacity is carried out.First of all,using the measured and collected data,the optimal The best forest coverage rate;then,the mathematical classification method was used to divide the site types of small watersheds,and the results were implemented to specific plots in the entire watershed based on the Arc GIS technology platform.Finally,based on the alignment of different site types and soil moisture and vegetation carrying capacity,the types of vegetation and their density or coverage under different site conditions were determined.The main conclusions are as follows:1)This paper takes the function of water conservation of forest vegetation as the goal,and calculates the optimal forest coverage in the small watershed based on the equilibrium relationship between the saturated soil water storage capacity of the forest in the small watershed of An Mentan and the daily maximum rainfall in the area for 20 years.The results show that:based on the current soil saturated water storage of the main forest types in the An Mentan watershed,the optimal forest coverage in the small watershed is 24.46%.2)Apply statistical methods to study and divide the site types in the small watershed of An Mentan.Principal component analysis and related analysis results show that slope,aspect,and altitude are the dominant site factors that affect site type classification;a systematic clustering analysis of dominant environmental factors and vegetation factors,and use of aspect-slope-elevation for site types The three-stage naming method can divide small watersheds into five site types:Sunny gentle slope low altitude site type(T1),shady steep slope low altitude site type(T2),shady slope low altitude site type(T3),and Yin moderate Altitude site type(T4),shady slope high altitude site type(T5).3)To determine the soil moisture and vegetation carrying capacity under different site conditions,it is necessary to fit the functional relationship between vegetation LAI and soil recharge and consumption.Based on this,the relationship between vegetation LAI of different site types,soil replenishment,and soil moisture content is established:The function of site T1 is:Y supplement=-73.919L+270.25,Y consumption=37.822L2-69.038L+233.02;site The function of T2 is:Y supplement=-588.44L+256.27,Y consumption=159.53L2-175.99L+266.13;The function of T3 is:Y supplement=-49.396L+260.1,Y consumption=37.291L2-63.13L+252.78;The function of Site T4 is:Y supplement=-82.801L+275.45,Y consumption=80.424L2-104.26L+256.27;The function of Site T5 is:Y supplement=-48.581L+275.57,Y consumption=179.68L2-146.60L+239.3.The results showed that the soil water replenishment and LAI of each vegetation type had a very significant negative correlation(R~2>0.901,P<0.01).The larger the vegetation LAI,the smaller the soil replenishment;the soil water consumption and LAI were both The binary function relationship was significantly related(R~2>0.857,P<0.05).With the increase of vegetation LAI,soil water consumption decreased first and then increased.At the same time,there are thresholds for these relationships.It is expected that when the LAI continues to increase,the soil replenishment will decrease to a fixed minimum,which will remain unchanged,and the soil consumption will also remain unchanged as the LAI increases to a certain value.The LAI of the plots in the study area are at a low level,so they are not shown in the functional relationship.4)In order to obtain the soil water and vegetation carrying capacity under different site conditions,this year uses the maximum LAI to represent the soil water and vegetation carrying capacity.Through the principle of water balance,the amount of soil water replenishment is equal to the soil water consumption,and the maximum vegetation of each site type is obtained.LAI,in order:0.64,0.81,1.12,0.69,1.06.Combined with the stand space allocation and growth status of different site types,some optimization suggestions for the space allocation of existing vegetation in small watersheds are proposed.