| Aiming to solve the contradiction between demand for the extension of forest vegetation and the limited water supply in sandy land and based on the theory of water resources balance,soil-plant-atmosphere continuum,the dissertation chose the main afforestation tree species of protection forest in Yanchi typical sandy land,such as Atripldex canescen,Caragana microphylla,Caragana Korshinskii Kom,Elaeagnus angustifolia,Tamarix ramosissma Ledeb.,Salix psammophila,Ulmus pumila,Populus alba.,systematically analyzed of the transpiration Characteristics of them,the rules of the transpiration water use and the soil evaporation water use of their wood stands,the actual evapotranspir- ation of the wood lands and the water requirement of them,as well as the soil water shortage of the wood lands,etc..These studies could provide the scientific bases for the selection of tree species and the choice of tree species and vegetation arrangement pattern.The dissertation involved two aspects:1.Water Consumption Characteristics of Trees and environmental water capacity of protection forest in Yanchi Sandy Land:(1)The simulation and prediction of stand transpiration and water consumption;(2)The vapotranspiration Characteristics of stand and the suitable soil moisture condition of tree growth in sandy land;(3)Water requirement of forest tree,plant coefficient of forest tree and environmental water capacity of protection forest;2.Structure Installation and effects in conrolling wind of Protection Forest in Yanchi Sandy Land(1) Field observation on effects of typical farmland shelterbelts in controlling wind and sand in the sandy land of Yanchi;evaluation of protection function of shelter belts;(2) The effects in conrolling wind and sand of different disposition structure of farm land shelterbelts;(3) The disposition vegetable structure combining trees with grasses.Major conclusions are summarized as follows:1.Based on Penman Monteith method and probe system way,the evaporation of the forest stand can be accurately calculated.By two ways,the evaporation of the forest stand in experimental zones from 2005 to 2006 was calculated:Salix Psammophila(182～196mm),Tamarix ramosissma Ledeb.(177～186mm), Elaeagnus angustifolia(159～182mm),Caragana Korshinskii Kom(138～143mm),Caragana microphylla(128～134mm),Atripldex canescens(112～130mm) is the sequence of annual transpiration water use.The amount of annual transpiration water use of single Ulmus pumila is 0.5 time fewer than that of a Populus alba.2.The model of the relationship of the soil evaporation of wood lands(Z) with the free water surface evaporation(X) and the soil moisture(Y) was established based on the investigated data.Based on Water Consumption of four shrubs and two arbors of whole growing season in 2006 and soil evaporation of forest land,calculating the actual evaporation.The actual evaporation of Atripldex canescen,Caragana microphylla Lam,Caragana Korshinskii Kom,Elaeagnus angustifolia,Tamarix ramosissma Ledeb.,Salix Psammophila,Ulmus pumila L,Populus alba.respectively is 298mm,291mm,287mm,338mm,331mm, 329mm,334mm and 427mm.3.Study on the relation among photosynthesis rate,stomatal conductance,transpiration rate,water use efficiency and soil water content.Based on the result and parameter,we choose the suitable SWC of Salix Psammophila Elaeagnus angustifolia is 10.72%～14.36%,Elaeagnus angustifolia is 9.12%～11.40%, Caragana microphylla is 11.39%～13.20%and Atripldex canescen is 10.07%～12.20%.4.Under suitable soil moisture,the lower limits of annual water requirements during the growth season (from May to October) of Atripldex canescen,Caragana microphylla Lam,Caragana Korshinskii Kom, Elaeagnus angustifolia,Tamarix ramosissma Ledeb.,Salix Psammophila,Ulmus pumila L,Populus alba. respectively is 387mm,437mm,436mm,445mm,447mm,459mm in the sandy land.5.The least water nourishment area(S) for a tree growth in the sandy land of Yanchi was as follows: 15m2 for a Ulmus pumila and 20m2 for a Populus alba.The least water nourishment area(S) for a tree growth in the sandy land of Dalate was as follows:7m2 for a Elaeagnus angustifolia;4m2 for a Salix Psammophila,a Caragana Korshinskii Kom,a Tamarix ramosissma Ledeb,a Caragana microphylla Lam and a Atripldex canescens.6.Stand structure and vegetation arrangement pattern is important factor influencing effects of farm land shelterbelts in conrolling wind and sand.Field observation on effects of typ ical farmland shelterbelts in controlling wind and sand in the sandy land of Yanchi in Ningxia revealed that the shelterbelt of Caragana m icrophylla shrubberies provided shelter over the woodlot perse and 0-3H(H stands for tree height) at the leeway edge of the forest,with a limited effective range in the leeway;that the wind speeds at both windward side and leeward side of the shelterbelt of Salix psamm ophila were greater than the threshold velocity(4.53 m·s-1) of sand rising,so the shelterbelt gave little protection of the farmland;and that the fragmentary shelterbelt of Ulm uspumila,was unable to play its wind-breaking role.Sands accumulated on the leeway side of the latter two shelterbelts,indicating that they could not effectively prevent aeolian sands from coming into the farmland,while sands arrested inside the belts of Caragana microphylla,showing its effectiveness in controlling aeolian sands.
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