The Study On Architecture And Wind Break Efficiency Of Imitation Sand-Fixed Shrub

The32.8percent of total territory of China is located arid region with a common and strong harm from wind and sand. It is important to control wind-sand disaster for developing region economy and improve resident quality in arid area of China. As less water resource, it was still a main method in arid region to set up the sand barrier for controlling wind-sand harm. It would be worth to research and develop a new material and techniques on integration and experiment at harm area of arid region for the implement on enhanced function of control desertification damage, and a urgently task on wind-sand action, control wind and sand harm, especially the connection between structure of shrub and wind-sand flux. It would boost the study and give an actuality improve to support control theory of plant, design and management of combating project on wind-sand, disaster prevention and control and evaluation of engineering of combating wind and sand harm. The control efficiency of simulation shrub forest was effected relatively the wind-sand action and combating damage of wind and sand by an investigation in simulated plant of field and reference simulated experiment in wind tunnel. The architecture of seven shrubs and simulation shrub was measured in field and wind tunnel at Gansu Minqin National Studies Station for Desert Steppe Ecosystem with the Minqin Desert Botanical Garden and Sha Potou Desert Study Station. It was discussed that the architecture index of simulation shrub and the efficiency of simulation shrub forest to defend wind and sand damage. The architecture and ordination of branchs the relation between architecture of simulated shrub and wind-sand action, vertical and horizontal wind velocity, transporting sand, aeolian and traped sand were measured and aerodynamic roughness, structure of sand cloud and ratio of sand dischange were calculated. The simulated shrub, which modeled the shrub, combined goodness of constructions of psammophyteses with adaption architecture at wind-sand environment, and the techniques of control wind-sand disaster by simulated shrub that was a chemistry control wind-sand, as well as control wind-sand by biological method. It was not limited to establish windbreak for denfending wind-sand by forest that would be supplied by simulated shrub and gived a material for study on mechanism of desert control by shrub. The results were as follows to be taken by the study in field and wind tunnel on simulation shrub.1) The architectures of Haloxylon ammodendron, Hedysarum scoparium, Calligomtm mongolicum, Nitraria tangutorum, Reaumuria kaschgarica, Artemisia ordosica and A. arenaria were divided into two categories, as well as the branch ordination, which affected the ability to control wind-sand by shrub.(1) According to the biological characteristics such as leaf, Nitraria tangutorum was category with relative big leaf, and the others were classified into a type with especial leaf. Reaumuria kaschgarica, Nitraria tangutorum, Artemisia ordosica, Hedysarum scoparium, would be classified into a shrub with dense branching architature, as well as the spacing architecture of Haloxylon ammodendron, Calligonum mongolicum, Artemisia arenaria.(2) On the basis analysis of branche ordination,65.0%of branching angle was25°～50°. The changes of different grade branch's branching angle of shrub with leaf, were bigger than that of shrub with especial leaf. The mean of branching angle of seven shrubs was gradually bigger from inside to outer position of canopy. The branch ordination of all of seven shrubs was divided into four degrees, according to proportion of branching by degrees rate. The branch length of all observated shrubs was mainly5-30cm. The outer branches of canopy of Artemisia ordosica, Hedysarum scoparium, Calligonium mongolicum, Nitratia tangutorm and hololachne soongarica were shorter than that of ins id banches. It was shrub, such as Haloxylon ammodendron and Artemisia arenaria, that outer branches were gradually longer than that of middle branch and inside. The count of branching fractal dimension of shrubs observed all of was decimal, which showed that increased degree of length of branch decrease with that of branch length increase, and would not devided secondary branch as branch length achieved a certain value, but it had one branch at least. Except Haloxylon ammodendron, all of branching rate of six shrubs were smaller than one, which showed that branching distribution of the six shrubs was dense outside whereas thinned inside of canopy. The collection quantity of sand related with percent of windward density of branch distribution as20%-30%, and relatively collected larger number of sand.(3) The outline of Nitraria tangutorum and Reaumuria songarica was like a bomb one with the widest at the height of10cm, while the grade of change upwind projected area with height of Reaumuria songarica is smaller than that of Nitraria tangutorum. The canopy of Hedysarum scoparium, Haloxylon ammodendron and Artermisia sphaerocephala was like spindle with the widest at the height of20-40cm. It was opposite with measured other shrubs that wide of upwind projected area of Calligonum mongolicunl increase with height of canopy which showed the widest at the top and almost a shape like a broom.2) The simulation sand-fixed shrub was maded from polymer materials, and simulating architecture of sand-fixed shrub. The two kinds of simulation sand-fixed shrub modeled natural shrub were produced which one was simulation shrub with leaf, and another leafless simulation shrub, according to configuration and branching architecture. The simulation shrub had advantage of sand barrier and sand-fixed shrub. It could be a method to establish shelterbelt alone or collocate with other sand barrier or rain-fed vegetation by simulation shrub.The biological sand-control system and sand barrier was complemented by simulation shrub.(1) The branch ordination of simulation shrub should progressively reduce from the inside to outside of canopy, and the grade of general branch ordination was3-4levels. The branch angle of simulation shrubs should be better between25°to50°. The branch angle progressively became bigger from grade to grade at the inside to outside of canopy. The simulation shrub with leaf would be composed with lanceolate leaves at length of4-7cm, without trunck at height of5-50cm, and tall of50cm. The leaves connect directly the primary branch without secondary branch, which formed simulattion shrub with alone roots without the secondary branch ordination. The height of simulated shrubs without leaves is40cm, it can be divided into three-level branch ordination, the third-level branch all concentrate on the roots; the two kinds of simulated shrubs take the steel wire as its body, it has flexibility, is arbuscular without trunk.(2) The shape of simulation shrub was hemispherical canopy whith architecture of sparse inside and dense outside. The branch density of upwind projected area would be not less than0.25-0.50, and it was half that upwind projected area equal the canopy area of0.50-0.78m2. The simulation sand-fixed shrubs could be established windbreak by themself and combined sand-fixed forestry system with shrubs.3) Compared the impact on the wind velocity and the magnitude of transported and accumulated sand in experiment in the field and wind tunnel, it determined that the simulation shrubs increased the surface roughness, reduced the wind velocity, weakened wind power, and intercepted movement sand, and had evident function to control wind and fix shifting sands.(1) The wind velocity, surround the simulation no-leaf-shrub and the leaf simulation in the field, as well as Artemisia arenaria, decreased relatively with wind velocity increased. Under the different wind velocity grade, the ratio of weakened wind velocity of the simulation shrubs was different. At height of20cm, it was biggest ratio of75.08%to decrease wind velocity by no-simulation leaf-shrubs, as well as50.23%of the simulation leaf-shrubs. It was relatively large that simulation leaf-shrubs decraese ratio of wind velocity at the wind velocity more than5m/s. The average ventilation coefficient of the leaf and no-simulation leaf-shrubs was more than50%, and the largest was92.23%, while less than the ventilation coefficient of Artemisia arenaria.(2) The range of accumulating sand of simulation no-leaf-shrubs was up to0.5m2. The volume of accumulating sand of per simulation shrubs was about three times of its canopy volume, and shape accumulated sand of no-simulation leaf-shrubs with its center look like a discoid. The simulation leaf-shrubs formed a funnel-shaped accumulated sand shape, and the sand volume of per simulation leaf-shrubs was approximately1.04times of its canopy volume.(3) Windbreak efficiency of simulation no-leaf-shrubs forests was lower than the simulation leaf-shrubs forests, while efficiency of both increased with the wind velocity. At the wind velocity was8.0-10.7m/s, the rate of reducing the wind velocity of the simulation leaf-shrubs forest was about1.5times that of the simulation no-leaf-shrubs forest. At different wind speeds and at different heights, the difference of weakening the average wind speed of two kinds of simulation shrubs was significant. The wind velocity of two simulation shrubs forests had exponent function relationship with a high degree of change, and the roughness of simulation shrubs forest was more two times of that shifting sand-land.(4) The average reducing ratio of wind velocity of simulation shrubs+Haloxylon ammodendron forest was less than that of the plastic checkerboard barrier. Nevertheless, the compared ratio decreasing the wind velocity between simulation shrubs and plastic checkerboard barriers was less with the wind speed increasing. At8.1-8.9m/s of wind velocity, the ratio of decreasing wind velocity of the simulation shrubs was80%of plastic checkerboard barriers. At height of20cm, the transporting rate of Haloxylon ammodendron+simulation shrub forest was exponential decline correlation coefficient with height changes. The average transporting rate of the pure sand-land was4.13times of the Haloxylon ammodendron+simulation shrub forests. At moving sandland, the transport ratio of sand was measured. The results shown the transporting rate of sand in simulation shrub forest increased with the dencity of forest was less. The average transporting rate of the pure sandland was1355.70times of the simulation shrub forests with1.5×2.0m of spacing in the rows and spacing between rows.(5) At the7m/s,9m/s, of12m/s, and15m/s of wind velocity of laboratory, six deceleration zone and four acceleration zone of wind velocity were formed around simulation leaf-shrubs. The number of main branches of simulation shrubs was16-20branchs. The performance ratio of wind and sand prevention was relatively large with transparence degrees30%-40%of simulation leaf-shrubs. At different wind velocity, sand transport ratio of sand was relatively less, which was compared with better simulation shrubs architecture.