Studied The Tree Spatial Structure And The Wind Break Function On Psammophytes In MinQin Country

Resorting vegetation by enclosure is an effective measure to resolve desertificated land. Resorting vegetaion as an important part of desertification control by vegetation is a less invested and effective measure. But it needs longer years to recover in natural conditon. The massive planting is controled by water in arid and semi-arid desert. So, it's much more important to study afforesting in certain area, espicialy the wind break and sand fixation of isolated planting. The Holoxylom ammodendron Bunge, Hedysarum scoparium Fiseh.et Mey, Caragana korshinskii Kom and Calligonum mongolicum Turcz are used for desert planting in Minqin county.Studying on spatial structure and wind break fuction of 4 psammophytes Holoxylom ammodendron Bunge, Hedysarum scoparium Fiseh.et Mey, Caragana korshinskii Kom and Calligonum mongolicum Turcz,the results as follow:1. Measuring branch angle and branch order with Strahler, he different psammophytes have dispancy in branch angle. Base on lessening the completive pessure and optimisve spatial using,the branch angle generaly increased from inside to outside. Holoxylom ammodendron Bunge, Hedysarum scoparium Fiseh.et Mey, Caragana korshinskii Kom have strong ability of branch ramification.The branch angle is70～85°.2. Cutting the plant from ground by the 20cm step high degree, measuring the biomass in 20cm and dividing into 6 classes accroding 2mm, 0～2mm,2～4mm,4～6mm,6～8mm,8～10mm and >10mm.The branch number and biomass of 6 classes are measured.(1) Holoxylom ammodendron Bunge, Hedysarum scoparium Fiseh.et Mey haven't significant difference of branch number in different indivadual plant and diameter on the same height; Caragana korshinskii Kom has significant difference of branch number in different diameter on the height 0～20cm,160～200cm; Calligonum mongolicum Turcz has significant difference of branch number in different diameter on the height 180～200cm.(2)The branch gross number of Holoxylom ammodendron Bunge is higher than the others.The branch gross number is above 1000 on the height 120～160cm; Hedysarum scoparium Fiseh.et Mey, Caragana korshinskii Kom and Calligonum mongolicum Turcz have the same variation tend of branch gross number; the general branch gross number of 4 psammophytes increaed with the height, and come to the maximum at the 0.5 times of tree height and then gradually decreased.(3)the branch number of Holoxylom ammodendron Bunge, Hedysarum scoparium Fiseh.et Mey, Caragana korshinskii Kom and Calligonum mongolicum Turcz in diameter 0～2mm,2～4mm,4～6mm,6～8mm,8～10mm increased with height,and then decreased; the brach number in diameter >10mm decreased with height.(4) The stepwise bifurcation ratio SBR5:6,SBR4:5,SBR3:4,SBR2:3,SBR1:2of Holoxylom ammodendron Bunge, Hedysarum scoparium Fiseh.et Mey, Caragana korshinskii Kom and Calligonum mongolicum Turcz showed the up-trend. Because of branch angle, the up-trend of different species in different height is different. With height increasing, the branch gross number and branch diameter gradually dereased, which affected by biomass spatial bearing capacity. And SBR5:6,SBR4:5,SBR3:4,SBR2:3,SBR1:2 are stable.(5)The biomass of 4 psammophytes decreased with height increasing.Because of spatial bearing capacity, the Hedysarum scoparium Fiseh.et Mey had largest biomass in 20cm and lowest down-trend,next is Caragana korshinskii Kom; Holoxylom ammodendron Bunge had less biomass but less down-trend than Hedysarum scoparium Fiseh.et Mey; Calligonum mongolicum Turcz and Hedysarum scoparium Fiseh.et Mey have the samilar biomass on 20cm.Having low branch angle and spatial capacity, the height of Calligonum mongolicum Turcz is 160～180cm and larger down-trend than Hedysarum scoparium Fiseh.et Mey.Branch biomass of 4 psammophytes which diameter >10mm decreased with height,the branch biomass of other class gradually increased with height.when come to the maximum,it began to decrease.(6)As far as the psammophytes concered, the water content ratio can indicate the anti-drought capacity. The Calligonum mongolicum Turcz had highest water content ratio(30.70%), which show its strong anti-drought capacity. The Holoxylom ammodendron Bunge and Hedysarum scoparium Fiseh.et Mey are the next 20%, Caragana korshinskii Kom had the lowest water content(15.42%).(7) The windward side width of 4 psammophytes Calligonum mongolicum Turcz,Holoxylom ammodendron Bunge,Caragana korshinskii Kom,Hedysarum scoparium Fiseh.et Mey respectively reach the maximum on 0.25～0.35;0.55～0.65;0.3～0.4;0.3～0.4 times of tree height. 3. Setting vane on the height 20cm;50cm;100cm;150cm,the wind break function can be measured through synchronously prognosticating controled plot and the place from which the distance are 1m ;2m ;3m on windward side. The results is follow:(1) 4 psammophytes have significant function of lowing wind speed which gradually reduced with distance increasing.With the different plant structure, on the height of largest branch number,the effect of wind break is obvious.Plant has little wind break effect on the top and base of plant.Comparing with earthbags naturaly formed by Nitaria sibirica Pall,it's more effective to reduce the wind speed and wind area than planted Holoxylom ammodendron Bunge,Hedysarum scoparium Fiseh.et Mey,Caragana korshinskii Kom,Calligonum mongolicum Turcz.(2) The wind break function has a correlation with barrier side and windward side width. There is a positive correlation between windward side width and barrier side width.Stumping bush did not affect the growth, but produce more branches.It increased barrier side and windward side width and function of lowing wind speed and area.The reuslt indicated that most of the sediment discharge (80%)ditributed in the height 0～10cm. The sediment discharge reduced in index law with height increasing. Stumping bush on the height 10cm is recommend.