Morphological And Structural Characteristic Of Tamarix Cones And Its Response To Climate Factors In Lop Nor Region

Because of the unique geographical location and fragile ecological environment,Lop Nor,Xinjiang has become the most representative arid zone in the world.It is also the most sensitive region for global climate change.The environmental evolution of Lop Nor region is a microcosm of the whole arid northwest region and even the world,and has become one of research hotspot.As a typical aeolian biological landscape type in arid and semi-arid desert areas,Tamarix cones can reflect the regional ecological environment status and changes better,and is of great significance to the monitoring and evaluation of desertification and the reconstruction of regional environmental evolution history.According to the field survey and the remote sensing technology of UAV,this paper researched Tamarix cones distribution pattern and morphology characteristics,and combined with the data from nearby national weather stations and automatic weather stations,analyzes the corresponding relationship between Tamarix cones morphological structures and climate environment factors.The results are shown as follows:(1)The vertical structure of Tamarix cones is composed of the upper Tamarix cone sedimentary lamina and the lower river-lake sedimentary layer.The sedimentary lamina was formed by the combination of the leaves of Tamarix ramosissima and wind-sandy sediments,while the fluvial-lacustrine sediments were formed by the reduction of the height of wind erosion or water erosion in the dry flood plain and lake terraces.The field observation section on the spots can find the obvious boundary between sedimentary layers and sediments of river and lake.Examples of such vertical structures can be found at the Kongquehe observation site and the east Milan observation site: the higher the height of sediments of the lower river and lake is,the worse or even dead top Tamarix thickets are.In the observation site of Hongliujing,the Tamarix cones have a large proportion of sedimentary layers and dense Tamarix ramosissima thickets,while the river-lake sediments are only found at the bottom of the Tamarix cones.(2)The observation sites of Tamarix cones are mainly distributed on river terraces and flood flats in Kongquehe observation site.The height of Tamarix cones is quite different,and the long axis of Tamarix cones is mostly close to east-southeast and northwest.The long axis has a slow slope,while the short axis has a steep slope.The observation sites of Tamarix cones in the east of Milan are distributed on the edge of the alluvial fan in front of the mountains.Here,Tamarix cones are mostly connected together to form larger dunes and longitudinal dunes.The height of the isolated Tamarix cones varies of several meters.The direction of the long axis of the Tamarix cones is close to that of the northeast and southwest.The long axis is generally longer,while the length of the short axis is obviously shorter.The combined sanddune beams are banded and the base shape of Tamarix cones is nearly round or oval.The observation sites of Hongliujing are distributed on the terrace of dry lake basin.The Tamarix cones here are generally lower in height but larger in volume.The long axis of Tamarix cones is northeast and west-southwest.The long axis of the Tamarix cones is slightly longer than the short axis,the contour lines around are relatively sparse,the slope is relatively slow,and the base shape of the Tamarix cones is approximately wedge or ellipse.There are significant linear correlation between the long axis and the short axis of the Tamarix cones at the three observation sites,indicating that the long axis and the short axis are in a coordinated growth relationship.Among the correlations between the height and the bottom area,it has a good correlation only at the Milan site,while the other two are not strong.(3)The average annual wind speed in Lop Nor region is relatively small,generally between 1.1 and 3.45 m/s.There is a significant seasonal difference in the monthly average wind speed of each station.The average wind speed is generally the largest from March to June,and the smallest from November to January.The wind direction distribution and frequency of the sand-driving wind in each station are as follows: Ruoqiang has the highest sand-raising wind frequency,and the sand-raising wind direction is mainly concentrated on the direction of partial NE and partial SW,followed by Luozhong.The sand-raising wind direction is mainly concentrated in the direction of partial W and partial E,and the last is Tieganlike,and the sand-raisingwind direction is mainly concentrated on the direction of partial E.The main sand-bearing wind direction and its frequency of the three weather stations in Tieganlike,Ruoqiang and Dunhuang can correspond well with the long axis strike of the Tamarix cones at each observation site,which means that the long axis of Tamarix cones at Kongquehe observation site is east-southeast and northwest tendency corresponding with the main sand-bearing wind direction of partial E and partial W.The northeast and southwest strike of the long axis of Tamarix cones in the east observation site of Milan corresponds with the main sand-bearing wind direction of NE and SE.The east-northeast and west-southwest strike of the long axis of Tamarix cones in the observation site of Hongliujing corresponds with the main sand-bearing wind direction of slant W and slant E.And sand-driving wind mainly in Spring and Summer,when the tamarix is in growth period,the sand sediment accumulation stage,but the two automatic weather stations are greatly influenced by surrounding landscape,as well as the used time is short,the actual observed data on wind speed and direction is not so actual,and the response is weak in the study area.The sand transport potential of each wind direction at each station,and the main sand transport potential and wind direction are close to the direction of Tamarix cones at each observation site.The annual sediment transport potential and synthetic sediment transport potential of each station can well reflect the sediment transport capacity of each station,and the synthetic sediment transport direction of each station is consistent with that of the corresponding observation points.(4)The vegetation coverage and erosion or accretion effect influence on Tamarix cones structure.In the areas with high coverage of Tamarix bushes,the wind-sand flow is blocked and deposited,forming Tamarix cones.The different shapes of Tamarix cones has been formed in their different developing stage.The erosion or accretion affect on the erosion position and morphology of the Tamarix cones.