Study On Relationship Of Sand-fixating Vegetation Pattern And Hydrological Process In Gurbantonggut Desert

Gurbantonggut desert is a typical sensitive area for climate change.The change Variation of Sand-fixating vegetation pattern and response to climate change has become a research role hotspot of modern ecology and hydrology.Based on landscape pattern-process theory,using the methods of belt-transects investigation,remote sensing inversion and model simulation,we studied dynamic characteristics of sand-fixating vegetation patterns and regional differentiation rule,analyzed the interaction relationship and key control factors between sand-fixating vegetation patterns and Hydrological elements,preliminarily clarified the feedback mechanism between sand-fixating vegetation pattern and hydrological processes.Research conclusions can provide the basis for artificial sand fixating vegetation construction and ecological management.The main conclusions are as follows.?1?Sand-fixating vegetation pattern showed obvious regional differentiation in southern Gurbantonggut desert.From the southern edge to the center of desert,the area of sand fixation vegetation patch is is reduced from 37.59 m² to 7.6 m²,but the density and fragmentation degree of vegetation patches is increasing and the shapes of vegetation patch tend to be simple.Most sand fixation vegetations are distributed in the interdune land of the fixed dunes and semi-fixed dunes,and on the slope and top of the mobile dune.During the periods of 1977—2010,sandy vegetation showed a?restoration-degradation-restoration?trend in southern Gurbantunggut desert,and the general trend was positive succession.Fragmentation of different sandy vegetation coverage showed different patterns,with increased fragmentation in relatively high coverage of vegetation and decreased fragmentation in relatively low degree of coverage of vegetation..?2?Precipitation is increasing,and precipitation pulse caused the migration of soil moisture between shallow and deep layers,and then had a positive effect on the evolution of sand-fixing vegetation pattern.During the past 55 years,precipitation is increasing(8 mm 10a^-1),and the precipitation of(5-10]mm and(10-15]mm increased by 3 mm 10a^-1,accounting for 75%of the total increased precipitation in southern of the Gurbantunggut desert.Precipitation pulse changes caused soil moisture is higher in spring than in summer.In spring the shallow soil moisture?0⁴0 cm?is higher than that of deep soil moisture?40¹00cm?,but in summer deep soil moisture?40¹00 cm?is higher than the shallow water?0⁴0 cm?.Soil moisture and temporal and spatial heterogeneity intensified sand-fixating vegetation pattern evolution..Migration of soil moisture promote or inhibit the growth of shallow root or deep root vegetation and influence the evolution processes of sand fixing vegetation community.The large precipitation events,which have the significant effects on deep root vegetation,such as shrubs?r=0.439⁰.476,P=0.085⁰.116?.Precipitation in the spring have significant effects on shallow root herbaceous vegetation?r=0.367⁰.612,P=0.05⁰.196?.With the increasing of soil moisture,the size-frequency distribution of sand fixing vegetation patches is shifted from the narrow-truncated power function to the wide-truncated power function,and the number of large sand fixation patch reduced,the average area increased,and the dominance of medium and high coverage vegetation and their connectivity are enhanced.Sand fixation vegetation could adapt to different soil moisture by the strategy of adjusting patch size.?3?There is a obvious positive feedback mechanism between sand-fixating vegetation pattern and soil moisture in southern Gurbantonggut desert.The increase of soil water content caused the increase of stomatal conductance and photosynthetic rate of sand fixation vegetation,which promoted the increase of vegetation vegetation NPP.Effects of soil moisture on sand-fixating vegetation is a"pulse-store"mode.the soil moisture above 40 cm depth is more sensitive to precipitation.When the daily precipitation is greater than 10 mm,it could influence the soil moisture of 40¹00 cm depth.When the precipitation was between5 mm and 10 mm,it could influence soil moisture of 0⁴0 cm depth.Increased soil moisture caused the stomatal conductance increased from 0.036 mol/m² S to 0.082 mol/m² S,and the photosynthetic rate increased from 0.12?mol/m² S to 12.98?mol/m² S.The increase of fixing vegetation pattern NPP increased the soil moisture in the root zone by inhibiting the evaporation of soil moisture under the crown,resulting in higher soil moisture for canopied than interspace.Water use efficiency is higher in sand fixation vegetation with coverage,and is lower in sand fixation with coverage.The feedback is stronger with higher soil moisture and vegetation coverage,and vice versa.The intensity of the feedback had a significant spatial heterogeneity.There was a downward trend along the longitude direction from south to north,and was decreasing trend along the latitude direction from the zone of E 87.5°-E88°to east and to west.