The Study On Vegetation Restoration Model Of Highway Slope In Northwest Semiarid Region And Its Effect On Soil And Water Conservation

Located in the northwest border of China,Ili Valley suffers the problem of frequent water and soil loss in high deep slopes and areas with low vegetation coverage,which is characterized by the rapid desertification and difficulties in the vegetation restoration,due to its unreasonable land use.On purpose of promoting both highway construction and the harmonious development of the ecology,the study on vegetation restoration models of highway slope and its effect on soil and water conservation is of great significance.Based on the unique climate and ecological characteristics of Ili Valley,a comprehensive method was used in this study to investigate and analysis the plant resources of road area and their characteristics,and the grey correlation method was used to evaluate effects of the current vegetation restoration models of the highway slopes.On this basis,the effects of different vegetation restoration models on soil and water conservation were studied by analyzing the stability of plant community shown in the vegetation-soil coupling model constructed by redundancy analysis method through membership function method,and the quality of vegetation restoration was comprehensively analyzed so as to provide technical support for vegetation restoration on highway slope in Ili Valley.The results are as follows:(1)63 species of wild seed plants found in Ili prefecture,which belong to 58 genera and 25 families,are all angiosperms.The largest family is Compositae,which has 9 genera and 11 species.Among these plants,Xinjiang's endemic plants,which are mainly annual or perennial herbs,are relatively dominant,indicating that the road environment in Ili prefecture has a relatively unique and closed ecosystem.The area type of genera of road area wild seeds plants is mainly north temperate zone,with high diversity of floristic compositions.After first-round selection,there are 44 plants from 21 families with high observation value,and 20 plants from six families with good soil and water conservation function as well as fine ecological adaptability.(2)After implementation of different measures on highway slopes in Ili Prefecture,the moisture content of soil,from the upper part to the lower part of the slope,varied from 4.1%to 24.5%,articulating a significant differences;the soil bulk density did not have significant differences in the upper part of the slope(P>0.05),but indicated significant differences in the lower part of the slope(P<0.05);the average total soil porosity was between 30-50%,and there were no significant differences related to soil porosity on the upper slope(P>0.05).The highway slope with engineering protection and natural restoration measures showed better vegetation coverage,and the vegetation coverage of fill slope was significantly higher than that of cut slope(P<0.05).On excavation slopes,the highway slope with natural restoration measures shows better soil and water conservation effect;in the filling slopes,the soil and water conservation effect of the slope where measures of arched skeleton+sowing grass seeds were taken is better.The study area of highway slope is suitable for natural restoration supplemented by certain soil and water conservation measures,which is more conducive to slope ecological restoration.(3)Carrying out the experiments of vegetation restoration on the Nileke-Gongliu section of provincial highway S242,the results show that the vegetation coverage and plant density of the plot with Agropyron tenuifolia(10g/m~2)+Festuca arundinacea(5g/m~2)+Elymus(3g/m~2)+Medicago sativa(7g/m~2)+Sainfoin(3g/m~2)+Caragana korshinskii(6 plants/m~2)as vegetation restoration mode were 1.37 and 2.32 times higher,respectively,than that of the control groups;and under this combination,the soil structure,the anti-erodibility and the anti-scourability had also improved to a large extent.With the increase of soil thickness,the effect of plant on soil improvement was accelerated first and then slowed down.The coverage of vegetation,height and density of plants increased by 27.3%,62.0%and 45.5%,respectively,when the soil thickness increased from 5cm to 10cm,and the Simpson index as well as evenness index showed an increasing trend.With the continuing increase of soil thickness,the height of vegetation as well as the density of plants were tending towards stability,while the coverage of vegetation showed a slight growth tendency;the growth rate of the Simpson index and the evenness index was first fast then slowed down.When the soil thickness increased from 15cm to 20cm,the diversity index did not show a significant increase.Soil thickness of 10cm is the threshold to ensure the vegetation restoration effect of highway slope in Ili Valley.(4)The relational coefficient between soil factors and plant community diversity index was0.25?0.50,with medium correlation and strong correlation being the main ones,among which the Margalef index was the most influenced.Among all the soil factors,soil porosity and soil anti-scourability have the biggest average correlation coefficient of 0.43,which is 48.27%higher than that of minimum non-capillary porosity(0.29),articulating that soil porosity with the soil anti-scourability have the biggest impact on the quality of vegetation restoration,while the non-capillary porosity may be the main contributing factor which results in the differences btw effects of vegetation restoration.In this area,soil thickness is the key factor affecting the effect of highway slope in preparation and restoration.Increasing the thickness of overlying soil to some extent could accelerate the coupling process between plant and soil,thus improving the plant community stability.In order to ensure the results of vegetation restoration on highway slopes in this area,it is suggested that the backfill thickness of the surface soil on the slope should be more than 15 cm.