| The strong earthquake triggered numerous landslides and destroyed the original hydrology,vegetation,soil and other natural conditions.Research on the ecological and hydrological evolution of these landslides after earthquakes,the vegetation restoration and their mutual relationship have important theoretical and practical significance for the enhancement of water and soil conservation ability of the landslide,the steady improvement of eco-hydrological functions,as well as the self-recovery,self-regeneration and management of plant communities.However,the existing research rarely has a field investigation of the landslide body after the earthquake,and it lacks long-term follow-up research.To this end,this paper analyzes the various zones in the field of the Xiejiadian-Landslide caused by the 2008“5?12”Wenchuan Strong Earthquake,by setting the altitude gradient ecological sample zone and continuously(2009-2017)field observation.The hydrological-vegetation restoration of the landslide body has been studied year-by-year,and the main research contents and results are as follows.1.During the study period,as the vegetation of the landslide became more and more closed after the earthquake,the ecosystem experienced three stages,namely the herb community(Phase I)from 2008 to 2010,and the shrub-herb community in2010-2014(Phase II),and the increasingly complex structure of the tree-shrub-herbal community(Phase III)after 2014,the system's ecological hydrological indicators are developing well,as follows:the canopy rainwater penetration rate from Phase I(79.60%)>Phase II(77.80%)>Phase III(71.75%)is significantly reduced,litter interception efficiency increases rapidly,increasing from 8.79%(Phase I),20.66%(Phase II)to 38.05%(Phase III);In the undergrowth,the soil bulk density gradually decreased in three stages,and the soil porosity increased continuously.The soil saturated water content and field capacity were respectively 37.70%,10.21%of Phase I rose to 44.82%and 16.47%of Phase III,the capillary water capacity increased from about 22.00%in Phase I and II to 28.52%in Phase III,and the soil moisture continued to increase(in three stages For 66.81%,79.80%and 89.31%respectively).The surface runoff is significantly reduced with three phases,and the measured values are 30.58 mm,26.24 mm and 18.91 mm,with the same precipitation intensity(rain intensity 25 mm/h,rainfall duration 2 h).2.At the end of the study period(2017),the difference between the natural evolution characteristics of the hydrological indicators of the landslide ecosystem in the elevation gradient is:the canopy rainwater penetration rate increases with the elevation,and it is below the lower slope(samples 1~3),middle(samples 4~6),and upper(samples 7~9)were 71.34%,78.1%,and 79.66%,respectively;litter interception and interception efficiency is diminished with the elevation,and the difference in natural water content between the bands is small(45.20%-51.20%,average 47.71%).In the undergrowth,soil bulk density increases with altitude(1.17g/cm~3-1.33 g/cm~3);Soil total porosity,saturated water content,capillary water capacity,field capacity and soil moisture are all reduced along with elevation.The soil moisture is 89.66%,85.86%and 72.13%,respectively,in the lower,middle and upper parts of the slope.The initial runoff rainfall on the slope decreased slowly with increasing altitude(from 6.80 mm to 5.13 mm);at the same precipitation intensity(rain intensity 25 mm/h,rainfall duration 2 h),the surface runoff increased with altitude,and the value is 17.51 mm-19.32 mm in the lower part,and the value is 19.89mm-26.18 mm in the middle part,and the value is 26.44 mm-30.86 mm in the upper parts of the slope.3.During the study period,the inter-annual variation of plant species composition of landslide body was obvious,showing a significant increase in diversity.In 2009,the number of plants,genus and species were only 20,35 and 53 respectively.By2017,the distribution reached 54 families,66 genera,and 84 species.Among them,the 84 plants in the end of the study which included the number of trees,shrubs,herbaceous plants was 12,12 and 60 species respectively,of which up to 25 species have become the dominant plant of the community,and Alnus cremastogyne and Rhus chinensis Mill,Rubus tephrodes Hance and Spiraea salicifolia L.,and Equisetum hyemale L.and Selaginella nipponica were respectively the dominant species of the arbor,shrub and herb layers.In the period(2009-2017),it showed an increasing trend which includes the plant Shannon-Weiner index,Pielou Evenness index,Simpson Diversity index and Margalef Richness index.4.At the end of the study in 2017,the natural evolution characteristics of vegetation ecological indexes in the landslide system showed differences with the elevation gradient.The plant Shannon-Weiner index,Pielou Evenness index and Simpson Diversity index gradually decreased with the altitude increasing.The Margalef Richness index increased gradually.The biomass of fresh and dry weight of herbaceous plants increased rapidly,and the water content of herbaceous plants tended to be stable after increasing rapidly,and the water content reached the maximum value is 66.49%at 1350 m Altitude,and the minmum value is 53.93%at1390 m Altitude.The total interspecific correlation of 25 dominant species in the landslide system showed positive correlation,and could be divided into 4 ecological species groups.Among them,the Group I was dominated by Arbor,including 13species of which includes Betulaceae,Lauraceae,Anacardiacea,Vitaceae.etc.Most of them are constructive species and dominant species,which have a significant correlation with each other,and have an important effect on community succession,structural stability and vegetation restoration.5.The correlation analysis showed that the canopy penetration rate(PR)of the community was significantly correlated with the fresh weight(WB),dry weight biomass(DB)and the similarity dominant species of adjacent samples(SA).The formula is:PR=60.689+16.099WB+22.884DB-0.092SA(R~2=0.837).The water content of litter(LW),and soil moisture content(including saturated water content(SC),capillary water holding capacity(CH),field capacity(FC),and soil moisture(SM))of the community have a significant negative correlation with the WB and DB,and have a significantly positively correlated with SA:LW=55.080-7.775WB-10.433DB+0.04SA(R~2=0.809),SC=60.395-14.483WB-19.035DB+0.156SA(R~2=0.776),CH=50.481-25.941WB-40.189DB+0.221SA(R~2=0.801),FC=0.704-0.813WB-1.318DB+0.101SA(R~2=0.861)and SM=114.479-20.666WB-12.418DB+0.175SA(R~2=0.981).The initial runoff rainfall(IR)and surface runoff(SR)of the slope were significantly correlated with plant fresh weight and dry weight biomass and the similarity dominant species of adjacent samples:IR=1 0.9 6 8-3.8 1 8 W B-5.1 3 2 D B+0.0 4 6 S A(R~2=0.9 3 2),S R=1 4.7 9 2+1 0.6 2 7 W B+1 0.2 8 4 D B-0.0 0 9 S A(R~2=0.8 7 5).The result of this paper showed that the hydrological and vegetation of the Xiejiadian-Landslide have positive succession after the earthquake,and the ecosystem can be restored itself,and its evolution direction is progress succession.The results of this paper also have positively promoted the soil and water conservation,and the steady improvement of hydrological,and ecological functions of the landslide body caused by strong earthquakes. |
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