The Restoration Characteristics Of Degraded Seriphidium Transiliense Desert Grassland Under Fenced Condition Based On HJ-HSI

Fencing is a common way used to repair the degraded grassland.And it is the basis for managing fenced grassland scientifically to getting the restoration characteristics timely.In this study,we selected the Seriphidium transiliense desert grassland as the study object.The community characteristics of the fenced and unfenced grassland(N:fenced area,W1:unfenced and heavy-degraded area,W2:unfenced and middle-degraded area)were studied,from the three aspects of vegetation community,ground spectral and HJ-HSI spectral data,and from the three seasons of spring,summer and autumn.The purpose is to clarify the recovery characteristics of such grassland and improve the accuracy on monitoring fenced grassland community by using HJ-HSI spectral data.The main results were as follows:(1)Fencing promoted the restoration of grassland community characteristics,and community height,coverage and aboveground biomass showed an increasing trend,but the community density was expressed as W1>N>W2;The species diversity increases and tends to be evenness.Petrosimonia sibirica is in the dominant position in unfenced and middle-degraded area(W2),but the dominant species is S.transiliense both in unfenced and heavy-degraded area(W1)and fenced area;fencing promoted the restoration of S.transiliense,which is also characterized by the fact that the fenced is superior to the unfenced.From spring to the autumn,all the indexes were increase in both fenced and unfenced plot.(2)The ground spectral reflectance of dominant species in fenced area was lower than that of the unfenced plot,which followed in spring:P.sibirica of W1>S.transiliense of W2>S.transiliense of N;but no obvious change rule in summer;S.transiliense of W2>P.sibirica of W1>S.transiliense of N in autumn.The ground spectral reflectance of the grassland community were W1>W2>N in spring and autumn,and N>W2>W1 in summer.Not only dominant species but also grassland community had the highest ground spectral reflectance in autumn,and had the redshift in different degrees.These also indicated that the vegetation in the fenced area were superior to the unfenced area.Furthermore,in spring,the ground spectral variables and band variables were correlated with grassland coverage and aboveground biomass highly,and the coefficient of determination was more than 0.5,and the accuracy was more than80%.(3)The spectral reflectance of HJ-HSI was different with that of ground community in different seasons,followed with the reflectance of W2 was the highest,N>W1 in band 500~700 nm and W1>N in band 700~870 nm in spring;the reflectance of N was the lowest,and W2>W1 in 500~720 nm,but W1>W2 in 720~870 nm in summer;W1>W2>N in autumn.The rededge position of the spectral of the fenced area was redshifted,indicating that the vegetation in the fenced area is superior to the unfenced area.The suitable season was also in spring on using the HJ-HSI spectral to estimate the grassland coverage and aboveground biomass.The accuracy is improved by using the ground spectral to correct the estimation model with lower coefficient of determination.In spring,the best accuracy of the coverage predictive model was 85% or more:N was constructed by normalized index in band 669.21 nm and 765.11 nm,y=4730.2x~2+183.11x+24.735;W1 was constructed with DVI,y=9.955x~2-58.712x+129.3,and W2 was constructed by R_n,y=3.8826x-48.97.The best accuracy of the aboveground biomass estimation model was above 75%:N was constructed by DVI,y=42.805x~2-77.061x+120.64,W1 was constructed by R_n,y=0.6618x~2-30.871x+386.25,W2 was constructed by normalized index in band 652.09 nm and 732.01 nm,y=2206.9x+28.313.