| The vegetation restoration of erosion gullys is a difficult point in vegetation construction of soil and water conservation in the Loess Plateau.To explore the construction techniques of closed-to-nature vegetation in the erosion gullys,60 different forms of erosion gullys and Liugou small watershed closed for 35 years in Cai Jiachua watershed,which is located in Ji Country of Western Shanxi Province were investigated.The erosion gully morphological characteristics were extracted by using field measurement and GIS technology,and types of morphology were classified by using principal component-cluster analysis.Both of line transect and quadrat sampling methods were employed to survey the status vegetation in ditch,slope in erosion gully.The characteristics of plant communities in different erosion gullys were analyzed to evaluate the degree of coupling and coordination between gully morphology and their vegetation.The long-term dynamic changes of plant communities in the Liugou small watershed which closed for 15 years,26 years,and 35 years were analyzed by using the line transect sampling method and historical survey data.The results are as follows:(1)The 19 morphological indicators were selected to classify the erosion gullys into 6 types(Type ?,Type ?,Type ?,Type ?,Type ?),which were named:Micro-scale extremely narrow gully,Small-scale extremely narrow gully,Medium and small-scale narrow gully,Medium-scale narrow gully,Large and medium-scale wide gully,Large-scale extremely wide gully.Type ? and Type ? erosion gullys had smooth edge,regular shape,and narrow ditch width.Type ?,Type ?,Type ?,and Type ?erosion gullys were severely fragmented,irregularly shape,and gradually expanded toward the bank.12 indexes such as perimeter,catclunent area,vertical drop,average width,maximum width,and average width to depth ratio were the basic parameters that represent the shape of erosion gullys and could be used for the classification of erosion gullys.(2)The main morphological parameters of each type of erosion gully were as follows:The catchment area of type ? gully was 229?328 m2.and the average width was 1.3?7.9 m.The catchment area of type? gully was 780?4142 m2,and the average width was 7.1?14.1 m.The catchment area of the type ?gully was 5659?13927 m2,and the average width was 18.2?30.5 m.The catchment area of the type ?gully was 14333?29446 m2.and the average width was 25.8?37.4 m.The catchment area of type ?gully was 23672?54894 m2,and the average width was 49.9-67.0 m.The catchment area of type ?gully was 132386 m2,and the average width was 142 m.The perimeter,catchment area,average width,and maximum width of the erosion gullys from type ? to type ? showed an increasing trend,and the longitudinal gradient decreased gradually.The remaining parameters had no obvious changes.(3)The main vegetation characteristics of various types of erosion gullys were as follows:Type ?gully was mainly composed of the shrub xerophyte vegetation.Type 11 gully was mainly composed of drought-tolerant shrub mesophyte vegetation.Type III gully was mainly composed of the tree and shrub mesophyte vegetation in climax stage.Type IV gully and type V gully were both mainly composed of the shade loving tree and shrub mesophyte vegetation in climax stage.Type ? gully was mainly composed of the tree mesophyte vegetation.The species diversity of type ?-? erosion gully were respectively as 2.2459?2.9160,2.6674?3.7368,3.5875?4.1610,3.0762?4.1531,3.4755?4.2163 and 4.2039.Species richness were respectively as 6.0?9.2,9.0?15.1,16.3?24.5,14.0?23.5,17.4?23.6 and 29.0.They all showed increasing trends.(4)The coupling relationship showed that the maximum width,average width,perimeter and catchment area of erosion gullys had the greatest impact on the characteristics of vegetation.The right slope in type ? gully had the greatest impact on the characteristics of vegetation,the perimeter in type ?and type ? gully had the greatest impact on the characteristics of vegetation,and the left slope of type? and type IV had the greatest impact on the characteristics of vegetation.Type ?,type ?,type ?erosion gullys were weakly coordinated level.And type ?,type ? erosion gullys were moderately coordinated level.And the overall erosion gully morphology and plant community structure had reached a relatively stable and coordinated development relationship.(5)When the Liugou small watershed was closed for 15 years,26 years and 35 years,the coverage reached respectively 77.5%,89.1%and 93.6%.The annual growth rate of the overall coverage rate slowed down after 26 years of the closed watershed,and the small watershed had been formed forest vegetation when closed for 26 years.The small watershed had been basically closed and the habitat restoration had been better when closed for 35 years.(6)The improved rate of vegetation abundance in the closed small watershed in the period from 26 years closed to 35 years closed was slower than that of the period from 15 years closed to 26 years closed.The community similarity between the shade slope and semi-shady slope were increasing,and the rate of species replacement were slowing down.The same situation existed on the sunny slope and semi-sunny slope.As time prolongs,there was increased similarity between vegetation communities in the same habitat,and the structure of the communities gradually turned to be stable,even though they might still be the stage of progressive succession. |
PDF Full Text Request