| The development of gully erosion has seriously threatened the local ecological environment and social and economic development in the Dry-Hot Valley Region of Jinsha River.In order to find out the influence of vegetation restoration on headwater erosion in gully development area in the dry-hot valley of Jinsha River,gullies with different active degrees were selected in gully development area of Yuanmou.To explore the dominant species and community structure characteristics of gully head with different activity,this study used the method of field vegetation survey to record the plant species,quantity,coverage,height and other indicators in different areas,and calculate the similarity and diversity of plant communities.Meanwhile,physical and chemical properties of soil were measured.In addition,an in-situ scouring experiment was used to measure runoff velocity,depth and width,and the hydrodynamic factors were calculated,such as Reynolds number,Froude number,resistance coefficient,runoff shear stress and runoff energy consumption.This research would be helpful to find out the change of water dynamic characteristics of runoff in the process of headwater erosion under different vegetation restoration measures,and to evaluate scientifically the role of vegetation restoration in the process of gully headwater erosion.Our results showed that the number of plant species tended to increase with incr-easing the gully stability.28 species of plants,which belonged to 28 genera of 12 families,were found in the active gully.29 species of plants,which belonged to 29 genera and 16families,were found in the semi-stable gully.37 species of plants,which belonged to 15families and 35 genera,were discovered in the stable gully.According to the life types in those gullies,vegetation communities could be divided into three layers(i.e.,herb layer,shrub layer and tree layer)for different active levels of gullies.There was no tree layer in the active gullies.The dominant specie in the herb layer was Heteropogon contortus,and the second dominant species were Bothriochloa pertusa and Aristida adscensionis.The dominant specie in shrub layer was Dodonaea viscosa,and the second dominant specie was Leucaena leucocephala.The dominant specie of tree layer was Azadirachta Indica,and the second dominant specie was Eucalyptus robusta.As the gully stability increased,the coverage of each vegetation community enhanced.The plant communities of different active levels of gullies were dominated by perennial herbs and shrubs,as well as less few species of trees,in which the dominant species were the same and played similar roles in the plant communities.However,as stabilization of the gully increased,the quantity and diversity of trees gradually increased.For active gullies,semi-stable gullies and stable gullies,the plant community similarities were middle similar in the herb layer,extremely similar in the shrub layer,and extremely different in the tree layer,respectively.As the stability of gully changed,the tendency of convergent evolution obviously appeared in the shrub layer.However,no obvious tendency of convergent evolution were found for the herb layer and tree layer.Those results indicated that the activity of gully played an important role in the community function of herb and tree layer,while the community function of shrub layer was less affected by the activity of gully.Considering all the factors mentioned above,an obvious difference in the vegetation structure was observed during different activity levels of gully,and this result could provide scientific basis for gully ecological restoration in the further studies.Soil samples were taken from different spatial parts of gully(upstream catchment area,gully wall and gully bed)under different activity levels.Significant differences in the content of soil particle size fraction and organic matter content were found among gullies under different activity levels.The sand content was 50%higher than the content of clay and silt for each part of gullies.As the gully stability increased,the soil sand content gradually decreased,while the content of silt,clay,SOM and TN increased.Meanwhile,the soil rill erodibility(K_rvalue,s/m)of gully decreased with increasing the gully stability.K_rvalue in the active gully was higher than that in the semi-stable gullies and stable gullies.In addition,an obvious difference in soil critical shear force(τc,Pa)occurred in the different active gullies,while no obvious change tendency could be found.Significant differences in Kr values were found in the different parts of gully,and Kr values in the upstream catchment areas were higher than those in gully wall and gully bed.Among different hydrological conditions,Kr under seepage condition in different spatial parts of gully were higher than those under drainage and saturation condition.Gully activity(vegetation restoration condition),near-surface hydrological condition,soil particle size fraction and content of SOM could be obviously affected soil erodibility in the gully developed areas of Jinsha River Dry-hot Valley Regions.This experiment involved upstream catchment areas containing one-and two-year native grass(Heteropogon contortus)and bare land drained to bare gully headcuts,i.e.,G1,G2 and G3.In Gully 4,Heteropogon contortus and Agave sisalana were placed in the upstream catchment area and gully bed,respectively.In the drainage area,the runoff of the plots after planting vegetation(GJ1,GJ2 and GJ4)were in a slow-flow state(Fr<1),while runoff of the bare plot(GJ3)was in a rapids state(Fr>1).In the gully bed,the runoff of vegetated plot(GC4)was in a slow-flow state(Fr<1),while the runoff of bare plots(GC1,GC2 and GC3)were in a rapids state(Fr>1).This result showed that in this experimental state,after planting native vegetation,at different parts of the gully head,the runoff flow pattern changed from rapid flow to slow flow.As the flushing time continued,the flow shear stress increased first and then gradually tended to be stable in each experimental plots,but there were significant differences among different measures.Compared to the bare land,vegetation restoration significantly decreased the flow shear stress at different parts of gully.In terms of time,the Darcy–Weisbach friction factor(f)and flow energy consumption at different parts of the gully increased first and then gradually tended to be stable.Moreover,different vegetation restoration measures significantly improved the surface resistance coefficient and increase the flow energy consumption,thus reducing soil erosion.Compared with bare land,the experiments showed that planting native vegetation can effectively reduce the sediment content of runoff,which was shown as G3>G4>G1>G2.It could be seen that by increasing vegetation cover at the gully head,the surface resistance coefficient and the runoff energy consumption can be effectively increased.As a result,the runoff flow pattern can be changed from rapid flow to slow flow,the runoff shear force was reduced,and the sediment yield is correspondingly reduced,so as to effectively weaken the traceable erosion force of the gully and intercept the runoff and sediment. |
