Effect Of Vegetation Restoration On Soil Property And Soil Erodibility Of Gully Heads In Different Vegetation Zones Loess Tableland

Since the project of “grain for green” was put into practice in the loess-tableland,vegetation construction in the Loess Plateau has achieved remarkable results.During this process,the plant community types and vegetation coverage have increased significantly,while the positive effect of plant roots on soil structure has been enhanced,and soil properties and soil stability have been improved.In this way,the soil resistance of gully heads has been improved obviously,and the occurrence of gully headward erosion has been well controlled.The vegetation distribution in the loess tableland affected by climate(e.g.rainfall)is obvious.The effect of vegetation restoration on soil erodibility of gully head in different vegetation zones in the loess tableland is significantly different.Thus,this study took the gully heads with natural restored vegetation as the research target,and three Loess-tableland regions including Luochuan Tableland(the forest zone,recovery period3?32 years),Dongzhi Tableland(the forest-steppe zone,recovery period 3?30 years)and Baicao Tableland(the steppe zone,recovery period 2?22 years)were selected.The study investigated plant community characteristics and root characteristics of different restoration ages at gully heads,and explored the changes in soil properties along 0?70 cm soil layer with the farmland as the control.As a result,this research clarified the effects of vegetation restoration on soil erodibility of gully heads in different vegetation zones,determined the factors affecting soil erodibility of gully heads,and deepened the understanding of the effects of vegetation restoration on soil erosion in the loess-tableland.The results can provide a scientific basis for controlling gully for protecting the loess-tableland and determining the optimal vegetation restoration pattern in the loess-tableland.The main conclusions were as follows:(1)The characteristics of plant community in vegetation restoration process on gully head were explored.With the natural restoration succession on gully heads,biomass of plant communities in these three vegetation zones was higher in the early stages of the succession,with a decrease in the middle,and then gradually increased.Patrick richness index of gully heads in Luochuan Tableland and Dongzhi Tableland was relatively small at the initial stage of recovery,and then showed an increasing trend with the increase of restoration years.With the increase of recovery years,Simpson dominance index of the three areas gradually decreased,and Shannon-wiener diversity index and Pielou evenness index showed an increasing trend.(2)The characteristics of root system during vegetation restoration process on gully head were clear.With the increase of vegetation restoration ages of gully heads in the three vegetation zones,root biomass,root length density,root surface area density and specific root length gradually increased.And with the increase of soil layer depth,the above four parameters showed a trend of decreasing.(3)Clarified the effect of vegetation restoration on the soil properties of the gully.With the increase of restoration years,in the forest zone,soil bulk density of gully heads increased first and then decreased,and soil porosity showed a trend of decreasing first and then increasing.In the forest-steppe zone,soil bulk density of gully heads gradually decreased and.soil porosity gradually increased.And in the steppe zone,soil bulk density increased first and then decreased,and soil porosity decreased first and then increased.Soil organic matter,water-stable aggregate content,mean weight diameter of aggregate,and saturated hydraulic conductivity of the three vegetation zones all increased gradually.(4)The impact of vegetation restoration on soil erodibility of gully head was clarified.The comprehensive evaluation indexes of soil erodibility of gully heads in forest zone,forest-steppe zone,and steppe zone decreased significantly with the increase of recovery year(P<0.05).The soil erodibility degree of gully head was “high” in farmland and early restoration period sites.As the vegetation restoration progressed,the medium-term restoration period sites grade was “higher” and the later restoration stage was “medium”.Vegetation restoration significantly reduced soil erodibility of 0?10 cm soil layer of gully head,but had less effect on 55?70 cm soil layer.(5)Clarified the correlation relationship between soil properties,soil erodibility and vegetation restoration of gully heads.Soil properties of gully heads in the three vegetation zones were closely related to biomass of plant communities,Simpson dominance index,Shannon-wiener diversity index,root biomass,root length density,root surface area density,and specific root length.Soil erodibility was significantly correlated with other vegetation diversity characteristic indexes and root characteristic indexes.