Variation Characteristics Of Community Structure Of Different Vegetation Restoration Types In The Hilly And Gully Region Of The Loess Plateau

In this study,the fixed sample plots with different vegetation-restoration patterns were selected in the Fangta watershed and Zhifanggou watershed of Ansai County locted in the hilly-gully region of the Loess Plateau.The two Robinia pseudoacacia forests,two Caragana korshinskii forests,two Armeniaca sibirica & Robinia pseudoacacia forests and seven natural plant communities at different succession stages were selected to study the dynamic characteristics of species composition and community structure under different restoration patterns by year-by-year field investigation.The main results are as followling:(1)During the period of 30-35 years of vegetation restoration in Robinia pseudoacacia forest with felled,the community was in unstable state.The understory vegetation was always dominated by Compositae and Gramineae,the annual/biennia herb community has gradually evolved into perennial herb community,and the variation rate of species composition was high.During the period of 26-38 years of vegetation restoration in Robinia pseudoacacia forest with grazing,the community tended to be unstable from stable.The understory vegetation was always dominated by Compositae and Gramineae,and the most dominant position was competed by Compositae and Gramineae repeatedly.The perennial herb community was gradually invaded by annual/biennia herb,and the variation rate of species composition was high.(2)During the period of 20-38 years of vegetation restoration in Caragana korshinskii forest,the community was in stable state.The understory vegetation was always dominated by Compositae,Leguminosae,Gramineae,and Rosaceae.The understory plantation community had always been dominated by Artemisia gmelinii,accompanied by Patrinia heterophylla,Dendranthema indicum,Stipa bungeana,and Artemisia leucophylla and forming the community which was dominated by semi-shrubs and secondary by perennial herbs,and the variation rate of species composition was slow.(3)During the period of 8-21 years of vegetation restoration in the Armeniaca sibirica& Robinia pseudoacacia community,the community tended to be unstable from stable.The understory vegetation had been dominated by Compositae,Gramineae,Leguminosae and Rosaceae.The community was mainly composed of perennial herbs and sub-shrubs.The dominant species was competed by Artemisia gmelinii,Stipa bungeana,and Bothrichloa ischaemum after 18 years restoration,and the variation rate of species composition was fast.The forest density,canopy closure and average tree height showed an upward trend.(4)During the period of 40-45 years of restoration,the Artemisia gmelinii & Artemisia giraldii community was always dominated by Compositae,Leguminosae,Gramineae and Rosaceae,and Patrinia heterophylla and Artemisia gmelinii repeatedly competed for the status of dominant species,and the variation rate of species composition was slow.The Sophora davidii community was always dominated by Compositae,Leguminosae,Gramineae and Rosaceae,Artemisia gmelinii,Lespedeza davurica and Stipa grandis always occupy important positions,the community was in stable state,and the variation rate of species composition was slow.The Artemisia gmelinii & Stipa grandis community was dominated by Compositae,Leguminosae,and Gramineae and Artemisia gmelinii always in prime position and always maintain significant position,the community was in stable state,and the variation rate of species composition showed an upward trend.During the period 25-30 years of restoration in Artemisia gmelinii & Stipa bungeana community,Compositae,Gramineae,Leguminosae and Rosaceae always occupied the dominant position,Artemisia gmelinii had always maintained the dominant species status,and the variation rate of species composition was slow.(5)During the period of 10-15 years of natural restoration,Bothriochloa ischaemum community was always dominated by Compositae,Leguminosae,Gramineae,and Rosaceae.It was a community dominated by Bothriochloa ischaemum and accompanied by Lespedeza davurica and Artemisia gmelinii,the community was in stable state,and the variation rate of species composition was slow.The Stipa bungeana community was always dominated by Gramineae,Compositae,and Leguminosae,with a competitive advantage between Compositae and Gramineae.Artemisia gmelinii gradually replaced Stipa bungeana as the dominant species,and the variation rate of species composition had gradually increased.During the period of 5-10 years of restoration in Artemisia scoparia community,the vegetation is always dominated by Compositae,Leguminosae,Gramineae,Rosaceae,the status of the dominant species was not significant,the community was in unstable state,and the variation rate of species composition was rising.