Resilience Of Vegetation And Soil On Abandoned Slope In The Hill-Gully Loess Plateau

Resilience of vegetation and soil is an important indicator for evaluating sustainable development of degraded ecosystem of abandoned slope in the hill-gully Loess Plateau region.It can provide a scientific basis for management of the degraded ecosystem and the decision-making of soil and water conservation.Therefore,we took Ansai county as study area and abandoned slope as our research target.Combined cannikin Law,field investigation and indoor analysis,and literature data and measured data analysis were used.Characteristics of vegetation and soil were analyzed on abandoned slopes.Measuring method of resilience of vegetation and soil was established on abandoned slope,and on this basis,resilience of vegetation and soil on abandoned slope was evaluated and then,we explored limiting factors on development of resilience driven by vegetation regeneration on abandoned slope.The main results as follows:1.Vegetation(or undergrowth vegetation)types were mainly Bothriochloa ischaemum and Artemisia gmelinii communities on natural abandoned slope and Prunus sibirica+Robinia pseudoacacia plantation that abandoned in 1999,and they were in the middle or late successional stage of community succession.Undergrowth vegetation types were mainly Setaria viridis,Stipa bungeana,Aneurolepidium dasystachys,Patrinia scabiosaefolia and Cleistogenes squarrosa communities which were in the early or middle successional stage on Robinia pseudoacacia plantation that abandoned in 1999,and the undergrowth vegetation restoration was limited in comparison with the vegetation on natural abandoned slope.Undergrowth vegetation types were Solanum septemlobum and Artemisia gmelinii communities on Robinia pseudoacacia plantation and Caragana korshinskii plantation abandoned in 1982,and the vegetation features had significant differences between them.Coverage of undergrowth vegetation recovered,significantly,on Robinia pseudoacacia plantation that abandoned in 1982 in comparison with that in 1999.Undergrowth vegetation community was from early to middle or late successional stage on Prunus sibirica+Robinia pseudoacacia plantation in 8-17 years of abandonment.Canopy density was 0.40-0.67 on Robinia pseudoacacia plantation,and undergrowth vegetation community was from Stipa bungeana to Solanum septemlobum community in 25-34 years of abandonment.It indicated that the successional direction had changed.Canopy density was 0.40-0.65 on Caragana korshinskii plantation,and undergrowth vegetation was stable Artemisia gmelinii community in 25-34 years of abandonment.2.The conditions of soil nutrient,soil aggregate and soil water had differences in various degree among natural abandoned slope,Robinia pseudoacacia plantation and Prunus sibirica+Robinia pseudoacacia plantation that abandoned in 1999.It was useful for recovery of soil aggregate that slope was abandoned,naturally.There was a soil dry layer on plantation.There were no significant differences in soil bulk density,soil aggregate and soil nutrient between Robinia pseudoacacia plantation and Caragana korshinskii plantation abandoend in1982.Soil aggregate and soil nutrient recovered,significantly,on Robinia pseudoacacia plantation that abandoned in 1982 in comparison with that in 1999.Through ten years of restoration,soil nutrient recovered,significantly,but soil desiccation was not lessened on Prunus sibirica+Robinia pseudoacacia plantation,Robinia pseudoacacia plantation and Caragana korshinskii plantation.3.Resilience of vegetation and soil on abandoned slope could be evaluated in terms of 5aspects including process of vegetation succession,soil erosion control of vegetation,soil structural stability,soil nutrient supplying capacity and soil water supplying capacity.Degree of succession,coverage,soil organic matter content,soil water stable aggregate and soil water content in deep soil layer were selected as surrogates in the above 5 aspects,respectively.The positions of minimum and maximum thresholds of degree of succession,coverage,soil organic matter content and soil water stable aggregate were in initial and final states,respectively.Under the condition of undegraded soil water supplying capacity,minimum and maximum thresholds of soil water content in deep soil layer were steady water holding capacity and water holding capacity.4.Resilience index of process of vegetation succession was 0.00-0.11 on abandoned slope.Resilience indexes of soil erosion control of vegetation and soil structural stability was0.26-0.65 and 0.24-0.72 on abandoned slopes,and the resilience was stronger than that of process of vegetation succession.Some slope had been nearing steady state in the two aspects.Resilience indexes of soil nutrient supplying capacity were-0.02-0.01 and 0.37-0.40 on slopes abandoned in 1999 and 1982,respectively.The resilience was weak on slopes abandoned in1999,and,although the resilience was stronger on slope abandoned in 1982 than that in 1999,it also took a long time to reach steady state.Resilience index of soil water supplying capacity was 0.45 on natural abandoned slope abandoned in 1999,and it was-0.89--0.42 on plantations that abandoned in 1999 and 1982.It indicated that soil water supplying capacity was degraded on plantation.As time went by,the letdowns of development of resilience would change.For now,resilience controlled by process of vegetation succession and soil nutrient supplying capacity on natural abandoned slope abandoned in 1999.Resilience controlled by process of vegetation succession,soil nutrient supplying capacity and soil water supplying capacity on Robinia pseudoacacia plantation and Prunus sibirica+Robinia pseudoacacia plantation abandoend in 1999.Resilience controlled by process of vegetation succession and soil water supplying capacity on Robinia pseudoacacia plantation and Caragana korshinskii plantation abandoned in 1982.5.Initial soil seed bank density was 4832 seed/m~2 on natural abandoned slope abandoned in 1999.Seed density was 10186 seed/m~2 that inputed the slope through seed rain in 2 years and then total seed bank could up to 15018 seed/m~2.Seed density of shrub was only 11seed/m~2 in the total seed bank.Compared with the initial soil seed bank density,final soil seed bank density increased to 6997 seed/m~2,significantly,after 2 years.It indicated that seeds were accumulating in soil seed bank and seed resource was not limited in quantitative terms.However,seeds from trees and shrubs were scarce.Density of seed germination was 938seedling/m~2 during 2 years.Seedlings of different species that belonged to all the successional stages were represented.Rate of standing vegetation density to seedling density was only7.5%.It suggested that most seedlings could not establishment,successfully.There was a significant positive correlation between content and coverage of litter and soil nutrition content.Content and coverage of litter were less on herb community than that on shrub community.Thus,from the point of view of vegetation regeneration which driving ecosystem restoration,the letdowns,process of vegetation succession and soil nutrient supplying capacity,were limited by seed resource of trees and shrubs,seedling establishment and input of litter at present on natural abandoned slope abandoned in 1999.