Research On Ecosystem Stability Of Liangucheng National Nature Reserve In Minqin,China

Mostly located in arid,semi-arid or even semi-humid climate zones,arid desert areas are characterized by strong sensitivity and poor stability,most of which in northwest China have natural reserves so as to protect the fragile local ecosystem and animal and plant resources.With very important ecological locations,arid desert reserves are distributed majorly on the edge of oases and desert transition zones.However,the ecosystem of reserves is faced with a number of problems like the gradual simplification of ecosystem structure and the decline of self-regulation ability and resistance to succession in addition to wind-sand erosion and desertification because of drought stress and human development and construction activities.Therefore,monitoring and evaluating the ecosystem of reserves have become an important content of regional ecological protection,which is realistic and urgent.As an important feature determining the rise and fall of an ecosystem,stability is one of the important indicators for measuring changes in the ecosystem.Research on ecosystem stability faces a lot of difficulties due to the non-linear relationship between the components of an ecosystem,the fluctuation characteristics of the system state,and the spatial-temporal heterogeneity of the system.At present,the definition and identification methods of ecosystem stability are still at the stage of extensive discussion,and a unified standard has not yet been formed.Research on the changes in the ecosystem stability of Liangucheng Nature Reserve can enrich the evaluation methods of ecosystem stability and provide a scientific basis for the ecological management and construction of reserves.Based on the connotation of ecosystem stability(resistance and resilience stability),Liangucheng Nature Reserve was taken as the research object,and the indications of some key structural indicators(ecosystem pattern and spatial heterogeneity)and functional indicators(like net primary productivity(NPP))and their impact on the ecosystem stability of the reserve were identified by using the positive and negative transformation index(PNTI)model,the dynamic analysis of landscape pattern as well as dimidiate pixel and Carnegie-Ames-Stanford Approach(CASA)models.The results are as follows:(1)From 1995 to 2017,the desert ecosystem was the main type of ecosystem in the reserve and accounted for more than 70%of the total area,followed by the shrub ecosystem occupying more than 10%of the total area.The ecosystem type of each functional partition was basically the same as that of the whole reserve.Due to the single type of ecosystem,the reserve was disturbed easily and changed.(2)From 1995 to 2017,the ecosystem pattern of the reserve developed in a favorable direction.From 1995 to 2000,the area which transferred from shrub ecosystems to desert and farmland ecosystems were 40,044.47hm~2,accounting for53.46%of the area which ransferred from the whole reserve.The positive conversion rate of the ecosystem was lower than its reverse conversion rate,indicating the change of the ecosystem in an unfavorable direction.From 2000 to 2017,the area converting from desert to shrub ecosystem in the reserve increased from 36,507.35hm~2 to48,934.47hm~2,suggesting that the reserve developed in a healthy direction on the whole.(3)The resistance stability of the reserve weakened first and then increased.From 1995 to 2000,the spatial heterogeneity of the ecosystem in the reserve increased due to the increased interference intensity of human activities,but the overall ecosystem of the reserve was reversely converted,accompanied by the degradation of the ecosystem and the decrease of resistance stability.From 2000 to 2017,the conversion trend of the ecosystem in the reserve was mainly positive with increased diversity and resistance stability due to the construction of the reserve and the implementation of a comprehensive treatment project in Shiyang River Basin.(4)The changing trends of vegetation coverage and NPP were not consistent.Vegetation coverage of the reserve declined first and then increased,reflecting that the resilience stability weakened first and then increased.The NPP of vegetation showed a trend of rising first and then falling twice,reflecting the fluctuation of resilience stability.(5)A non-linear relationship was found between the resistance and resilience stability of the reserve whose overall stability is not their simple superposition.Therefore,corresponding key indicators cannot be accumulated to indicate the overall stability and change of the ecosystem in the reserve,but explained its change mechanism from different sides.