| Degradation of vegetation in underground mines after ground deformation has attracted increasing concerns,however,there are still disagreements regarding the longterm effects of ground deformation on vegetation.A clear understanding in the mechanism of this phenomenon will benefit to a comprehensive decision-making between technical reclamation and natural restoration in mining area,which could reduce the cost of restoration and increase ecological resilience.Thus,it is extremely necessary to ascertain long-term effects on vegetation after mining activities,so as to provide a theoretical guidance for vegetation reconstruction in mining areas.To address these,Yungang mine,Datong City,Shanxi Province,was selected study area.Firstly,the basic data of ground deformation and vegetation were obtained by data collection,field survey and remote sensing.After that,logical reasoning and dynamic system modeling were applied to reveal the meachnism of long-term effects of ground deformation on vegetation.Then,mathematical modeling was used to construct the model and variables for evaluating long-term effects of ground deformation on vegetation.At last,a model for simulating long-term effects of ground deformation on vegetation was developed through system simulation methods.The aim of this dissertation is to demonstrate long-term effects of ground deformation on vegetation in semi-arid mines,and the objectives include revealing the mechanism of long-term effects of ground deformation on vegetation,and constructing models for evaluating and simulating long-term effects of ground deformation on vegetation,respectively.The main conclusions of this dissertation are listed as follows:(1)Ground deformation has long-term effects on vegetation,while the degree of effects is depended on the level of ground deformation.Ground deformation has both dynamic and static characteristics,which have short-term and long-term effects on vegetation respectively.When the surface deformation is static,it has the characteristics of spatial difference and state stability.According to the scale of influence on vegetation,ground deformation is divided into surface deformation that leads to overall vegetation change and local vegetation change,which are represented by ground subsidence and ground cracks,respectively.Correlation analysis results show significant correlation between vegetation structure parameters and topographic factors,as well as the degree of soil degradation and crack characteristics,showing that the change in terrain will lead to long-terms effects on vegetation.The severity of ground deformation is the key to the degree of effects on vegetation.The depth,angle and direction of subsidence are the key factors affecting vegetation by ground subsidence,which determine the site conditions of the vegetation;the cracking distance and the angle of subsidence are are the key factors affecting vegetation by ground cracks and determine the degree of soil degradation.(2)The long-term effects of ground deformation on vegetation is resulted from the degradation of vegetation and soil when ground deformation occurred,which limited the growth and succession of plant after ground deformation.According to the analysis of the process ground deformation affecting vegetation via the developed VegetationSoil-Weather Molde(VSW Model),when the ground deformation occurs,the substrate conditions of the vegetation and its soil are degraded,and the change of the substrate conditions will lastly limit the growth and succession of plant drivied by natural process in the long run.The intensity of the long-term effects is determined by the severity of the ground deformation,while relevant to the duration,climatic conditions,the substrate conditions of the vegetation and soil before the deformation,and the natural change coefficient of the vegetation and soil.The long-term effects of ground deformation on vegetation has spatial heterogeneity,temperal persistence,passivity and predestination.The results of long-term effects can mainly divide into two categories:changes in the state and type of vegetation,which come from the effects on growth status and community succession.(3)The long-term effects of ground deformation leads to the decline of the growth state of vegetation,while herb vegetation is most affected by ground deformation,followed by tree vegetation,and shrub vegetation.Based on constructed vegetation growth contrast model and growth process indicators,the trees,shrubs and herbs in the subsided area of study area are evaluated by comparing with the vegetation in natural contrast area.Rusults show that that the ground deformation in Yungang mine caused a decline of 6.79%,4.03%,and 15.10% in the growth status of trees,shrubs,and herbs from 1987 to 2017,respectively,compared with the vegetation in the natural contrast area.Among them,the indicators of trees and herbs declined to varying degrees,while the growth trend and normalized spectrum entropy of shrubs increased by 17.26% and2.77%,but the annual minimum NDVI decreased by 19.39%.It shows that different types of vegetation have various responses to the long-term effects of ground deformation in their growth state.(4)The long-term effects of ground deformation will lead to the degradation of tree to shrubs or herbs,accelerate the development and gathering of shrubs,and enlarge the fragmentation of vegetation pattern.The 30-year spontaneous succession of plant communities in study area under the original scenario and the ground deformation scenario are simulated and compared,with four initial conditions combined with gully and flat terrain conditions,high initial vegetation and low initial vegetation coverage conditions.Results show that the long-term effects of ground deformation on the plant communities' succession are mainly manifested in restricting the growth and development of trees,and making the deformed area the first to form a settlement area of shrub vegetation,and the originally compact vegetation pattern tends to fragment.Ground deformation has greater impact on vegetation in flat terrain areas than in gully areas,and has greater impact on vegetation in areas with low initial vegetation coverage than in areas with high initial vegetation coverage;it has the most obvious impact on the pattern of trees,while the NMSE is always greater than 0.5.The long-term effects of ground deformation on vegetation gradually weaken with the increase of vegetation coverage,and the difference between original scenario and ground deformation scenario will also decrease.(5)Designing long-term goals,managing long-term effects and implementing long-term supervision are the core ideas of the vegetation reconstruction system in mines considering the long-term effects of ground deformation on vegetation.According to the mechanism and characterisitics of the long-term effects of ground deformation on vegetation,four design guidelines of “suitabile action,long-term planning,concentrated management,and overall restoration” are put forward for designers of vegetation reconstruction system;a implementation framework of“monitoring,evaluation,simulation,planning,governance and feedback” are put forward for the implementers vegetation reconstruction system;three policy recommendations of “establishing the meachnisms of overall evaluation,long-term monitoring and real-time governance” are put forward for the regulators vegetation reconstruction system.To protect the ecosystem in mining area in its entirety,restore it systematically,and take a comprehensive approach,it is important to include the long-term effects of ground deformation on vegetation within the protection and restoration of mine ecosystem.An insight into the long-term effects of ground deformation on vegetation,will benefit to understand the comprehensive relationship between ecological elements and processes in mine ecosystem,and to provide a theoretical guidance and practical reference for formulating a new system for ecological restoration and vegetation reconstruction in mining area.This dissertation has 120 figures,34 tables and 271 references. |
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