| The geomorphology of the karst trough valley is mainly distributed in the karst area of Southwest China.The topography is complex,the terrain is rugged,and the ecological environment is extremely fragile.Its ecosystem is restricted by its topography and landform,and land degradation is serious;In addition,the box-type tight northeast anticline /slope structure in the trough valley area is developed,and the rock structure tectonic angle changes greatly.It is controlled by a variety of lithologies,forming topographic fluctuations,high height differences,and hillsides,troughs and basins alternate in space Appearance,the terrain differentiation is obvious,forming a highly heterogeneous landscape feature.This paper mainly selected three representative karst trough valley areas at the junction of Dejiang,Yanhe,and Yinjiang counties in Guizhou Province,China.With the help of 3S technology,the DEM data and land use status data in trough valley area was extracted,and a systematic analysis was performed from 2005 to 2017.Land use change in three troughs and the overall evolution of landscape ecological security,based on which,the land use changes and landscape pattern evolution characteristics of different landform types in each buffer zones,and the landscape pattern evolution characteristics of main land use types was explored.(1)Overall characteristics of land use change in trough valley areaFrom 2005 to 2010,the land use showed the increase of shrubbery,woodland,grassland,upland,cultivated land and urban land.From 2010 to 2014,this stage was mainly in the stage of trough valley ecological restoration.Under the influence of the policy of returning farmland to forest and the control of rocky desertification and other projects,there was a trend of the transformation of mountain dry land,paddy field and grassland into forest land,urban land and rural land in the trough valley area.From 2014 to 2017,this stage is mainly in the period of rural revitalization and targeted poverty alleviation.In response to the construction of ecological civilization,the cultivated land with the main production function is transformed into the economic and ecological fruit forest.In the overall period from 2005 to 2017,the dynamic change characteristics and utilization degree responses of land use types in trough valley area showed common characteristics and differences.(2)Variation characteristics of land use in the trough valley area on topographic factorsThe land use change in the karst trough valley shows a gradient effect under the action of topographic factors,and the spatial distribution pattern of land use is closely related to the topographic factors.During the period from 2005 to 2017,in low-level elevation,slope,topographic relief and topographical level areas,the distribution of rural residential land,urban land,mountain dry land,paddy fields and roads in the troughvalleys of the western,middle,and eastern parts of the country has forest land,Shrubs and grasslands,grasslands are mainly distributed in higher terrain grades.With the increase of elevation,slope,terrain relief and terrain level,the land use type gradually showed unity.(3)Landscape pattern of trough valley and its overall characteristics of ecological securityFrom 2005 to 2017,the trough valley patch density(PD),patch marginal density(ED)and maximum patch index(LPI)in the western,middle and eastern regions showed increasing changes,and the landscape shape index(LSI)was stable,mainly concentrated in the flat part of the channel dam.The aggregation index(AI)in the trough valley area in the eastern of the western was gradually reduced and dispersed from the trough dam to the hillside,while the aggregation index(AI)in the middle valley was extended from the trough dam to the hillside,and the patch dispersion degree was increased and the sprawl index(CONTAG)was enhanced.During the period from 2005 to 2017,the distribution index and diversity index of scentiness evenness and scentiness evenness in the channel valley area were concentrated in the flat channel dam,and the slope of the channel dam extended in an uneven state,with a simple landscape space structure and a single diversity.The ecological security of the trough valley in the west and east gradually increases from the trough dam to both sides of the hillside,while themiddle valley is opposite.The spatial autocorrelation degree of the ecological security of the trough valley in the west was weakened and the spatial differentiation was enhanced,while the spatial convergence and autocorrelation degree of the middle and east valleys were gradually enhanced.(4)Land use and landscape pattern evolution of different buffer zones in trough valley area.With the increase of buffer distance,the land use diversity index of the trough valley in the west,central and eastern regions showed the change feature of continuous decrease.Among them,the diversity index showed the change feature of 2017 > 2014> 2010>2005.With the increase of the buffer zone,the land use index of the trough valley in the west-middle and eastern regions showed a decreasing trend.Between 2005 and 2017,western trough valley>eastern trough valley>middle trough valley.The spatial heterogeneity of landscape fragmentation and diversity in the trough valley region in the west-central and eastern regions is most concentrated in the buffer distance range of0~1000m.With the increase of buffer distance,the fragmentation and diversity of landscape patches decrease.(5)Driving factors of land use change and landscape pattern evolution in trough valley areaThe influence of land use change in trough valley area is the result of natural,social and economic effects,in which the topography is the directfactor,the social economy is the driving factor,and the policy orientation is the redistribution factor.The factors influencing the evolution of landscape pattern in valley area are the distance from town and the distance from road,among which the two factors have the greatest influence on the fragmentation and diversity of landscape pattern,followed by the elevation,slope and topographic relief of natural factors. |
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