| The desert-oasis ecotone in the middle reaches of Heihe River is located in the middle of Hexi Corridor,which belongs to the arid area of Northwest China.The desert-oasis ecotone plays an important role in controlling desertification and maintaining ecological security of oasis.However,because it is located in the ecotone of desert ecosystem and oasis ecosystem,the natural environment is harsh and the ability to be affected by external interference is weak,which makes it a vulnerable and sensitive ecology Area.The structure of the vegetation community on the ecotone is simple,but the effect of wind and sand fixation is significant.This paper takes the vegetation landscape of The desert-oasis ecotone in the middle reaches of Heihe River as the research object,based on"3S"technology and FRAGSTATS 4.2 software,and takes the Landsat TM image in 2008,2010,2012,2014,2016and 2018 as the Basic data.The vegetation coverage(f_c)is divided into six levels:bare land(f_c?5%),medium low vegetation coverage(5%<f_c?20%),low vegetation coverage(20%<f_c?40%),medium vegetation coverage(40%<f_c?60%),medium high vegetation coverage(60%<f_c?80%)and high vegetation coverage(f_c>80%).The present situation and dynamic change of vegetation landscape pattern were analyzed quantitatively by landscape index method,and the driving factors of dynamic change of vegetation landscape pattern are analyzed by using grey correlation analysis.The main research results are as follows:(1)The dominant landscape in the study area is the high vegetation coverage landscape;the most serious fragmentation is the middle vegetation coverage landscape,and the less fragmentation is the bare land and high vegetation coverage landscape.In 2010,each vegetation landscape type had the smallest patch fragmentation,the lowest landscape heterogeneity,the smallest edge segmentation,the smallest possibility of edge effect,and the smallest frequency of alternation between landscape types,followed by the smaller fragmentation of each landscape type,and the lower landscape heterogeneity was in 2014 and2016.(2)During the period of 2008-2018,the vegetation landscape area with f_c?40%and f_c>80%showed an increasing trend,the increased area was 45.71 hm~2 and 1.26 hm~2respectively,and the volatility of landscape patch fragmentation decreased;the vegetation landscape area with f_c?40%and f_c>80%showed a decreasing trend,and the volatility of landscape patch fragmentation increased.At the landscape level,from 2008 to 2018,the fragmentation and heterogeneity of vegetation landscape patches decreased,the patch shape changed steadily,and the connectivity of landscape patches increased.(3)In the transformation of vegetation landscape types in 2008-2018,the main area of non transferred landscape is high vegetation coverage(fc>80%),while the main area of transferred landscape is medium low and medium vegetation coverage(20%<f_c?60%).During the period of 2008-2014,the area of degradation was larger than that of evolution,and vegetation landscape deteriorated.In 2014-2018,the area of evolutionary evolution is larger than that of degradation,and the vegetation landscape has improved.(4)The main meteorological factors affecting the dynamic change of landscape pattern of bare land are relative humidity,sunshine duration and evaporation;The main meteorological factors affecting the dynamic change of vegetation landscape pattern of 5%<f_c?40%are precipitation,evaporation and sunshine duration.The main meteorological factors affecting the dynamic change of vegetation landscape pattern of f_c>40%areprecipitation,relative humidity and sunshine duration.(5)The shallow soil moisture(0?40 cm)and deep soil moisture(80?120 cm)have a great influence on the dynamic change of vegetation landscape pattern.The deep soil moisture which has a great influence on the dynamic change of vegetation landscape pattern with f_c?20%is 80-100 cm,and the deep soil moisture which has a great influence on the vegetation landscape pattern with f_c>20%is 80-120 cm.The soil organic matter of 40 cm soil layer has a great influence on the dynamic change of vegetation landscape pattern. |
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