| Land-use and landscape change are important aspects of regional environmental change research in arid areas,and are of great significance to the stability and sustainable development of oasis.Oasis,desert-oasis ecotone(DOE)and desert compose the typicallandscape structures in arid regions.Few previous studies took these three landscape types as a whole to study the spatio-temporal characteristics of landscape changes and their mutual transformation.The middle reaches of Heihe River Basin(HRB),a typical endorheic basin in northwest China,was taken as the study area.Using the land-use data from 1990,2000 and 2010,the oasis land-use dynamics before and after the implementation of Heihe Water Diversion Project in the middle reaches of HRB was analyzed.Based on Landsat image data of six periods from 1990 to 2015,this study extracted the information of oasis,DOE anddesert by combining the decision tree classification algorithm with visual interpretation,detected the spatio-temporal dynamics of landscape structure in the middle reach of HRB from 1990-2015,and identified the key driving factors for landscape structure changes and quantify their contributions.The main conclusions are as follows:(1)More than 70% of the land in the middle reaches of HRB is unused land,and the area of cultivated land accounts for more than 15%,followed by grassland and artificial surface.In each study period,great changes occurred in wetland,cultivated land,artificial surfaces and grasslands,and the land use change from 1990 to 2000 is significantly stronger than that from 2000 to 2010.During 1990-2010,the area of cultivated land and artificial surface increased obviously,while the area of grassland and unused land decreased.The increased area of cultivated land mainly came from unused land(bare land and sparse grassland),while much cultivated land transformed to unused land(sparse grassland),grassland and woodland.(2)During 1990-2015,the landscape change is characterized by oasis expansion(+37.21%) in a one-way transition with an unbalanced status,while the DOE(-12.73%)and desert decreased(-8.50%).The mutual transformations among them were frequent and drastic,and mainly occurred in the periphery of oasis,but the oasisization is much stronger than desertification.In addition,the fragmentation and irregularity degree of patch shape in the middle reaches of HRB decreased,and the composition and structure of landscape tended to simplify.(3)The area of oasis in the middle reaches of HRB has a significant positive correlation with population,GDP,annual average temperature or river flow at Yingluoxia,and a high negative correlation with groundwater table.The direction of correlation between the area ofDOE and other factors or the area of desert andother factors is opposite to that between the area of oasis and other factors,and there is a significant positive correlation between the area of DOE and groundwater table;The landscape structure changes from 1990-2015 in the middle reaches of HRB were mainly driven by population,river flow and gross domestic product with the unique contributions of 35.99%,9.01% and 7.68%,respectively,and the cumulative contribution of 96.64%.It is recommended that local government and farmers should pay attention to the protection of nature vegetation,and government should enhance the management of water resources and appeal to farmers to use water resources reasonably and efficiently to ensure the ecological stability of the fragile arid region. |
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