Study On Landscape Pattern Change And Ecological Quality Assessment Of North Mountain Area In Lanzhou

With the development of economy,the demand of urban construction land is increasing.Lanzhou city is constrained by the terrain of"two mountains and one river",and the construction land is particularly tense.In this context,in order to expand the scope of urban construction,Lanzhou city will focus on the north mountain area of Lanzhou.In the nineties of last century,Lanzhou city began to build Jiuzhou Development Zone in luoguogou,mainly by land creation to expand the urban area.In 2012,Lanzhou City determined the"comprehensive development project of low hills,gentle slopes,gullies and other unused land",and planned comprehensive development pilot zones in the northern mountain area of Lanzhou,which are Qingshi area,Yanchi-Miaoercha area,and Shazhong-Shengou area.In recent 30 years,with the increasing area of land creation project,the land creation project has changed the original landscape pattern and ecological quality.Therefore,it is necessary to study the landscape pattern change and ecological quality of north mountain area.This paper firstly analyzes the scope of land creation,secondly;Secondly it calculates the landscape level index and patch type level index in the typical areas of land creation,and analyzes the process of landscape pattern change in Lanzhou northern mountain areas;Finally,based on the Landsat images in 1991,2001,2009 and 2016,the normalized vegetation index(NDVI),humidity index(WET),surface heat(LST)and dryness(BCI)were extracted to construct the remote sensing ecological index(RSEI)and and the temporal and spatial changes of ecological quality were analyzed.The main conclusions are as follows:(1)From 1991 to 2016,the land area of the project increased by about 220 km~2,of which,from 1991 to 2000,the new area increased by 9.7 km~2,with an average annual growth of 0.97 km~2,and the growth trend was slow;from 2001 to 2008,the new area increased by29.74 km~2,with an average annual growth of 2.94 km~2,and the expansion rate gradually increased,showing a multi center expansion mode;from 2009 to 2016,the new area increased by 180.41 km~2,with an average annual growth of 30.07 km~2,and the spatial distribution was wide.In the past 30 years,the center of gravity of land creation area has shifted 16km northward,which indicates that northward development has become the main direction of urban space expansion in Lanzhou.(2)From 2000 to 2016,there were significant differences in the change process of different landscape indexes in the typical area of Northern Mountain in Lanzhou,which mainly showed that the number of patches,patch density,landscape shape index,fragmentation index and diversity index increased year by year;the largest patch index,spreading index and aggregation index decreased year by year;the perimeter-area fraction dimension showed an overall trend that first decreased and then increased.It indicates that the landscape pattern presents the trend of fragmentation and complexity on the whole.(3)From 1991 to 2016,the RSEI of Lanzhou northern mountain area increased from0.297 to 0.406,,and increased by 36.7%in 26 years.In the study area,the proportion of areas with excellent and good ecological status in the total area increased from 7.52%in 1991 to11.72%in 2016,and the proportion of areas with poor and quite poor ecological status in the total area decreased from 83.72%in 1991 to 64.12%in 2016.On the whole,the quality of ecological environment has been improved.However,the RSEI of the land creation area decreased from 0.229 to 0.105.Through the analysis,it can be seen that the increase of bare land and the decrease of vegetation coverage are the main factors causing the decrease of RSEI,and it indicates that the land creation project has a certain impact on the quality of ecological environment.