Landscape Pattern Change And Ecological Security Assessment Of Pengzhou In Chengdu

Pengzhou is one of the key nourishing ecological areas in Chengdu-Chongqing Region.The ecological safety of Pengzhou shows close relationship with the sustainable development of Chengdu,as well as urban development in Chengdu-Chongqing Region.As affected by natural and artificial factors,the ecological environment of Pengzhou is facing severer and serverer challenges.It becomes of great importance to study the landscape pattern analysis and ecological security assessment of Pengzhou.Involving the use of the Landsat data of 1996,2001,2007,2010 and 2013,the regional landscape database of Pengzhou were set up through the QUEST decision-tree classification model.Subsequently,the characteristics and driver factors of landscape pattern of Pengzhou were studied through the methods of spatial analysis,landscape index analysis and principal component analysis based on GIS.The ecological security evaluation index system of Pengzhou was set up through the PSR model.The weight of each parameters was determined by the method of AHP.Finally,the ecological security of Pengzhou in 2007,2010 and 2013 was evaluated by the method of ESI.Further suggestions and measures for ecological safety protection were also proposed.The main results were as follows:(1)Significant changes for landscape type of Pengzhou from 1996 to 2013 were observed.There was a decreased trend for the forest land,agricultural landscape and water landscape,while a rapid growth trend for the construction landscape.The bare soil landscape tended to an increasing trend after an ascension and reduce process.The forest land and agricultural landscape,which account for more than 80%of the total area,dominated all landscape types in Pengzhou,followed by bare soil landscape,construction landscape and water landscape.From 1996 to 2007,the forest land was the main source for landscape type conversion,accounting for 50.06%of the total conversion.The forest land was mainly converted to agricultural landscape,and the conversion area was up to 6568.70 hm~2.The construction landscape was mainly converted from agricultural landscape,with the conversion area of 1563.30 hm~2.From 2007-2013,the forest land and agricultural landscape were the main sources for landscape type conversion,accounting for 44.97%and 44.09%of the total conversion.The forest land was mainly converted to bare soil landscape and agricultural landscape,and the bare soil landscape was also converted to forest land in turn.The agricultural landscape was mainly converted to construction landscape,and the conversion area reached 8492.50 hm~2,therefore showing obvious unipolarity.(2)A drastic change for landscape pattern of Pengzhou from 1996 to 2013 was observed.In view of landscape type,the dominance of the forest land and agricultural landscape showed a decreased trend.The construction landscape spread outward continuously with an increasing dominance and a reduced patch density.After 2007,there was an increasing patch density for the bare soil landscape,forest land and agricultural landscape.There was also a great increase for the edge density of the forest land,construction landscape,bare soil landscape and agricultural landscape with more complex edge shapes.From the point of landscape,the patch density and landscape shape index decreased first and then increased,and the minimum values were observed in 2007,demonstrating that the landscape fragmentation and complexity decreased first and then increased.Shannon’s diversity index(SHDI)and Shannon’s evenness index(SHEI)tended to an increasing trend after a first increase and then decrease,showing an enhancing landscape heterogeneity in late ages.The changes of the contagion index(CONTAG)indicated that the dominant landscape type presented the best connectivity in 2007,after which less connectivity was observed.(3)The landscape pattern changes of Pengzhou were affected by natural and artificial factors.In terms of the natural factors,more than 75%of construction landscape and 79%of agricultural landscape were located in the plains,and more than 84%of forest land was located in mountainous region.These indicate that geomorphic type is the foundation of landscape pattern in Pengzhou.Natural disaster was the main cause for drastic changes for landscape pattern of Pengzhou in a short period.After the 5·12 Earthquake,the forest land and agricultural landscape decreased 8093.70 hm~2 and 6219.81 hm~2 till 2013,while the construction landscape and bare soil landscape increased 8326.35 hm~2 and 6408.90 hm~2 till2013.In terms of the artificial factors,population growth,economic level and policy were the main causes for landscape pattern changes in Pengzhou,and also the most direct driving factors for urban construction and infrastructure construction development and more fragmentation for agricultural landscape.(4)There was a decreasing trend for the ecological security level in Pengzhou from2007-2013 with the average composite index of 59.79,56.28 and 55.09.The ecological security level mainly dominated by the less safe level and critical region.The critical region was also converted into low ecological security region,resulting in less and less areas for the high ecological security regions,which accounted for 27.09%,23.40%and 19.54%of the total area.Meanwhile,there were also significant spatial differences for ecological security hierarchy.The ecological security hierarchy of the plains was greater than that of the hills,followed by the mountains.There was a decreasing trend for the ecological security hierarchy from the southeast to the northwest.The high ecological security regions were found in Shengping Town,Sanjie Town and Jiuchi Town.The ecological security of Tianpeng Town,Zhihe Town,Longfeng Town and Danjingshan Town presented a decreasing trend,even decreased to a less safe or unsafe level.Longmenshan Town,Tongji Town,Cifeng Town and Xiaoyudong Town presented a low ecological security.In especial,the ecological security of Longmenshan Town was even unsafe.In future,the ecological security protection of Pengzhou had better focus on eco-environmental frail zone in mountain areas and Qianjiang Basin along with land resource management.