| The regional ecological risk assessment is as a branch of ecological risk, Regional ecological risk assessment aims to forecast the probable negative impact in the feature of all sorts of disasters or accidents to the natural environment and ecosystems at the regional scale, Heihe River basin is a typical inland river in the northwest arid area, However, because of the influence of human activities, social and economic development, basin has a serious ecological problem. In this paper, combining land use, landscape pattern and ecological risks is to analyze the uncertainty risk of ecosystem and the size of ecologically harmful levels. Ultimately, it provides technical support and scientific basis for ecosystem management in Heihe River Basin.In this study, with the technical support GIS and RS, human activities is as risk sources, Selecting farmland, woodland, grassland, residential and industrial land, unused land and waters and the six types of landscape and other representatives ecosystems as a risk receptor, basing on landscape pattern and landscape ecology loss Index decided ecological risk assessment index, thus, establishing the landscape ecological risk index as a measure of the end of ecological indicators, it reflects the human interference degree for different types of representative landscape ecosystems and ecological risk dynamics of evaluation Basin. The main conclusions are:(1)From 1986 to 2000, the general trend of land use change in upper and middle reaches of Heihe basin was that forest land, meadow and water area were decreasing; while cultivated land, unused land, and the land use of urban and rural, inhabitant and industrial were increasing. These changing processes of land use led to the decrease of ecosystem service values in this area. From 2000 to 2011, the general trend of land use change is that forest land; meadow, cultivated land, and the land use of urban and rural, inhabitant and industrial were increasing; while water area and unused land were decreasing, which made a partial improvement of ecosystem service values in the area. From the changes in the spatial distribution,The cover area of natural vegetation, forest land and meadow in upstream continues to decline. Though recovered a little, the land uses of cultivated land, and urban and rural, inhabitant and industrial were continuously extending, suggesting that there is a further deterioration in ecological environment. The oasis farming in the middle reaches area made a great development; but at the same time, the land use of forest land and meadow were increasing, and the rate of the water area’s decrease was slowing down due to the policies effect of China Western Development, and Grain for Green Project in the area. So, we can see that ecological risk was reducing slightly, and the ecological environment become a little better than before.(2)Patch levels analysis showed that the patch number and area of arable land have increased since 1986. The areas of woodland were decreased in the first stage, and it showed recovery state in the second stage. However, as a result of serious deforestation, that area is eventually presented a reduced state. Changes of the area of grassland patch had a similarity to woodland, but the main reason for this change was grazing. The patch areas of unused land were increased first, and then decreased. The patch areas of waters were reduced continuously, while the patch areas of the urban-rural land, residential and industrial area are inversely proportional to waters patch. Patch types analysis showed that the dominance of arable land patch was decreased after an initial increased, and its dominance was a small portion in a whole drainage basin. Change of the dominance of woodland patch was relatively stable, and it was more complex for grassland patch. The dominance of grassland was taken on a substantial increase and then dropped sharply, but its predominance in a whole drainage basin was unshakable. The dominance of urban-rural land patch was showed growth trend, dominance of residential and industrial area patch had the similar trend. It was inseparable from the land expansion caused by urbanization. The maximum patch index of unused land has been declining all the time, and its dominance was faded away.(3)From the analysis of space characteristics of ecological risk, the high risk level areas are mainly distributed in the landscape in residents and industrial and mining land, unused land and cultivated land and so on. Low level risk areas are mainly distributed in the woodland and grassland landscape. Residents and industrial and mining land are pure human landscape, are the largest affected by human activities, so is the highest ecological risk. Cultivated land is the second landscape affected by human activities, the change of the landscape characteristics completely controlled by the human, therefore its ecological risk is higher. Cultivated land is stronger landscape affected by human activities, the landscape characteristics changes completely controlled by human, so the ecological risk is higher. Unused of vegetation coverage is extremely low, bare rock, and the ecological environment is fragile, easy to be damaged after disturbance by human activities, so the ecological risk is higher. From the analysis of time characteristics of ecological risk, the ecological risk change is divided into two stages: Ecological risk value increased from 1986 to 2000, ecological environment deteriorate faster; from 2000 to 2011, the ecological risk value decreased, the ecological environment is on the mend. Heihe river shelter-forest region is very strong between landscape types between the degree of conversion in the last 25 block. This is mainly due to the Heihe river basin has caused in the process of forest land, grassland destruction after middle region in the 80 s, causing the heihe river basin ecosystem deterioration occurred. Response to the regional policy after returning farmland to forest and grassland, this area has a good improve ecological environment in the 20 th century, especially the downstream area. Due to the influence of terrain, upstream region is not easy to recovery, making the region’s ecological improvement with a lag. From the analysis of county scale ecological risk, the ecological risk value of Zhang ye city, Yu gu autonomous county, Qilian county, Lin Ze county, Jia yu guan city and Jia yu guan city, Gao tai county change is first high then low. Ecological environment change is first deteriorated and later improved. The change of the ecological risk value of Shan dan and Min le is increasing, it means the ecological risk is deteriorating. The ecological risk value of Tian jun and Gang cha is low, maintaining a good ecological environment.Finally, according to different risk grade, different ecological risk management countermeasures are put forward. This research has important practical and guiding significance to heihe river shelter-forest regional ecological security. |
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