| Nowadays,the increasing global and regional environmental problems had become the main factors limiting the economic and social development of countries.The protected areas were one of the most direct and effective ways for human beings to deal with environmental problems.Due to human disturbances and the effects of climate change,the effectiveness of protection in some protected areas had been questioned.Extremely arid areas were one of the most vulnerable components of terrestrial ecosystems,and the desert ecosystems in which exhibit significant vulnerability and variability due to climate anomalies and human disturbances.Compared with other regions,the ecosystems in extremely dry environments had strong sensitivity and poor stability.The landscapes and ecological environments in which were more susceptible to human activities and climate changes.It was of great significance to scientifically and accurately assess the conservation effectiveness of the nature reserves under extreme drought conditions,and it had important reference value for the formulation and optimization of conservation strategies,and it had very important practical significance.However,relevant research mainly focused on the effectiveness evaluation of nature reserves in humid and semi-humid environments,and there were relatively few studies on the effectiveness evaluation of nature reserves in extremely dry environments.Therefore,taking the four protected areas along the Shule River in Dunhuang as examples,an evaluation system and model suitable for the nature reserves in extremely dry environments were established.And the four protected areas were evaluated for protection effectiveness.In the evaluation,based on the Landsat TM/OLI images,field measured data and high resolution images,the information of ecological landscapes from 1986 to 2015 were extracted with a random forest model.And the classification results were visually interpreted to correct the accuracy requirements of the study.A comprehensive evaluation system and model for the protection effectiveness of nature reserves was established based on comprehensive analysis of the protected areas in the study area.And the characteristics of the landscape pattern,the temporal and spatial distribution characteristics of the main protection objects and the temporal-spatial variation characteristics of human activities of the four protected areas for nearly 30 years were quantitative analysis.On the basis of the above,a comprehensive analysis of the protection effectiveness of each protected area were carried out.The main work carried out in this paper and the main conclusions were as follows:(1)A two-level comprehensive evaluation system with 7 indicators(such as landscape types conversion index et al.)based on landscape conservation,main protection object and protection stress including was established.The evaluation system and indicators established in this paper could reflect the protection effectiveness of Dunhuang Nature Reserves to a certain extent,and had certain applicability in other nature reserves in extremely arid regions.The seven indicators constructed in this paper reflected the protection effectiveness of Dunhuang Nature Reserve from the aspects of landscape conservation,protection objects and protection coercion,and provided scientific reference for improving the follow-up monitoring of protected areas,and other natural reserves under extreme drought conditions.(2)Although the landscape pattern of nature reserves in Dunhuang had always been dominated by deserts and grasslands,forest land and wetlands had shown an increasing trend,especially artificial landscapes.In the past 30 years,the desert area of the Xihu National Nature Reserve had increased,the area of grassland had decreased,the area of forest land and wetland had increased slightly,and the area of artificial landscape had increased significantly.The wetland area of the Nanquan wetland Nature Reserve increased slightly,the area of grassland increased,the area of forest land accounted for a small,and also increased,the area of artificial landscape increased,and the area of desert decreased.The area of wetlands,woodlands and artificial landscapes in the Donghu Nature Reserve increased,and the area of grasslands and deserts decreased.The forest land and artificial landscape area of the Beihu protected area had increased,the wetland had been slightly reduced,and the grassland and desert area had significantly reduced.(3)The monitoring results of spatio-temporal changes of protected objects showed that the changes of vegetation and wetland were basically consistent with the rhythm of precipitation changes,indicating that precipitation played a central role in the ecological environment changes in extremely arid regions.The analysis of spatio-temporal changes of protected objects showed that the wetland area of Xihu National Nature Reserve and Nanquan Wetland Nature Reserve had a trend of “increasing-decreasing-increasing”,and the change were basically consistent with the trend of precipitation in the study year,indicating that the precipitation changes had a significant impact on the wetland areas in the protected areas under extreme drought conditions.The plant community in the protected areas had a simple structure,a low plant diversity,and a low vegetation NDVI value.Except for the Xihu National Nature Reserve,the vegetation NDVI of the other three protected areas were all fluctuating upwards from 1986 to 2015.And the change areas of the vegetation were spatially different.(4)The area of human activities and the number of plaques in the protected areas all showed an increasing trend.Although the increased parts were different,the closer they were to the artificial oasis and the traffic lines,the more obvious the increase.The human activities of the Xihu National Nature Reserve were mainly distributed in the buffer zone around the northeast corner of the reserve.The distribution of human activities in Nanquan Wetland Nature Reserve presented the characteristics of buffer zone > core zone > experimental zone.The Donghu Nature Reserve and the Beihu protected area were mainly distributed near artificial oases and major transportation lines.The results of human activity interference index analysis showed that the impacts of human activities in different protected areas were different,but they all showed an increasing trend.And the closer to the artificial oasis and the main traffic routes,the more types of human activities,the larger affected areas.(5)The protection effectiveness of each protected area were different,basically at the level of“normal effect”,“basic maintenance” and “slightly better”.Specifically,the effectiveness of the landscape conservation of the Xihu National Nature Reserve was basically maintained,and the main protection objects showed a slight improvement,and the impacts of human activities increased slightly.The overall protection effectiveness were general.The effectiveness of the landscape conservation of Nanquan Wetland Nature Reserve was basically maintained,and the main protection objects were slightly improved.However,due to the slight increase in human activities,the comprehensive protection effectiveness of the protected areas was basically maintained.Although the impacts of human activities had increased significantly in the Donghu Nature Reserve,the effectiveness of landscape conservation and the main protected objects had improved slightly,and the comprehensive protection effectiveness of the protected areas had improved significantly.The effectiveness of the landscape conservation of the Beihu protected area had been basically maintained,and the effectiveness of the main protection objects had been significantly improved.Due to the significant increase in human activities,the protection effectiveness were generally maintained.The above showed that in the extremely dry environment,it was a long way for the protection effectiveness of Dunhuang Nature Reserves to achieve "significant improvement". |
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