| Nujiang Prefecture is the core area in the World Natural Heritage Site of Three Parallel Rivers.It is a biological gene pool and a geological and geomorphological museum in southwest China and even in the whole country,assuming ecological functions of strategic importance as well as a great responsibility for ecological protection.The main contradiction faced by the heritage site is to find a way to coordinate the sustainable development of economic and ecological environment in the site,and a comprehensive and thorough understanding of the ecological security in the site is the prerequisite for the coordination.In this regard,based on multiple spatial analysis technical platforms such as GIS and RS,in accordance with the characteristics of China’s ecological security research,upholding putting people first,and focusing on human survival and development security,proceeding from major ecological problems including geological disasters and soil erosion in Nujiang Prefecture,and featuring the structural safety of ecological system,the service ability of the ecosystem to meet various human needs and the safety of human activities to ecosystem,this thesis selects five comprehensive ecological safety indicators including geological disaster susceptibility,the amount of soil erosion and erosion intensity,the ecological security of landscape pattern,the potential for land production,and the value of ecosystem service functions to conduct multi-perspective and multi-dimensional dynamic evaluation and zoning of the ecological security of Nujiang Prefecture.The main conclusions are as follows:(1)From the perspective of the security of geological environment:The susceptibility of geological disasters in Nujiang Prefecture in various periods over the past 20 years is mainly in moderate and lower level,accounting for 92.5%,80.99%,and 80.31%respectively of the total area;areas with low and lower susceptibility are gradually reduced,and areas with medium and high susceptibility are gradually increased;spatially,areas with relatively higher susceptibility are largely distributed on banks of rivers and along the roads and other areas for human settlement,indicating salient security issues in human settlement and geological environment.Through the correlation and spatial comparison analysis of disaster susceptibility variables and indicator variables,it is concluded that the susceptibility pattern of geological disasters in Nujiang Prefecture is mainly controlled by slope roads,faults and land types.(2)From the perspective of soil environmental safety:The average amount of erosion per unit area in Nujiang Prefecture was 12.02t/hm~2 in 1996,7.11t/hm~2 in 2006,and 5.94t/hm~2 in 2016;the total soil erosion was 17.67×10~6t in 1996,10.45×10~6t in2006,and 5.94×10~6t in 2016,and the drop rate of total erosion during the three periods was 33%.Spatially,in 1996,soil erosion mainly took place on both sides of the Nujiang River,the Lancang River,and part of the high-altitude areas.In 2006 and2016,soil erosion on both sides of the Nujiang and the Lancang River was significantly reduced and effectively improved;soil erosion at high elevations on both sides of the Dulong River was gradually aggravated;generally,soil erosion in Nujiang Prefecture was slight erosion as it was not severe,there were,however,still a high or higher intensity of erosion,which should be taken seriously.(3)From the perspective of ecological security of landscape pattern:From 1996to 2016,the average ecological safety indexes of landscape pattern of all land types in Nujiang Prefecture as a whole were on the rise,indicating that the ecological safety of land types’spatial distribution pattern has been reduced;spatially,land types with relatively higher ecological safety indexes are mainly distributed in the areas along the banks of rivers;in county regions,Lanping and Lushui are the least safe;in terms of topographic differentiation,the ecological safety indexes of landscape patterns are on the decline with increasing altitude and slope.(4)From the perspective of ecosystem service function value:in terms of quantity structure,the value of service function has been decreasing from 1996 to 2016 with smaller declines,suggesting that the ecosystem service function of Nujiang Prefecture has been degraded in the past two decades;in light of spatial distribution structure,the spatial distribution of the value of service function in Nujiang Prefecture’s ecosystem mainly shows an increasing trend from southeast to northwest;from 1996 to 2016,the value of ecosystem service function in areas of all altitudes has been declining;the value of ecosystem service function at altitudes below 2000m and between3000m-4000m has been increasing,and those at altitudes between 2000m-3000m and above 4000m has been declining;with the increase of slope,the variations in the value of ecosystem service function in the three periods were basically the same,showing a linear and slowly increasing trend.(5)From the perspective of land and food production potential:In light of quantitative structure,the photosynthetic production potential of Nujiang Prefecture remained the same.From 1996 to 2016,the overall trend was decreasing,with an increase first and then a decrease;the productivity of the latter three increased gradually,which had something to do with climate warming;the decreasing degree of decay indicates that the potential land productivity in Nujiang Prefecture gradually increased and the ecosystem is able to produce more food;in terms of spatial distribution pattern,the distribution pattern’features of the land production potential of four types of land in three periods remained basically unchanged,and the photosynthetic productivity showed an increase from southwest to northeast,with smaller values gradually expanded northwards,indicating that the photosynthetic productivity was declining;the photo and temperature productivity showed a downward trend from valleys to high mountains;the distribution pattern of the climate productivity and the soil productivity was basically the same,exhibiting two patterns of characteristics,the overall trend is to decrease from valleys to high mountains and decrease from south to north.In general,the higher the elevation,the steeper the slope and the lower the potential for land production.(6)From the perspective of synthetic ecological security,over the past 20 years,the ecological environment security in Nujiang Prefecture has mainly been in a relatively low level,the ecological environment is relatively fragile,and the overall spatial distribution pattern of safety level in each period has been relatively consistent and stable with little variation;low-secure and insecure areas are distributed mainly in the Lancang River Basin,followed by areas near the coast of Nujiang and high altitude weed-grown and snow-covered areas in the northern part of Nujiang Prefecture.Lanping County is at the least ecological secure-low or lower level,with prominent ecological security issues;The Moran’I index of ecological safety was0.86,0.81 and 0.73,which showed that the distribution of ecological safety index was highly spatial self-correlation,while the value of Z was much greater than 2.58 and the value of P was less than 0.01 that shows an extremely significant pattern of aggregation;each year’s distribution of elevation of ecological security indexes is fluctuating as there is no continuous law of ascending and descending,and there is an obvious law of continuous increase as the slope increases.The formation of the ecological security pattern in Nujiang Prefecture is mainly affected by the composition control of ecological security in geological disaster susceptibility index,the ecological security index of landscape pattern,and the ecosystem function value.In planning and constructing ecological protection,decisions should be implemented reasonably according to the three security components. |
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