尼泊尔生态系统质量评估与时空格局变化——基于参照条件的评估方法

良好的生态系统质量是维持人类社会供给需求和可持续发展目标实现的重要保障。针对尼泊尔自然地理环境复杂多样，区域间气候差异明显的特点，结合基于参照条件的评估方法可以得到生态系统质量的相对水平值，其结果能够反映出不同的变化信息。植被是区域生态系统质量变化的重要指示器，利用尼泊尔五大地理区以及四种主要植被生态系统类型划分出20个生态评估区，从表征植被生态系统的水平结构、生产功能和垂直结构3个方面计算生态参数相对密度指标（RVI），结合主成分分析法构建植被生态系统质量指数（VEQI），并以其国家自然保护区为参照，构建基于参照条件的生态系统质量评估模型，计算了尼泊尔2016和2020年基于参照条件的植被生态系统质量指数（VEQI''）并分析其生态系统质量的时空格局变化。结果表明：（1）2016至2020年，尼泊尔生态系统质量现实值VEQI的平均值增加了3.49%，总体上，在参照生态系统质量（VEQI_ref）提高（约1.41%）的背景下，生态系统质量相对水平值VEQI''增加了1.42%；（2）对于尼泊尔地区，评估区89%分位数的VEQI与其对应的国家自然保护区的参照值具有很强的相关性，总体差异较小，可以代替作为参照值；（3）从空间格局变化趋势来看，尼泊尔生态系统质量变好、基本稳定和变差的面积分别占植被生态系统总面积的74.16%、14.25%和11.59%。与数量不足、较难收集利用的野外观测台站数据相比，国家自然保护区更接近理想参照生态系统的假设，通过有限的自然保护区确定生态评估区的参照值，实现生态系统质量的快速评估，其结果具有更好的时空可比性，可以为区域生态质量变化评估及量化分析等方面提供参考。

Evaluation of ecosystem quality based on reference conditions and analysis of Spatio-temporal pattern changes in Nepal

Premium ecosystem quality is an important guarantee for maintaining the supply and demand of human society and achieving sustainable development goals. Aimed at complex and diverse naturally geographical environment and obvious climate difference between regions in Nepal, the evaluation method based on reference conditions can obtain the relatively horizontal value of the ecosystem quality, which can reflect the different changing information of regions. Vegetation is an important indicator of changes in the quality of regional ecosystems. In view of the characteristics of large differences in altitude and climate conditions and rich vegetation types in Nepal, this study proposed a method of ecosystem quality evaluation based on the reference conditions and then analyzed its spatio-temporal pattern changes. First, twenty ecological assessment units were divided by five major geographical divisions and four main vegetation types in Nepal, meanwhile the relative vegetation index (RVI) was calculated from characteristics of three aspects of vegetation ecosystems:horizontal structure, production function and vertical structure. Then, a new vegetation ecosystem quality index (VEQI) was constructed by using the method of principal component analysis, and the ecosystem quality evaluation model based on reference conditions was constructed according to the reference areas from many national parks, wildlife reserves and nature reserves in Nepal. Finally, the vegetation ecosystem quality index based on reference conditions (VEQI'') was calculated and it''s spatio-temporal pattern changes was analyzed in 2016 and 2020. The results showed that (1) from 2016 to 2020, the average real value of Nepal''s VEQI changed from 50.95 to 52.73, increased by 3.49%; the overall mean of VEQI'' changed from 76.24 to 77.32, increased 1.42%; on the whole, the VEQI'' improved in the context of improved reference ecosystem quality (VEQI_ref) (about 1.41%). (2) Using the 89% quantile of VEQI in ecological assessment areas as the reference values had a strong correlation with it''s national protected areas. Consequently, we used them to replace as the reference values of the ecological assessment areas when the number of pixels in the reference area was small or the data quality was not good. (3) From the perspective of spatial change, the areas where ecosystem quality improved, basically stable and worsened in Nepal accounted for 74.16%, 14.25% and 11.59% of the total area of vegetation type ecosystems, respectively. Compared with data from field observation stations that are insufficient and difficult to collect and utilize, national nature reserves are closer to the assumption of an ideal reference ecosystem, rapid assessment of ecosystem quality can be achieved by determining the reference value of the ecological assessment area through limited nature reserves. This kind of evaluation method based on reference conditions can eliminate the differences in ecosystem quality caused by vegetation properties and natural geographical conditions and it''s calculation results are more comparable in time and space, which can provide reference for regional ecological quality change assessment and quantitative analysis.