近40年青藏高原生态格局演变及其驱动因素

20世纪80年代至今近40年间，青藏高原自然与人工生态系统发生了广泛而深刻的变化，作为我国重要的生态屏障，亟需对其生态系统格局演变过程及其驱动因素进行系统定量的解析。本研究利用1980年至2018年间8期遥感解译土地利用与覆被数据，将青藏高原9类主要生态系统类型，森林、灌丛、草地、农田、城镇、水体与湿地、冰川、裸地、荒漠，依其主要构成组分，划分为以植被为主体的自然生态系统（森林、灌丛、草地）、以无机环境为主体的自然生态系统（水体与湿地、冰川、裸地、荒漠），以及人工生态系统（农田、城镇）共三大类。统计分析表明1980至2018年的近40年来，青藏高原以植被为主的自然生态系统面积约占61.9%，其中草地生态系统变化率较大，局部年际变化逾30%/10a，草地灌丛面积扩张明显，最高可达约7%/10a。此外，青藏高原喜马拉雅山脉附近的冰川消减较快，下降速率约达25%/10a。青藏高原东缘向西城镇扩张明显，城镇面积占比增加约40%。研究还对气温和降水计算其变化速率，量化驱动生态系统演变的外部气候环境的时空动态特征，结合地理环境变量、人类活动强度、土壤侵蚀度、生物丰度等综合的驱动因素指标，建立多层级结构方程模型。研究发现，以植被为主的自然生态系统变化速率与气温、降水的变化速率呈现显著负相关，以无机环境要素为主的自然生态系统与气候因子的变化速率呈现显著正相关，人工生态系统则与外部环境因素耦合关系不强，结果表明青藏高原森林、灌丛、草地一类自然植被生态系统与环境变化之间呈现负反馈的保守性耦合关系，相比较水体与湿地、冰川、裸地和荒漠生态系统来讲，具有更强的韧性，因此保护区域自然植被将有利于维护青藏高原整体的生态屏障功能。

Evolution of ecological patterns and its driving factors on Qinghai-Tibet Plateau over the past 40 years

From the 1980s to the present, the natural and artificial ecosystems of the Qinghai-Tibet Plateau have undergone extensive and profound changes. As an important ecological barrier area in China, it is essential to systematically and quantitatively analyze the evolution of the ecosystem patterns and its driving factors. In this study, 8-periods datasets from 1980 to 2018 of the land use and cover change based on the satellite remote sensing imagery interpretation were used to reclassify 9 major ecosystem types on the Qinghai-Tibet Plateau, including forest, shrub, grassland, agricultural land, urban, waters and wetland, glacier, bare land, and desert. According to their main components, they were divided into the natural ecosystems dominated by vegetation (forest, shrub, and grassland), and the natural ecosystems dominated by inorganic environment (waters and wetland, glacier, bare land, and desert), and there was another type of artificial ecosystems (agricultural land, and urban). The statistical results showed that from 1980 to 2018, the area of natural ecosystems dominated by vegetation accounted for about 61.9% of the Qinghai-Tibet Plateau. Among the natural vegetation, the grassland has fluctuated largely with the changing rate exceeding 30%/10a. The shrub expanded significantly and raised up approximately 7%/10a. The area of glacier near the Himalayas Mountains have been declining rapidly, with a shrinking rate of approximately 25%/10a. On the eastern edge of the Plateau, the urban has expanded to the west significantly, as the proportion of urban areas has increased by about 40%. We calculated the changing rate of the temperature and precipitation to quantify the spatio-temporal characteristics of the external climatic environment that drove the evolution of the ecosystems. Combined with the other comprehensive driving factors including geographical factors, human activity intensity index, soil erosion degree, and the biological abundance, we established a multi-level structural equation model. The results indicated that the changes of the natural ecosystems dominated by vegetation was significantly negatively correlated with the changing rate of temperature and precipitation, while the changes of natural ecosystems dominated by inorganic environment was significantly positively correlated with the changing rate of the climatic factors. The coupling relationship between the artificial ecosystem and external environmental factors was weak. The results of the negative feedbacks suggested a conservative coupling relationship between the vegetational natural ecosystems, forest, shrub, and grassland, and the external environmental changes, which had higher resilience than the non-vegetation ecosystems, like glacier, waters and wetland, bare land and desert. Therefore, protecting the natural vegetation in the area means to maintain the overall ecological barrier function of the Qinghai-Tibet Plateau.