长江流域生态系统恢复力评价及其空间异质性研究

恢复力是生态系统的固有特征，可通过系统遭受干扰后恢复到原稳定态的时间和速率来衡量. 开展长江流域生态系统恢复力研究对于掌握流域生态系统变化规律，指导长江流域大保护和高质量发展具有重要意义. 本文采用概率衰减法评估长江流域生态系统恢复力，首先获取了2001—2020年长江流域每16 d的250 m分辨率的增强型植被指数(enhanced vegetation index, EVI)数据，采用最大值合成以及重采样技术，获得年度1 000 m分辨率的EVI数据；然后，计算每个栅格2001—2010年、2001—2011年、2001—2012年直至2001—2020年共11年的EVI变化斜率；以全流域为统计单元，统计11年间EVI变化斜率持续为正和持续为负的栅格数量，采用衰减函数进行拟合，正负衰减的时间差表征生态系统恢复力；以6 767个小流域为对象，分析长江流域生态系统恢复力的空间差异性. 结果表明:20年来长江流域整体EVI在逐渐增加，空间分布差异在逐渐增大. 正、负衰减时间差为29.48 a，生态系统处于正向恢复状态. 生态系统恢复力呈上游及下游入海口低、中游地区高的特点，其与降雨量、地形(海拔和坡度)、林草覆盖率和人类活动等因素相关. 在海拔1 000~1 500 m、坡度25°~30°、林草覆盖率较大的山地区域生态系统恢复力最高；而在高海拔或低海拔地区以及植被覆盖较差的地区，生态系统一旦受到干扰或破坏则较难恢复. 研究显示:长江流域生态系统整体上呈正向演替，得益于长江大保护的政策；长三角地区因人类活动频繁，生态处于逆向演替，而上游地区如金沙江、大渡河、岷江一带生态系统恢复力较低，与水电开发、地质灾害是否相关需进一步研究. 

Assessment and Spatial Heterogeneity of Ecological Resilience in the Yangtze River Basin

Resilience is an inherent characteristic of ecosystems and can be measured by the time and rate at which the system returns to its original stable state after disturbance. It is of great significance to study the ecosystem resilience of the Yangtze River Basin for grasping the laws of ecosystem changes and guiding the protection and high-quality development of the Yangtze River Basin. In this paper, the probability attenuation method was used to assess the ecosystem resilience of the Yangtze River Basin. Firstly, the enhanced vegetation index (EVI) data with a 250 m resolution every 16 d in the whole basin from 2001 to 2020 were obtained, and the annual EVI data with 1000 m resolution were obtained by maximum synthesis and resampling technology. Then the slope of the EVI change for each grid was calculated for 11 years from 2001 to 2010, 2001 to 2011, 2001 to 2012 and 2001 to 2020. Taking the entire watershed as the statistical unit, the number of grids with continuous positive and continuous negative slopes in 11 years was counted, and the decay function was used to fit, and the time difference between positive and negative decay was used to represent the resilience of the ecosystem. The spatial differences of ecosystem resilience in the Yangtze River Basin were studied in 6767 small river basins. The results showed that the overall EVI in the Yangtze River Basin increased gradually in the past 20 years, and the spatial distribution difference has gradually increased. The time difference between positive and negative decay was 29.48 years, indicating that the ecosystem was in a positive recovery. The ecosystem resilience was lower in the upstream and downstream estuary and higher in the middle reaches, which was related to rainfall, topography (altitude and slope), forest and grass coverage, human activities and other factors. The ecosystem resilience was the highest in the mountain region with a slope of 25°-30° and high vegetation coverage at an altitude of 1000-1500 m. However, in high-altitude and low altitude areas with poor vegetation coverage, ecosystems are difficult to recover once it is disturbed or damaged. The research shows that the overall ecosystem of the Yangtze River basin is in a positive succession, thanks to the national policy of Yangtze River conservation. Due to frequent human activities, the ecology of the Yangtze River Delta is in reverse succession, while the ecosystem resilience of the upstream regions, such as Jinsha River, Dadu River and Minjiang River, is low, and whether it is related to hydropower development and geological disasters needs further study.