1982-2018年中国植被覆盖变化非线性趋势及其格局分析

探究植被覆盖变化是评估陆地生态系统环境变化的重要手段，但现有研究多采用线性趋势来表达植被覆盖的变化情况而忽略了趋势的非线性。本文使用GLASS FVC数据，利用BFAST方法和格局分析，探讨了1982-2018年我国植被覆盖变化的非线性趋势及其分布格局。结果表明：（1）与线性趋势方法的对比发现，BFAST的检测结果揭示了四川盆地、黄土高原等地的植被覆盖显著增加趋势其实存在中断，青海和东北等地植被覆盖经历了由退化到改善的过程而并非简单的线性增加，而青藏高原中东部等地则由原先的改善趋势变为了退化趋势。（2）将非线性趋势结果进行分类，其中单调型增加类型占比最多，达到33.58%，主要分布在内蒙古、陕西及河南等地；单调型减少占比1.82%，主要分布在东南沿海地区；中断型增加占比22.91%，主要分布在四川盆地东部和华北地区；中断型减少占比2.68%，主要分布在青藏高原东南部；由增到减占比4.20%，主要分布在青海等地；由减到增占比14.62%，主要分布在吉林等地。大范围的植被覆盖增加趋势充分反映了我国过去几十年植被的改善，但同时存在的减少趋势表明潜在的植被退化风险仍不可忽视。（3）不同趋势类型发生改变的时间有所差异，总体上1988-1999年间发生的改变较少，而2000-2011年间发生的改变较多，我国21世纪以来实施的大规模生态保护和恢复工程对植被的改善过程有重要影响。（4）分布格局上，植被覆盖改善趋势类型（单调型增加，中断型增加，由减到增）呈现大聚集，小分散的特点，具有复杂的形状；退化趋势类型（单调型减少，中断型减少，由增到减）的面积均较小，分布也相对离散。全国尺度上趋势空间格局呈现一定规律但分布的异质性较大，区域尺度上植被覆盖经受的干扰显著，变化过程实际也是较为复杂的。本研究表明，使用非线性趋势方法和格局分析，可以更准确地评估植被覆盖的时空变化，从而为生态环境相关工作的开展提供科学的参考。

Nonlinear trends and spatial pattern analysis of vegetation cover change in China from 1982 to 2018

The study of vegetation cover change is an important tool to evaluate the change of terrestrial ecosystem, but the previous studies mostly used linear trend to express the change of vegetation cover, ignoring the change of trend over time. Using GLASS FVC data, BFAST method and landscape pattern analysis, the nonlinear trend and distribution pattern of vegetation cover change in China were explored from 1982 to 2018. The results showed that:(1) compared with the results of linear trend method, although the vegetation cover in Sichuan Basin and the Loess Plateau presented a significantly linear increase trend, the detection results of BFAST showed that the increase trend was interrupted. Meanwhile, in Qinghai and Northeast China, the vegetation cover experienced a shift from degradation to improvement rather than simple linear increase, while it changed from the first improvement trend to later degradation in the middle east of Qinghai-Tibet Plateau. (2) Among the nonlinear trend types, the monotonic increase trend accounted for 33.58%, mainly distributed in the Inner Mongolia, Shaanxi, Henan and other places; the monotonic decrease trend accounted for 1.82%, mainly distributed in the southeast coastal area; the interrupted increase trend accounted for 22.91%, mainly distributed in the east of Sichuan Basin and the North China; the interrupted decrease trend accounted for 2.68%, mainly distributed in the southeast of Qinghai Tibet Plateau; the trend shifted from increase to decrease type accounted for 4.20%, mainly distributed in Qinghai; the trend shifted from the decrease to increase type accounted for 14.62%, mainly distributed in Jilin. The large-scale increasing trend of vegetation cover fully reflected the improvement of vegetation in China during the past few decades, but the monotonic decrease and the increase to decrease trends showed that the potential risk of vegetation degradation could not be ignored. (3) The time of change of different trend types were different, less occurred from 1988 to 1999, but mainly occurred from 2000 to 2011, which has been probably affected by the large-scale ecological protection and restoration projects since the 21st century. (4) The patches of the vegetation improvement trend type (monotonic increase, interrupted increase, decrease to increase) were characterized by large aggregation, small dispersion, and complex shape driven by strong interference, indicating that the process of vegetation cover change was actually very complex with high diversity on the regional scale; the patches of degradation trend type were small and dispersedly distributed. This study shows that the nonlinear trend and pattern analysis can more accurately evaluate vegetation cover change, so as to provide a scientific reference for the protection and recovery of ecological environment.