黄河源植被覆盖度变化及空间分布自然驱动力分析

Analysis of Vegetation Coverage Changes and Natural Driving Forces of Spatial Distribution in the Source Region of the Yellow River

归一化植被指数(NDVI)可以有效地反映地表植被的生长状况,研究植被NDVI空间分布的驱动因素有助于区域生态环境保护。该研究基于2000—2018年黄河源区MODIS-NDVI数据和同时期8种自然因子数据,运用趋势分析法分析黄河源区植被NDVI时空变化特征,并利用地理探测器分析其空间分布的自然驱动因子。研究表明,黄河源区植被覆盖总体较高,2018年区域内74%的面积NDVI大于0.6。NDVI分布特点为东南高西北低,变化格局为北部增加,中部减少。2000—2018年NDVI均值总体上呈增加趋势,但变化趋势不明显,增长率为0.013/10 a;除高植被覆盖区面积增加外,其他等级植被覆盖区面积均减小。年降水量对NDVI空间分布的影响力最大,达到0.602;高程影响力为0.385,年均温影响力为0.296,也很好地解释了黄河源区的植被覆盖状况;其他自然因子对NDVI空间分布的影响力较小。自然因子对植被NDVI的影响呈现相互增强和非线性增强关系,使地貌类型、坡度及坡向等影响较小的单因子对植被NDVI也有了较大的影响,其中,年降水量与其他因子之间的交互作用的影响力普遍较高,年降水量与海拔的交互作用影响力最大,达到0.682。研究表明,2000—2018年黄河源植被覆盖度呈不显著增加,年降水量是影响植被NDVI空间分布的主导因子,自然因子对植被NDVI的影响具有交互作用。该研究有助于更好地认识黄河源区植被覆盖情况以及植被空间分布的影响机制。

The normalized difference vegetation index(NDVI)can effectively reflect the growth of surface vegetation.Studying the driving factors of the spatial distribution of the NDVI is helpful for regional ecological environment protection.Based on the MODIS–NDVI data and the data of eight natural factors in the source region of the Yellow River during 2000–2018,this study used trend analyses to examine the temporal and spatial variation characteristics of the NDVI in the source region of the Yellow River.The spatial heterogeneity and natural driving factors were analyzed by geographical detectors.The study showed that the overall vegetation coverage in the source region of the Yellow River was high.In 2018,the NDVI of 74%of the area was greater than 0.6.The NDVI was comparatively high in the southeast and low in the northwest,and showed an increase in the north and a decrease in the middle.The mean NDVI value had generally increased during 2000–2018,although the trend was not obvious,and the growth rate was 0.013/10 a.Except for the increase in the area of high vegetation coverage,the area of other grades of vegetation coverage decreased.The influence of annual precipitation on the spatial distribution of NDVI was the largest,reaching 0.602.In addition,the influence of elevation was 0.385 and the influence of average annual temperature was 0.296,reflecting the vegetation coverage condition in the source region of the Yellow River.The influence of other natural factors was comparatively smaller.The influence of natural factors on vegetation NDVI showed bivariate enhancement and nonlinear enhancement relationships,so that single factors with smaller impact,such as landform type,slope,and aspect,also had a great influence on vegetation NDVI.The influence of the interaction between annual precipitation and other factors was generally high.In particular,the influence of the interaction between annual precipitation and elevation was the greatest,reaching 0.682.This study showed that the vegetation coverage of the source region of the Yellow River had not increased significantly during 2000–2018.The annual precipitation was a dominant factor affecting the spatial distribution of the NDVI,and the influence of natural factors on vegetation NDVI was interactive.This study contributes to a better understanding of the vegetation coverage in the source region of the Yellow River and the influencing mechanism of vegetation growth.