黄土高原不同植被覆被类型NDVI对气候变化的响应

植被与气候是目前研究生态与环境的重要内容。为探究黄土高原地区植被与气候因子之间的响应机制,利用线性趋势分析、Pearson相关分析、多元线性回归模型以及通径分析的方法,对黄土高原2000—2015年全区和不同植被覆被类型区内NDVI与气候因子的变化趋势以及相互作用关系进行分析。植被覆被分类数据和植被指数数据分别来源于ESA CCI-LC(The European Space Agency Climate Change Initiative Land Cover)以及MODND1T/NDVI(Normalized Difference Vegetation Index)。结果表明:(1) 2000—2015年黄土高原全区植被年NDVI_(max)显著增加的区域占总面积的74.25%,不同植被覆被类型年NDVI_(max)分别为常绿阔叶林常绿针叶林落叶阔叶林落叶针叶林镶嵌草地农田镶嵌林地草地灌木,并且都呈显著增加趋势,其中常绿阔叶林和农田增加幅度最大,为0.012/a。(2)黄土高原全区NDVI与气温、日照、降水和相对湿度等气候因子之间没有显著相关性,但在不同植被覆被类型区,气候因子对NDVI存在显著作用,且不同植被覆被类型差异明显。(3)在全区和不同植被覆被类型区NDVI仅对降水的响应比较一致,气温无论在整个区域尺度还是不同植被覆被类型区对植被的影响均不显著。(4)常绿阔叶林、落叶阔叶林、常绿针叶林及镶嵌林地等以乔木为主的植被覆被类型受年均相对湿度和年总日照时数的显著负效应驱动,草地、镶嵌草地等以草本为主的植被覆被类型则受到年总降水量的显著正效应影响。这说明对植被类型进行区分,更有利于揭示气候对植被的作用机制。

Normalized difference vegetation index of different vegetation cover types and its responses to climate change in the Loess Plateau

Vegetation and climate are important aspects of ecology and environmental research. To explore the relationship between vegetation and climatic factors in the Loess Plateau, we analyzed the trends and responses of vegetation to climate changes in the whole zone as well as in different types of vegetation cover zones using linear trend analysis, Pearson''s correlation analysis, multiple linear regression models, and path analysis methods published between 2000 and 2015. The vegetation cover classification data were obtained from maps published by European Space Agency Climate Change Initiative Land Cover (ESA CCI-LC) and the Normalized Difference Vegetation Index (NDVI) data were derived from MODND1T/NDVI vegetation index data. The results indicated that (1) from 2000 to 2015, the regions with significant increase in NDVI_max in the Loess Plateau accounted for 74.25% of the total area, and among all the different vegetation cover types, the evergreen broad leaf forests and crop showed the greatest increase of 0.012/a. The decreasing order of the means of NDVI_max of the different vegetation cover types is as follows:evergreen broad leaf forests > evergreen needle leaf forests > deciduous broad leaf forests > deciduous needle leaf forests > mosaic grassland > crop > mosaic tree > grassland > shrub; (2) there was no significant correlation between NDVI and climatic factors such as temperature, sunshine hours, precipitation, and relative humidity in the whole zone. However, in different vegetation cover type zones, climatic factors had different significant effects on NDVI; (3) NDVI in the whole zone and in different vegetation cover type zones changed consistently with change in precipitation, whereas change in temperature did not have a significant effect; (4) vegetation cover types that were dominated by trees, such as forests with evergreen broad leaves, deciduous broad leaves, evergreen needle leaves and mosaic trees, were significantly affected by the mean annual relative humidity and mean annual sunshine hours. However, grass-dominated vegetation types, such as grasslands and mosaic grasslands, were significantly affected by the total annual precipitation. These results imply that the distinction between vegetation types is more important in studying the impact of climate change on vegetation.