中国灌木生态系统的干旱化趋势及其对植被生长的影响

The study of shrubland drought dynamics in China and its impacts on vegetation growth

大量研究表明,21世纪全球气温将持续升高,干旱将不断加剧,具有超强抗旱能力的灌木在未来的区域乃至全球生态系统过程中将会发挥越来越重要的作用。灌木在我国有着广泛的分布,其总面积超过了我国陆地面积的20%。本研究旨在通过计算中国灌木生态系统的标准化降水蒸散指数(Standardized Precipitation Evapotranspiration Index, SPEI)来分析其干旱变化趋势及其对灌木生态系统植被生长的影响。结果显示,中国灌木生态系统的SPEI在1961—2013年间总体上呈显著地下降趋势,但其趋势在1992年发生了显著变化,这表明中国灌木生态系统正在持续地干旱化,并且在最近二十几年干旱化加剧。我们还分析了不同灌木生态系统EVI(Enhanced Vegetation Index, EVI)对SPEI变化的响应,结果显示不同的灌木生态系统类型对SPEI变化的响应不同。夏季,高寒荒漠灌木半灌木、温带荒漠灌木半灌木和温带落叶灌木EVI与SPEI变化显著正相关,而亚高山常绿灌木和亚热带常绿灌木EVI则与SPEI的变化显著负相关。温带落叶灌木EVI与春季SPEI变化显著正相关,但却与秋季和冬季的SPEI显著负相关。此外,亚热带常绿灌木EVI还与春季SPEI变化显著正相关。从空间上来看,北方的灌木生态系统比南方的灌木生态系统对干旱的变化更加敏感,同时,南方湿润地区的灌木在生态系统尺度也体现了较强的抗旱能力。在全球持续干旱化的大背景下,研究灌木生态系统EVI对干旱变化的响应将有助于对区域生态系统过程变化的理解。

Existing studies showed that a persistently increasing trend of aridity will dominate the global climate change in the future.Shrubs,which are widely distributed in China,with their excellent drought resistance and tolerance may play more important-roles in the global ecosystem function.In this study,we calculated a drought index(Standardized Precipitation Evapotranspiration Index,SPEI)to analyze shrubland drought dynamics in China from 1961 to 2013.We found that the SPEI of shrublands in China decreased significantly and the trend was significantly changed in 1992,indicating that shrublands in China experienced a persistent drought period that intensified in recent years.We also analyzed the effects of SPEI variation on EVI(Enhanced Vegetation Index,EVI),and found that different shrubland types responded differently to SPEI variation.Summer SPEI affected high-cold desert,temperate desert,and temperate deciduous EVI positively,but affected subalpine evergreen and subtropical evergreen EVI negatively.Temperate deciduous EVI responded positively to spring SPEI,but negatively to autumn and winter SPEI.Furthermore,subtropical evergreen EVI was also positively affected by autumn SPEI.In terms of location,the shrublands in Northern China were more sensitive to drought dynamics than shrublands in the South.Additionally,shrublands in the humid area of Southern China showed strong drought resistance.Learning the response of shrublands EVI to drought dynamics will contribute to the understanding of ecosystem process variation in the background of the global persistently increasing trend of aridity in the future.