祁连山东延余脉——兴隆山树木径向生长记录的公元1845年来夏季NDVI变化

NDVI能够反映地表覆盖和生态环境变化。在祁连山东延余脉采集树轮样本,分析树木径向生长与植被NDVI的相关关系,并重建历史时期植被NDVI变化。结果表明：树木径向生长与夏季NDVI受到水热条件变化的显著影响,且树轮宽度与夏季NDVI显著正相关,采用简单线性回归方法建立二者的拟合方程,方差解释量达0.600（R²_adj=0.582,F=34.472,P<0.0001）;公元1845年以来,重建的NDVI序列显示植被覆盖相对较低时期有19世纪60年代,80年代初期,20世纪初期和20-30年代,其中20世纪20-30年代NDVI低值期与中国北方大范围旱灾一致;重建的NDVI与旱涝指数显著负相关,证实重建NDVI序列的可靠,且显示该区旱涝演化趋势;周期分析表明公元1845年以来,NDVI序列存在2-3年、5年左右、13年左右和15年左右的振荡。

Summer NDVI variability recorded by tree radial growth in the Xinglong Mountain,the eastward extension of the Qilian Mountains,since 1845 AD

Normalized Difference Vegetation Index (NDVI) can reflect land cover and the ecological environment change. This study sampled tree-ring cores in the Xinglong Mountain -the eastward extension of the Qilian Mountains, analyzed the correlation relationship between tree radial growth and vegetation NDVI, and reconstructed NDVI variability. The results indicated that tree radial growth and summer NDVI were influenced significantly by hydrothermal condition in the study area, the tree-ring width correlated significantly and positively with summer NDVI, the fitted equation relating them was developed by using simple linear regression, and the explained variance of the reconstruction was 0.600 (R²_adj = 0.582, F = 34.472, P < 0.0001). The summer NDVI reconstruction since 1845 AD showed that vegetation coverage was relatively sparse in the 1860s, the early 1880s, the early 20th century and 1920s-30s, and the low period 1920s-30s corresponded to the megadrought that occurred widely in northern China. The NDVI reconstruction correlated significantly and negatively with the dryness/wetness index, which showed the reliability of the reconstructed NDVI and also some representation of the wet-dry evolution model. Cycle analysis showed that the NDVI sequence has presented 2-3 years, about 5 years, about 13 years and about 15 years of oscillation since 1845 AD.