腾格里沙漠南缘哈思山树轮记录的NDVI变化

利用采自腾格里沙漠南缘哈思山的油松树轮样品建立树轮宽度年表，结合GIMMS归一化植被指数（NDVI）数据资料重建了本区1804~2009年6~9月NDVI变化序列。本研究分析了NDVI序列变化特征，在此基础上，探讨了本区植被变化与沙尘暴天气及其与干旱气候的关系，结果表明：近206年来腾格里沙漠南缘NDVI虽未发现显著增加趋势，但期间经历了多次波动；植被生长较好的阶段出现在1826~1829年、1849~1852年、1885~1895年、1934~1963年和1969~1978年，植被生长较差的阶段为1815~1823年、1831~1847年、1897~1909年、1924~1932年、1988~1993年和2001~2006年。发现NDVI极低值年份与周边地区沙尘暴多发期有良好的对应关系，说明腾格里沙漠南缘NDVI变化与当地沙尘天气有一定潜在联系，但地表植被变化对沙尘暴的发生起到的作用是有限的。腾格里沙漠南缘NDVI变化与旱涝等级及PDSI有显著的相关性，指示了水分条件对本区地表植被生长有明显的制约作用。

Variations of NDVI recorded by tree-ring in the Hasi Mountain,the southern margin of the Tengger Desert

The Normalized Difference Vegetation Index(NDVI)can reflect vegetation cover and the ecological environment change. In arid and semi-arid area, vegetation cover changes have an important influence on aeolian activities and desertification. Hasi Mountain(36°58.33'~37°02.67'N, 104°18.67'~104°35.00'E) located at the southern margin of the Tengger Desert, northwestern China, and it is an ideal area for study past climatic and environmental changes. Pinus tabulaeformis is the main tree species in this area. A total of 114 cores(1 to 2 cores per tree)were taken from 55 Pinus tabulaeformis trees in August of 2010. A tree-ring width chronology was developed based on tree ring data using the conventional method of dendrochronology. We analyzed the correlation relationship between tree-ring width chronology, climate and NDVI. The climate data(1957~2007)come from the Jingtai meteorological station(37°10.8'N, 104°03'E) and NDVI grid data(1981~2006)from the GIMMS(global inventory modeling and mapping studies), with spatial resolution of 0.22°×0.22° and temporal resolution of 15 days. The results indicated that climate of previous year played an important role in the radial growth of Pinus tabulaeformis. This chronology significantly and negatively correlated with temperature in autumn and winter. And it significantly and positively correlated with precipitation in previous September. This chronology significantly and positively correlated with NDVI from June to September, and has strongest correlation with NDVI in September with a correlation coefficient of 0.58. Therefore, we reconstructed the June~September NDVI time series from 1804 to 2009. This reconstruction accounts for 42.7% of the actual NDVI variance during the calibration period(1981~2006). The result from different calibration methods indicated that the NDVI reconstruction was reliable. On the basis of the analysis of temporal variation characteristics of NDVI, the responses of vegetation variations to sandstorm and arid climate occurred in this area were explored. The results showed that NDVI changes didn't have obvious increasing trend during this period in the southern margin of Tengger Desert, but NDVI values fluctuated many times. The growth of vegetation in this area were well in the periods of 1826~1829, 1849~1852, 1885~1895, 1895~1963 and 1969~1978, while it was worse in the periods of 1815~1823, 1831~1847, 1831~1909, 1924~1932, 1909~1993 and 2001~2006; The periods with lower NDVI values were consisted with the stages when sandstorm occurred frequently, suggesting that vegetation condition in the southern margin of Tengger Desert had certain connection with dust weather occurred locally, but the effect of vegetation changes on the occurrence of duststorm was limited; The reconstructed NDVI time series had significant correlations with the dryness/wetness index in Lanzhou and PDSI, indicating that the moisture conditions played a key role for the growth of vegetation in this area.