Using satellite-observed Normalized Difference Vegetation Index （NDVI） dada and station-observed surface air temperature anomalies for the Northern Hemisphere （NH）, we analyze the spatio-temporal characteristics of vegetation variations in the Qinghai-Tibet Plateau and their correlations with global warming from 1982 to 2002. It is found that the late spring and early summer （May-June） are the months with the strongest responses of vegetation to global warming. Based on the Rotated Empirical Orthogonal Function （REOF） method, the study shows that the first REOF spatial pattern of average NDVI for May-June reveals the northern and southern zones with great inter-annual variations of vegetation, the northern zone from the eastern Ktmlun Mountains to the southwestern Qilian Mountain and southern zone from the northern edge of the Himalayas eastward to the Hengduan Mountains. The vegetation, especially grassland, in the two zones increases significantly with global warming, with a correlation coefficient of 0.71 between the first REOF of May-June vegetation and the April-May surface air temperature anomaly in the NH during 1982-2002. A long-term increasing trend in May-June vegetation for the plateau region as a whole is also attributed mainly to global warming although there are considerable regional differences. The areas with low NDVI （grassland and shrubland） usually respond more evidently to global warming, especially since the 1990s, than those with moderate or high NDVI values.
The relationship between the carbon isotopic composition of paleosols and paleovegetation on the Loess Plateau is still unclear. One of the main reasons is that we are short of knowledge about the characteristics of the carbon isotopic composition of modern soil in this area. A preliminary investigation of the carbon isotopic compositions of the modern soil and the loess/paleosol sequence on the Loess Plateau shows that the carbon isotopic composition of modern soil is consistent with the distribution of modern plants on the Loess Plateau, where the ecosystem is dominated by a mixture of C4 and C3 plants. Comparing theδ13C values of modern soil and loess-paleosol sequences from the Xunyi profile, we conclude that C3 plants dominated the landscape during loess sediment stages, while C4 plants expanded during paleosol stages.
LIU Weiguo NING Youfeng AN Zhisheng WU Zhenghai LU Huayu CAO Yunning
Using wet digested method and ICP mass spectrometer, we analyzed the concentration of five trace elements (Cd, Mn, P, Zn and Pb) for the tree rings from both urban and suburbs of Xi'an. At the urban sampling site, one Chinese mahogany (Toona sinensis) disc and one phoenix tree (Firmiana simplex) disc were sampled from a steelworks in Xi'an City. At the suburb site, a Chinese mahogany disc was collected from a village in the south of the City. In addition, some soils near the roots of the sampled trees were collected. The analysis results indicate that the concentration of each of the five elements in annual rings has a positive correlation with the production of the steelworks. Statistical calculations show that Pb and Mn elements were stable without lag effects. That means these two elements do not move between rings. Cd displayed one year moving, P two years and Zn three years. These results are quite similar to those found by other methods.
LIU YuTA WeiYuanBAO TingYiYANG ZengYueSONG HuiMingLIU NaWANG WeiPingZHANG HongYiZHANG WeiAN ZhiSheng
Three well-dated Sabina Przewalskii ring-width chronologies from Dulan, China, have been used to reconstruct annual precipitation (from prior July to current June) variations on the northeast Tibetan Plateau since 850 AD. The reconstructions account of the instrumentally recorded precipitation variance are: 54.7% for the period of 1385-2000AD; 50.5% for 1099-1384AD and 45.7% for 850-1098AD. On the millenary scale, the precipitation variation over this region displays “W” shape, which has three peaks and two valleys. The precipitation is low during 1571-1879 AD, and high during 1880-2000 AD. 1900-2000 AD is the century with the highest precipitation over the northeast Tibetan Plateau in the last 1000 years, and 1962-2000 is the period with the highest pre- cipitation, and the highest variability of precipitation as well in the last 1000 years. The reconstructed series also reveals that the variability of annual precipitation is large when the precipitation is more, and contrarily, variability is small when the precipitation is low. With the temperature increasing obvi- ously in the 20th century, the precipitation in the study region significantly increased too, the variability of precipitation became larger, and drought and flooding occurred more frequently. The yearly tree-ring width (high frequency signal) series in this region reflects the local annually precipitation variation. However, the series with 40-year moving average (low frequency signal) cor- responds to the Northern Hemisphere temperature variations on the decadal to centurial scale. It correlates significantly with seven temperature curves of the Northern Hemisphere in the different time spans. For example, the correlation coefficients with the most temperature curves are around 0.9 during the period of 1852-1982 AD. In general, the temperature and the precipitation change syn- chronously in the Dulan region. It means that low temperature corresponds to low precipitation, andvice versa. This relationship may indicate that the climatic pattern i
