近百年来全球气候正经历一次以变暖为主要特征的显著变化,但不同的生态系统对全球变暖如何响应是一个值得深入研究的问题。本研究选取阿尼玛卿山区三个坡面(YYC\HBS\HHB)以及林线处的祁连圆柏,利用树轮生态学方法来研究树木更新以及林线动态与气候变化之间的关系。通过对三个坡面以及各坡面的上限圆柏的年龄结构以及林线动态分析发现:自14世纪末期开始,YYC坡面树木便处于不断的更新之中;15世纪末期以来HBS坡面树木开始更新;HHB坡面从18世纪末期开始才有树木更新;YYC坡面树木更新出现了1550-1650年和1800-1900年两个高峰期;HBS坡面和HHB坡面的树木更新只有1800—1900年一个高峰期;三个坡面上限圆柏的更新都只有一个高峰期:1800—1900年。近百年没有显著的更新是由于没有采集小树,因此本文没有讨论近百年的树木更新。树木平均年龄随着海拔的升高而不断减小,表明近200年来树木的更新和林线向高海拔迁移在本研究区体现很明显。树木年龄更新变化通过与重建的中国温度(Yang et al,2002)和北半球温度(D'Arrigo et al,2006)对比发现,阿尼玛卿山树木更新变化与升温关系密切,这表明温度可能是研究区树木更新的一个决定因素。
This paper presents a 457-year reconstruction of precipitation in the southeastern Qinghai-Tibet Plateau using tree-ring records.Tree-ring samples were collected from the Hengduan Mountains in the southeastern part of the Qinghai-Tibet Plateau,China.A nearly 500-year chronology was developed using tree-ring width records.Correlation analysis shows moisture is the main factor limiting tree growth in this region.Ring-widths were significantly positively correlated with the Palmer Drought Severity Index(PDSI) and precipitation in many months.The highest correlation coefficient was found between the annual growth of trees and precipitation from the previous September to the current June(0.738).Based on this relationship,we reconstructed the precipitation history from 1509 to 2006.The reconstruction explains 54.4%(Radj2=53.5%,N=49,F=56.12) of the actual precipitation variation during the calibration period(1958-2006).During the reliable period of the reconstruction(1549-2006),some low-frequency climate signals are included,indicating this region has been getting wetter in the last 20 years.The reconstruction documents six apparently dry and five pluvial periods and the 17th century dry period lasted longer than any other.When compared with other recent studies,this study and these earlier reconstructions show a similar trend in the variation of drought and pluvial.Further spatial correlation analysis confirms that the reconstructed precipitation adequately represents the rainfall history of the entire Hengduan Mountain area.The Multi-taper method,a type of spectral analysis,reveals that precipitation in this area had significant(P<0.01) spectral peaks at 3-5 a,60 a and 79-85 a.
