柴达木东缘山地千年祁连圆柏年轮定年分析

Dating the1000-year-old Qilian J uniper in Mountains along the Eastern Margin of the Qaidam Basin

针对中国干旱区生长的树木缺失轮和伪轮多等具体情况,及常规树轮定年方法应用于中国干旱地区时所遇到的问题,本文以柴达木盆地东缘山地上生长的千年祁连圆柏树轮定年工作为例,详细探讨了在中国干旱地区建立树轮定年年表的方法体系及技术路线,对常规的工作方法提出新的改进。这包括:采样中要采集不同树龄、不同小生境且大复本量的样本;交叉定年工作要按一定的工作程序;安放缺失轮时要同时考虑窄轮和宽轮变化的一致性;用多种方法对定年和轮宽量测值进行检验等。这些方法的具体应用有助于在中国干旱地区建立定年准确、千年尺度的树轮年表。

In this paper, the methods for developing the master chr on ologies for 1000-year-old Qilian Juniper (Sabina przewalskii Kom.) are intr oduced in detail. Since the studied sites are located in the arid re gion of northeast Qinghai-Xizang Plateau, the tree-ring cores sampled c ontain a certain number of missing rings and several false rings. To assure the proper placement in time of each growth layer for the 100 0-year-old trees, some improvements were made in the practice of maste r chronologic development. Firstly, trees with a variety of ages were sampl ed besides very old trees. The large sample depth benefited the identification of missing rings for cores from old trees and avoided the possibility that all collected specimens could be missing a ring for any one year. Secondl y, cores from younger trees and from trees that exhibit a little width variation were selected to do the skeleton plot first and cores wit h many missing rings were done last when the ring-width pattern was known. Thirdly, inferring where rings may be missing was made based o n the agreement among the narrow rings as well as among the wide ri ngs. If the agreement of wide rings is not so good and there were some m issing rings, the chronology from nearby sites was used to infer the year of missing ring occurrence. Finally, several methods, such as the comput er program COFECHA and the line plots were used to examine the datin g and the measurements of ring width for a site. The number of core s without missing rings and time span covered by them were also inspected to avoid the possibility that all collected specimens were added a missing ring for any one year. The Gleichlaufigkeit statistics was used to ex amine the dating agreement between master chronologies of different sites.