丝绸之路青海道吐蕃时期墓葬出土木材记载的森林干扰史

森林动态与气候变化及人类活动有着紧密的联系, 了解森林干扰的发生历史对准确预测全球变暖背景下的森林动态具有重要意义, 也可为理解历史时期的气候变化和人地关系演变提供线索。文章利用丝绸之路青海道沿线吐蕃时期3个墓葬中出土的78棵祁连圆柏(Juniperus przewalskii Komarov)原木作为研究对象, 利用树木年轮学方法分析了其干扰历史。结果表明: 在公元1世纪到公元8世纪, 该地区祁连圆柏个体平均出现了51个主要生长释放事件年与15个主要生长抑制事件年, 其中公元4世纪下半叶的干扰事件发生频率最高。在公共区间85~700 A.D. 期间, 该地区森林出现大范围生长抑制事件的主要时期为537~548 A.D., 大范围生长释放事件发生在372~393 A.D. 和561~574 A.D. 期间。墓葬周边现生祁连圆柏生长与气候因素的响应分析以及相关的历史资料显示, 气候条件由干转湿是导致该地区森林生长释放事件的重要原因, 吐谷浑与吐蕃到达柴达木地区后增加的森林采伐与森林破坏也可能促进了生长释放的发生。研究结果有助于进一步认识青藏高原东北部历史时期森林干扰的发生规律, 以及气候变化和人类活动对丝绸之路青海道沿线森林产生的影响。

HISTORY OF FOREST DISTURBANCES RECORDED BY TIMBERS UNEARTHED FROM TUBO TOMBS ALONGSIDE THE SILK ROAD'S QINGHAI ROUTES

Forest dynamics is closely associated with climate change and human activities, understanding the history of forest disturbances is of great significance for predicting forest dynamics under the background of global warming, it can also help to understand climate change and human-environment interactions in historical times. However, due to the absence of precise records and the presence of cascading effects resulting from climate-human feedbacks, unravelling forest dynamics is challenging since the impacts of climatic and anthropogenic drivers are hard to distinguish. In this study, we utilized dendrochronological methods to study growth release and suppression events of trees in order to reconstruct the disturbance history of forests. A total of 177 tree-ring samples were collected from 78 juniper timbers(Juniperus przewalskii Komarov) unearthed from three Tubo tombs(ZGR: 36.24°N, 98.15°E; MKL: 35.86°N, 97.99°E; RS: 36.16°N, 98.31°E) alongside the Silk Road's Qinghai Routes in Dulan County(on the east edge of the Qaidam Basin, northeast of Qinghai-Tibetan Plateau). To further understand the driving factors of forest disturbances, a correlation analysis was performed for the meteorological records(Dulan Meteorological Station: 36.18°N, 98.06°E) and tree-ring width chronologies(LL: 36.17°N, 98.42°E; QLG: 36.03°N, 98.20°E) collected from living Qilian junipers nearby the three tombs. Percentage of growth change(GC%) was calculated to identify the disturbance events, major growth releases were defined as an median GC% (ten years) of more than 50%, while major growth suppressions were defined as an median GC% (ten years) of less than -50%. The results indicated that trees in this region had an average of 51 major growth releases and 15 major suppressions from the 1st century A.D. to the 8th century A.D., disturbance events occurred most frequently in the second half of the 4th century. Synchronous growth suppression occurred in 537 A.D. to 548 A.D., while synchronous growth releases occurred in 372 A.D. to 393 A.D. and 561 A.D. to 574 A.D. To further understand the driving factors of forest disturbances, a correlation analysis was performed for the meteorological records and tree-ring width chronologies collected from living Qilian junipers nearby the three tombs. We found that tree growth was significantly and positively correlated with mean May-July PDSI and May-June precipitation, and negatively correlated with June temperature in this region, suggested that disturbances caused by the variation of moisture content might be the main reason for the release of regional forest. There were also unsynchronous growth releases and suppressions at three ancient wood sampling sites, which suggest canopy gaps caused by human activities alongside the Silk Road's Qinghai Routes may be another reason for forest disturbances, the increase in human disturbance after the arrival of Tuyuhun and Tubo in the Qaidam Basin might also promote the occurrence of growth releases. Our findings are helpful to further understand the occurrence of forest disturbance in the historical period of the northeastern Qinghai-Tibetan Plateau and its relationship with climate change and human activities.