海拔和树龄对树轮气候记录的影响研究

It is generally hypothesized that tree growth at the upper treeline is normally controlled by temperature while that at the lower tree line is precipitation limited. However, uniform patterns of inter-annual ring-width variations along altitudinal gradients are also observed in some situations. It is also generally considered that climate-growth relationships are age independent, once the biological growth trend and the influence of disturbance pulses have been removed. But the relationship between the tree ring and the climate changed with tree age has been found in some research area. Elevation and tree age have an impact on the tree-ring response to climate, which will affect the accuracy of the tree ring reconstruction of historical climate. Qilian Mountain is located in the intersection of the monsoon and westerly areas, which is sensitive to climate change, and there is a big elevation differences, and the forest was protected very well in this area, which provides a natural testing ground for studying the different altitudes different age groups tree-ring climate response relationship. This project propose to combined dendroecology and ecological field survey to investigate the effect of elevation and tree age influences on tree ring radial growth to climate change in the study area. Results of this study will lay the foundation for the tree-ring reconstructions of past climate, and it will provide scientific support for the forest how to response to the climate and forest protection with the global change.

树轮气候学研究中普遍认为森林上限树木的生长主要受温度的影响而下限树木的生长主要受降水的影响。然而，有些研究表明海拔高差不会引起限制树木径向生长的环境因子发生改变。经典的树轮年代学认为使用去趋势方法把不同树龄的样芯的年龄趋势去掉，但是这种方法会抹掉各年龄段树轮对气候变化响应的特征，有一定的局限性。海拔、树龄对树轮气候响应有所影响，这将影响树轮重建历史气候的精度。祁连山位于季风和西风的交汇区，对气候变化敏感，且该区山体海拔高差大，森林资源保护的较好，气候类型多样，为研究不同海拔、不同树龄树轮气候响应关系提供了天然试验场。因此，本项目拟通过野外调查和树轮生态学方法研究祁连山区不同海拔、不同树龄树木的径向生长特性及其对气候变化的响应特征，探究不同海拔、不同树龄树轮气候响应的普遍规律，为树轮气候学研究奠定基础，同时为该区森林对气候变化的响应研究和森林保护提供科学依据。

树轮-气候响应是进行古气候重建并进而分析气候变化规律的基础。有研究结果表明海拔、树龄对树轮气候响应有影响，这将影响树轮重建历史气候的精度。因此探究不同海拔、不同树龄树轮气候响应的普遍规律，为树轮气候学奠定基础，同时可为森林对气候变化响应以及森林保护提供科学依据。本项目选择不同海拔祁连圆柏、雪岭云杉和不同树龄油松、青杄、祁连圆柏为研究对象进行采样，研究结果表明海拔对树轮气候响应影响在不同的地区结果不一样，祁连山中部结果不同海拔树轮响应气候因子一致，只是存在响应显著程度的差异；天山的研究结果表明，高海拔树木的生长主要受低温的限制，而低海拔树木的生长主要受湿度的限制；不同树龄对气候变化响应基本一致，只是树龄较大的树木对水分响应更为敏感，表现为显著相关的月份更多，显著相关系数更高。另外，研究过程中发现，在祁连山东部高海拔发现小树死亡现象，研究发现，持续性干旱导致幼树死亡。研究结果将为研究区生态环境保护提供基础数据。