祁连山中部地区树轮宽度年表特征随海拔高度的变化

利用采自祁连山中部地区不同海拔高度的四个采样点的青海云杉树轮样芯 ,分别建立了树木年轮宽度年表。发现随海拔高度的上升 ,树轮宽度指数的振幅减小 ,年表的平均敏感性降低 ,样本间的一致性也逐步减小 ,上限年表与气候因子的相关性最低 ,这与目前大家普遍认同的上限树木的生长受温度控制的概念并不一致。进一步的分析表明 ,年表的敏感性随海拔高度降低主要是由于该区域树木生长的限制因子是春季降水 ,而降水随海拔高度的升高而增加 ,从而使得春季降水对树木生长的限制作用随海拔升高而逐步减弱 ;生物学指标的测定结果表明 ,生长在高海拔的树木对环境的生态适应策略发生变化 ,其生理代谢维持在较低水平 ,以避免环境变化带来的影响 ,因此生长在高海拔的青海云杉对环境变化的敏感性较差。

Analysis of the tree-ring width chronology of Qilian Mountains at different elevation

Tree-ring cores taken from four sites at different elevations in the middle of the Qilian Mountains, in the arid and semi-arid region of northwestern China, were used to develop four tree-ring width chronologies respectively using standard dendrochronological methods. Three of these namely Heiwa, Tianlaochi and Meiyaokou, are located in Sidalong, a catchments of the Heihe River, in the Qilian Mountains, northwestern China. These three sampling sites lie very close to each other but at the different elevation. The fourth site, Xishui, is about 60 km from Sidalong. It is the lowest elevation site and also located in the catchment of the Heihe River in the Qilian Mountains. The tree ring cores were taken Picea crassifolia at the four different elevations. Results indicated that with increasing altitude the chronology fluctuation decreased. The statistical character of the chronology shows that mean sensitivity (M.S.) and standard deviation (S.D.) decreased with increasing elevation. In other words, the response of tree growth to environmental changes is decreased at higher elevation. The decrease of the correlation coefficients (R1, R2, and R3) indicates that the consistency of the tree's response to environment also decreases with altitude. The variance of the first eigenvalue (PC1) of each chronology also decreased with altitude, showing that the information contained in the tree ring chronologies decreased. Therefore, the sensitivity and the consistency of the tree's response to the environment changes decreased with increasing altitude.In order to understand the differing response of trees at different elevations to the environment changes, the correlation between the chronology indices and precipitation and between air temperature in different seasons were calculated. The results show that apart from the highest sample site at Meiyaokou, the indices of other three chronologies correlated to the spring precipitation significantly. The chronologies of Xishui and Tianlaochi showed negative correlation with summer air temperature with different level of significance. Only the chronology of the highest elevation site has no significant relationship with the meteorological data. The chronology of the low elevation site shows a stronger correlation with temperature rather than with precipitation.These results maybe due to that the restriction effect of the precipitation decreases with increasing elevation. Because the precipitation increases with the elevation in this area, the effect of precipitation on the growth of the trees becomes weak. However, air temperature is not a restriction factor. The measured results of the biological indices indicated that the stoma density and the dry weight of the spruce leaves decreased dramatically above about 3000m.a.s.l. This is response to a reducing in metabolism rate at high elevation, in order for the trees to avoid the effects of the harsh environment as much as possible. Hence, trees growing at high elevation show low sensitivity to the climate change in the study area. This conclusion is of fundamental important for the tree-ring research in arid and semi-arid area. It is important to understand the relationship between the climate change and the growth of the trees, in order to develop an appropriate ecological model of plant environmental reactions and hence to establish a valid basis on which to reconstruct long-term climate change in the past over a large scale.