太白山南北坡高山林线太白红杉对气候变化的响应差异

气候变化对秦岭植被生长的影响已经引起了人们的广泛关注,在相同的立地条件下,植被对气候变化的响应会因坡向不同而产生差异,秦岭的分水岭太白山尤为典型,为更进一步揭示不同坡向太白红杉(Larix chinensis)对气候变化响应的差异,以树木年代学为依据,利用采自太白山南、北坡相同海拔的太白红杉树芯样本分别建立了树轮年表,并分析了两者的年表特征,探讨了树轮宽度指数与气候因子之间的相关性及逐步线性回归方程。结果表明:太白山南、北坡太白红杉年表的平均敏感度、样本间平均相关系数、样本总体代表性等特征值较高,表明两个不同坡向年表中皆含有丰富的环境信息,相对而言,北坡样地植被对气候的响应较南坡样地敏感;由相关性分析可知,南北坡太白红杉差值年表对气温和降水响应显著的月份有所差异,北坡样地轮宽指数与当年和前一年1—6月平均气温皆为显著正相关关系,而南坡样地轮宽指数仅与当年5—6月平均气温通过显著性检验。南、北坡太白红杉径向生长都明显受到前一年6月降水"滞后效应"的一致影响,但北坡仅与当年8月的降水呈显著正相关,南坡与当年1—4月的平均降水量存在十分显著的负相关;多元线性逐步回归模型显示,气温因子对回归方程的贡献最大值均大于降水因子的贡献最大值,表明气温因子的变化更易引起太白红杉树轮宽度的变化,另外,气温因子对北坡样地回归模型的贡献值比气温因子对南坡样地回归模型的贡献值大,表明北坡样地处树轮宽度指数对气温因子更敏感,并且与相关分析结果一致。

Differences in growth response of Larix chinensis to climate change at the upper timberline of southern and northern slopes of Mt. Taibai in central Qinling Mountains, China

The impact of climate change on the plant growth has gained attentions, especially for those boreal trees growing at the timberline area. Topographical character such as slope aspect may affect the response of plants growth to climate even if with the same stand condition. This is especially significant between southern and northern slopes of Mt. Taibai, the main geographical watershed of Qinling Mountains. In this study, the chronologies were established by exploiting Larix chinensis tree-ring samples that collected from both northern and southern slopes of Mt. Taibai with a similar elevation of 3100-3200 meters. The characteristics of the chronologies were compared and the correlations between tree ring width indices and climatic factors were analyzed for both slopes of Mt. Taibai, respectively. The mean sensitivity, sample inter-correlation coefficients, overall sample representative and other values of the chronology characteristics are all very high, indicating that the tree-ring samples collected from both slopes of Mt. Taibai contained enough environmental information, and the plants at the timberlines were more sensitive to climate change on the northern than on the southern slope. According to the correlation analysis, radial growth of the Larix chinensis in different slopes were mainly affected by different aspects of the climatic factors from different months. Residual chronology was correlated positively with mean air temperature during January to June on the northern slope, while only with that during May to June on the southern slope. The Larix chinensis'' growth on both northern and southern slopes were correlated positively with the precipitation occurred in June of the previous year. However, the tree-ring width indices had a significant positive correlation with precipitation occurred in August of current year on the northern slope,while had a significant negative correlation with the mean precipitation from January to April of current year on the southern slope. The multi-variant liner step-wise regression modeling showed that the maximum contribution values of the air temperature factor in both regression functions are greater than that of the maximum value of attribution from precipitation, indicating that the change in tree-ring width of Larix chinensis was due to the variations in temperature than in precipitation in Mt.Taibai. Moreover, the tree-ring width residual chronology was more sensitive to temperature on the northern slope than on the southern slope since the temperature contribution to the function on the northern slope was higher than that on the southern slope which is also confirmed by the correlation analysis between the residual chronologies and the climate factors.