芦芽山阳坡不同海拔华北落叶松径向生长对气候变化的响应

为研究树木生长对气候变化的响应状况,选取芦芽山阳坡的3个海拔高度建立了华北落叶松(Larix principis-rupprechtii)的树轮宽度年表。年表的统计参数表明,3条年表均为研究气候信息的可靠资料。结果表明,芦芽山阳坡华北落叶松的径向生长和生长与气候的关系均具有海拔差异,中海拔(2440 m)和高海拔(2540 m)的华北落叶松具有相似年际生长变化,而二者均与低海拔(2330 m)华北落叶松的年际生长不同。低海拔华北落叶松的生长与4月平均气温和上一年11月降水量显著负相关,而中海拔和高海拔的生长均与上一年10月平均气温和6月降水量显著负相关。通过年表与气候因子之间的滑动相关分析发现,3个海拔高度华北落叶松生长与气候因子的关系均不稳定,生长与气温条件之间的显著相关关系是随着气温升高而出现的。气温的升高引起了华北落叶松生长与气温因子关系的海拔差异,以及径向生长的海拔差异。这一结果对于气候变化对植被垂直梯度影响的研究具有一定参考价值。

Responses of radial growth in Larix principis-rupprechtii to climate change along an elevation gradient on the southern slope of Luya Mountain

Many studies have addressed the effects of climatic factors on the radial growth of trees in different habitats. However, changes in climate can modify the relationships between tree growth and climate, and this, in turn, can modify the annual growth patterns of trees. Luya Mountain, located in the north of central China, has experienced a clear increase in air temperature over the last several decades according to the findings of the Intergovernmental Panel on Climate Change. The Wuzhai County Meteorology Station has also recorded an increasing trend in the annual mean air temperature and a slight decrease in total annual precipitation from 1996 to 2007. Trees at three different elevations on the southern slopes of Luya Mountain (low, 2330 m;middle, 2440 m;and high, 2540 m) were selected for study, and tree-ring chronologies were created to study variation in radial growth response of Larix principis-rupprechtii trees to climate change along an elevation gradient. A total of 92 cores from 46 trees were collected, and ultimately three residual chronologies were created, one for each of the three elevations. Statistical analysis of the chronologies revealed the expressed population signals of all three chronologies exceeded 0.85, the minimum threshold indicating a strong climatic signal in tree ring chronologies. This implies that the three chronologies were all suitable for growth-climate relationship studies. Pearson''s correlations were calculated between the tree-ring chronologies and monthly climatic factors (monthly means of temperature, maximum temperature, and minimum temperature as well as total monthly precipitation) to investigate the climatic responses of trees. Moving correlation analysis was also applied to the tree-ring data and these monthly climatic factors. This allowed further analysis of the stability of the relationships between each pair of chronologies, and the relationships between tree growth and climate. The annual growth rhythms of Larix principis-rupprechtii and their relationships with climatic factors varied over time and among the three elevations. Similar annual growth rhythms were found at the mid-elevation (2440 m) and high elevation sites (2540 m), but these differed from those of trees at the low elevation site (2330 m). As for the relationship between tree growth and climate, growth at low elevation showed significant negative correlations with both monthly mean temperature in April and total monthly precipitation in the previous November, whereas the trees at middle and high elevations exhibited significant negative correlations with monthly mean temperature in the previous October and total monthly precipitation in June. However, none of these relationships between tree growth and climatic factors at the three elevations were stable based on the moving correlation analysis. The correlations between tree growth and the main climatic factors became significant in 1996, when the annual mean air temperature showed an abrupt increase. Similarly, the elevational variation in the relationships between tree growth and climate, as well as in the growth rhythms, both of which also are first apparent in 1996, suggest climatic warming drives elevational variation in growth-climate relationships and growth rhythms. The findings of this study build on our knowledge of elevational variation in the influence of climate change on vegetation.