牛背梁自然保护区林线不同海拔巴山冷杉径向生长对气候变化的响应

近年来气候变化对秦岭植被的影响已得到众多研究的证实，牛背梁作为秦岭东部主脊和国家级自然保护区，该地区亚高山林线植被对气候变化的生态响应现状尚未得到广泛关注。依照树木年代学原理，进行响应分析并建立回归模型，探讨了牛背梁林线关键树种巴山冷杉（Abies fargesii）年表特征及对气候响应的海拔分异特征。结果表明：（1）随海拔升高，树木生长对气候的敏感性逐渐上升，但轮宽年表的同步性和信号强度呈先下降后上升的特点。（2）不同海拔树轮宽度年表的气候响应结果基本一致，对气温的敏感性均较降水强，敏感时段为当年2～8月，差异主要体现在，高海拔树木受生长季末期8月气温的影响较重，中海拔树木受生长季前期3～4月降水和上年冬季10～11月气温的促进，而低海拔树木受初春1～2月降水的限制作用明显。（3）对比分析低、中、高海拔3个回归模型中显著因子的变化趋势，发现气候变化可以促进巴山冷杉生长季的提前，但不同海拔树木的生长动态各异，说明研究区林线不同海拔巴山冷杉生长对全球变化可能具有不同的响应机制。

Radial growth response of Abies fargesii to climate change from different elevations at timberline of Niubeiliang Natural Reserve

Qinling Mountains is a major east-west mountain range in southern Shaanxi Province which provides a natural boundary between north and south China,it plays an important role in climate change research. Tree-ring have been used as an important archive in paleoclimate research for its attribute as precise dating, advanced resolution and comparability with meteorological data. Abies fargesii in Niubeiliang Natural Reserve is very sensitive to climate change and was used to study the differential characteristics of climate response at different elevations in this study. 122 tree-ring cores were collected at the elevations of 2 400 m, 2 500 m and 2 600 m. According to the method of dendrochronology, all of tree-ring cores were dried, mounted, surfaced and cross-dated. The tree-ring of each core was subsequently measured with a resolution of 0.001 mm by LINTAB, the quality control of cross-dating was carried out by using the COFECHA program, detrending and tree-ring chronologies developing was established by ARSTAN program which enabled the age and size related variations in the tree-ring widths to be removed. Then 2 kinds of chronologies including standard chronology and residual chronology were developed, among which residual chronology was chosen for our study because it contained superior statistical characteristic values. Finally, correlation analysis was carried out and multiple linear regression models was established respectively, in order to contrast characteristic parameters of tree-ring width chronologies for Abies fargesii from different elevations in Qinling Mountains at the upper timberline as well as their response pattern to climate change. The results show, with the increase of elevation, the sensitivity of tree growth to climate factors becomes higher; however, the consistency of the series and the amount of the climate information decreases first and then increases. In general, the arboreal radial growth is more sensitive to temperature than to precipitation, correlation coefficient of tree-ring width indices and temperature increases with the increase of elevation. The sensitive period is from February to August in current year. The chronology of high elevation presents a significant positive correlation with the air temperature of August in current year, while the chronology of middle elevation presents a significant positive correlation with the average precipitation from March to April in current year. Under the influence of the lagging effect of temperature in previous year, the chronology of low elevation presents a significant positive correlation with the average precipitation from January to February in current year. The contribution of each factor to the low, medium and high altitude model was evaluated through regression analysis, and the comprehensive effect of multiple climatic factors on the tree growth was visually reflected. The variation trend of contrast significantly factor reveals that climate change could promote growth season of Abies fargesii in advance, but tree growth dynamic varies at different elevations. The results above show that at the timberline of the study area, Abies fargesii growth at different altitudes may had different response mechanisms to global change.