摘要:高山林线的形成机理一直是高山生态学讨论的一个焦点问题，其中林线树木生长的阈值温度一直是研究热点。利用川西高原九寨沟弓杠岭林线岷江冷杉（Abies faxoniana）树木径向生长数据，通过树轮宽度-气候因子关系分析，探讨阈值温度和积温对林线岷江冷杉径向生长的影响。结果表明：林线岷江冷杉径向生长主要受到温度限制，其中林线岷江冷杉径向生长与当年生长季（7、8和9月）、冬季（12、1和2）及上一年9、10月温度显著正相关（P < 0.05），但与降水的相关性较弱。林线岷江冷杉径向生长与不同起始温度的初日负相关，与不同起始温度的终日正相关，且与9.5℃阈值温度的初日负相关最强（P < 0.05），与6.5℃阈值温度的终日正相关最强（P < 0.05）。林线岷江冷杉径向生长还与7-9.5℃的积温及9.5℃持续天数显著正相关（P < 0.05），说明7-9.5℃可能是形成层活动的阈值温度，尤其7℃可能是林线岷江冷杉生长的起始温度。林线岷江冷杉生长期从4月中旬开始到10月初结束，随着1980年后温度的显著升高，生长期活动积温开始增加，生长期初日提前（4.6d/10a，r²=0.19，P=0.01），生长期终日延后（1.8 d/10a），使得生长期延长（6.4 d/10a），进而对林线岷江冷杉径向生长有显著的促进作用。未来气候变暖可能会使川西林线树木生长增加，林线可能会上移。



Abstract:The formation of alpine timberline has always been in focus in alpine mountain forest ecology, and the threshold temperature of tree growth at timberline has always been a hot spot of research. We used the radial growth data of Minjiang fir (Abies faxoniana) at the timberline of Gonggang Mountain, Jiuzhaigou, Western Sichuan Plateau to test the effects of threshold and accumulated temperatures on Minjiang fir growth through the response function analysis. The results showed that the radial growth of Minjiang fir is mainly limited by temperature. Furthermore, the radial growth positively correlated with temperatures during the growing season (July-September), during winter (previous December-February), and in September and October of the previous year (P < 0.05). However, the effect of precipitation on Minjiang fir growth was weak. The fir radial growth negatively and positively correlated with the first and last days of growth at different threshold temperatures, respectively. The strongest correlations between fir growth and the first and last days of growth at different threshold temperatures occurred at 9.5 and 6.5℃, respectively. The fir radial growth at timberline also positively correlated with the accumulated temperatures (starting at 7, 7.5, 8, 8.5, 9, and 9.5℃) and the duration at 9.5℃ (P < 0.05), which indicates that 7-9.5℃ might be the threshold temperature of cambium activity, especially the temperature of 7℃ might be the initial temperature of photosynthesis and growth of Minjiang fir at the timberline. The growth period of Minjiang fir at timberline is from the mid-April to the beginning of October. With a significant increase in temperature after 1980, the accumulated temperature during the growing season began to increase, the first day of growth has shifted to an earlier date (4.6 d/10a, r²=0.19, P=0.01), the last day of growth has been postponed (1.8 d/10 a, r²=0.04, P=0.25), the growing season has become longer (6.4 d/10 a, r²=0.19, P=0.01), thus, significantly promoting the radial growth of Minjiang fir at the timberline. The results suggest that future climate warming might increase tree growth at the timberline in the West Sichuan Plateau, and the timberline might move upward.





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