贡嘎山树线上方杜鹃灌木径向生长对气候变化的响应特征

Response of Radical Growth of Rhododendron faberi subsp.Prattii to Climate Change above Treeline in the Gongga Mountain,China

气候变暖深刻影响着高山树线上方的灌木生长,然而目前其对气候变化的响应特征仍不清楚。本文以贡嘎山树线上方的大叶金顶杜鹃(Rhododendron faberi subsp.Prattii)为研究对象,分别采用负指数函数法(CD)、断面积增量(BAI)以及区域曲线标准法(RCS)去除生长趋势,建立标准化年表,分析大叶金顶杜鹃生长特征,并用相关分析、偏相关分析和滑动相关分析来探讨大叶金顶杜鹃径向生长与气候因子的关系。结果如下:(1)Mann-Kendall趋势检验结果表明1980—2018年断面积增量BAI增加趋势最为显著;(2)相关分析结果表明BAI与前一年7月最高温度、前一年9月平均温度、当年7月和9月最高温度以及平均温度呈现显著正相关关系,与前一年以及当年6月、7月、9月相对湿度呈现显著负相关关系;在季节尺度上,BAI与前一年7—11月平均温度、当年7—9月平均温度和当年4—9月最高温度呈现显著正相关,与前一年7—9月以及当年2—9月平均相对湿度显著负相关;(3)响应函数和偏相关分析分析结果表明当年7月最高温度是影响杜鹃灌木径向生长的关键生态因子;(4)滑动相关分析揭示了在全球变暖背景下,分布在贡嘎山树线上方的大叶金顶杜鹃的径向生长将会增加。本研究结果有助于更加全面地理解与预测气候变化对树线上方灌木生长的影响。

Global warming have a significant effect on shrub growth above treelines,whereas its response to climate change still remains unclear.In order to determine shrub radial growth trends and explore its responses to climate,standard dendrochronological procedures were performed using tree-ring materials of Rhododendron faberi subsp.Prattii(RF)collected above alpine treelines in Gongga Mountain.Three detrending strategies,including conservative detrending(CD),regional curve standardization(RCS)and basal area index(BAI)were used to remove age-related growth trends and construct standardized RF ring-width chronologies.Pearson correlation coefficients,partial and moving correlation analyses were conducted to research the connection of the RF radial growth and climate variabilities.We conclude that:(1)The area of radial growth enhancement was most significant for BAI chronology as suggested by Mann-Kendall trend test.(2)Pearson correlation analysis suggested that the radial growth of RF was significantly and positively correlated with July maximum temperature and mean September temperature of the previous year,both mean and maximum temperature in July and September of the current year.The radical growth of RF was significantly and negatively associated with relative humidity in June,July,and September of both the previous and current year.The radial growth of RF was also negatively correlated with the relative humidity of June,July and September in both the previous and current year.Climatic response at seasonal scale was explored,which suggested that BAI chronology was significantly and positively associated with July-November mean temperature of the previous year,July-September mean temperature and April-September maximum temperature of the current year.(3)The response function and partial correlations suggested that the July maximum temperature of the current year was the key factor dominating the RF radial growth in Gongga Mountain.(4)The moving correlation analysis implied the RF above treeline in Gongga Mountain increased with climate warming.This study could contribute to understand and predict the climatic response of shrub growth above treelines.