Alpine timberline is very sensitive to zlimatic change,and has become a focus in global change research.In this study,we developed tree-ring chronologies and age structures for timberline forests in the northern Daxing'all Mountains,to examine timberline dynamics in relation to climatic variability.Our results showed that:1)The statistical characters of the chronologies suggested that the sensitivity of tree growth to environmental changes increased with increasing altitude.2)The correlations between tree-ring width and climatic records showed remarkable altitudinal differences.Tree radial growth was mainly limited by previous August precipitation and previous September temperature at high-elevation sites,however,the importance of these climatic factors decreased with decreasing altitude.In contrast,tree growth was mainly limited by current March temperature at low-elevation site.3) The age structures for the timberline forests suggested that fire disturbance,instead of climatic factors,was the major driver for tree recruitment in the study region.The recruitment patterns differed with tree species and elevation,suggesting the differences in regeneration strategy and cold tolerance for different tree species.4)The timberline dynamic in the study region showed clear differences from that of arid regions in several respects,which may be related to differences in climatic conditions,tree species and recruitment drives.%高山林线植被对气候变化十分敏感,已成为全球变化研究的热点.研究了大兴安岭北部大白山高山林线的树木生长和群落更新动态及其与气候变化、火干扰等因素的关系.结果表明,林线树木的生长对气候变化十分敏感,但其敏感性随着海拔的降低而减弱;在高海拔,林线树木的径向生长与上年生长季后期(8月)降水负相关,而与上年初秋(9月)温度正相关,这限制作用随着海拔的降低而逐渐消失;与此相反,低海拔树木生长与当年冬末春初(3月)的温度负相关,但随着海拔上升这种限制作用消失.分析结果还表明,本地区的群落更新主要受火干扰驱动,而与气候变化没有显著关系.不同树种在火灾后更新的时间存在差异,这种差异又因海拔的不同而异,反映出不同树种的更新策略及对环境变化适应能力的差异.大兴安岭北部的高山林线在树木生长对气候变化的敏感性、与气候因子的关系及群落更新动态等方面均与干旱区林线有明显的差异,这些差异与气候条件、树种、更新驱动力等方面的不同有密切的关系.
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