祁连山中段青海云杉高山林线交错区树轮宽度与气候变化的关系

通过对祁连山中段青海云杉高山林线交错区进行取样，研究了交错区内4个不同海拔树木生长与气候变化的关系。结果表明:在林线交错区内，树木生长对气候变化的敏感性不高，年表统计特征沿海拔并没有一致的变化趋势。气候对树木生长的影响表现出非常明显的“生长滞后效应”，所有样地的轮宽指数与上一年10月的降水显著正相关，多数样地的轮宽指数与上一年7、8月的温度显著负相关，后者体现了有效水分供应的限制作用。同时，多数样地的轮宽指数与当年2月降水显著负相关。整个林线交错区的树轮生长主要受生长季之前(上一生长季和秋冬季)的气候指标的影响，而与当年生长季气候没有明显的联系。本文和相关研究发现的林线树木生长对气候变化并不敏感的现象，与高山林线主要受生长季温度限制的传统认识明显不同。 

Alpine timberline ecotone tree growth in relation to climatic variability for Picea crassifolia forests in the middle Qilian Mountains, northwestern China.

The Picea crassifolia forests at the alpine timberline ecotone in the middle Qilain Mountains of northwestern China were examined in this study. Tree-ring cores were sampled at four different altitudes to examine the relationship between tree growth and climatic variability. The statistical characters of the chronologies suggested that the sensitivity of tree growth to climatic variability was generally low across the alpine timberline ecotone,and did not show clear trend along the altitudinal gradient,probably due to the short vertical gradient. Tree radial growth in the timberline ecotone was strongly associated with climatic indices before growing season. Tree-ring width was positively related to precipitation in the previous October,while negatively correlated with temperature in the previous July and August for most plots,with the later actually reflecting the effect of water availability in limiting tree growth in this semi-arid region.Meanwhile,tree growth was also negatively related to the current February temperature. Our results did not show clear relationship between tree-ring width and climatic condition in the current year growing season,suggesting that tree growth in timberline ecotone was not limited by growing season temperature in our study site. We reviewed existing evidence which showed that timberline tree growth was sometimes not sensitive to temperature changes in growing season.