天山山区不同海拔高度雪岭云杉径向生长对气候变化的响应

Climate change alters the radial growth of Picea schrenkiana along an elevational gradient in the Tianshan Mountains

关键词:  天山山脉  雪岭云杉  树木年轮  海拔梯度  气候响应

Key words:  Tianshan Mountains  Picea schrenkiana  tree ring  altitude gradient  climate response

摘要:

研究气候变暖条件下不同海拔高度树木径向生长与气候因子的响应差异，对正确认识森林动态变化及分布格局具有重要意义。基于树轮宽度资料，使用主成分分析、相关性分析等方法，探讨1962—2005年天山不同海拔高度雪岭云杉（Picea schrenkiana）径向生长和气候要素的响应关系及响应稳定性。结果表明：（1）天山山区雪岭云杉径向生长变化与海拔高度有直接联系，且海拔2.4 km以上树木径向生长量呈增加趋势，海拔2.4 km以下的样点树木径向生长增量逐渐减小。（2）在海拔2.6 km左右，雪岭云杉的径向生长与上年生长季初期气温呈显著正相关；而在海拔2.4 km以下区域，树轮宽度年表与上年生长季气温呈负相关关系。其中，海拔2.1 km及以下样点的树木径向生长同时受上年生长季气温和降水的共同影响，这一现象在海拔1.7 km以下区域表现得尤为显著。（3）海拔2.6 km左右雪岭云杉径向生长与上年夏季气温的正响应增强。随着气候暖湿化，海拔越低的区域，干旱胁迫作用越明显，且这种关系在海拔1.7 km以下的区域表现更加稳定。

Abstract:

Background, aim, and scope Variation in altitude has a major effect on tree growth, and the structure of forest ecosystems might be affected by climate warming. There is thus a need to determine the effects of altitudinal variation in climatic factors on tree radial growth under climate warming to shed light on future changes in forest growth dynamics and distribution patterns. Here, we analyzed the relationship between the tree-ring width of Picea schrenkiana and various climatic factors along an elevational gradient in the Tianshan Mountains using a large dendrochronological dataset. Materials and methods We used principal component analysis and correlation analysis to clarify the relationships between the radial growth of P. schrenkiana and climatic factors along an elevational gradient in the Tianshan Mountains from 1962 to 2005. Results (1) A direct relationship between the radial growth of P. schrenkiana in the Tianshan Mountains and altitude was observed. Increases in the radial growth of trees at four sampling points above 2.4 km were observed, and the radial growth of trees was reduced below 2.4 km. (2) The radial growth of P. schrenkiana at approximately 2.6 km was positively correlated with the temperature of the previous growing season (May—June of the previous year). At sampling points below 2.4 km, the tree-ring width chronology was negatively correlated with the temperature of the previous growing season. The radial growth of trees below 2.1 km was mainly affected by the joint effect of temperature and precipitation in the growing season of the previous year. This effect was particularly pronounced in areas below 1.7 km. (3) Moving correlation analysis revealed that the strength of the positive relationship between the radial growth of P. schrenkiana and the temperature of the previous summer was enhanced at an altitude of approximately 2.6 km. The positive relationship between the radial growth of P. schrenkiana and precipitation weakened at approximately 2.4 km, as the climate became warmer and wetter over the study period. Below 2.1 km, the negative relationship between the tree-ring width chronology and temperature weakened, and the positive relationship with precipitation was enhanced in some periods. This response relationship was more stable in areas below 1.7 kilometers Discussion The growth and distribution of P. schrenkiana were directly affected by altitude. The temperature of the previous growing season affected the growth of P. schrenkiana in the current year. In high-altitude areas, increases in temperature during the growing season promoted the radial growth of P. schrenkiana. Below 2.4 km, the radial growth of P. schrenkiana was limited by drought stress. Increases in temperature and humidity will enhance the photosynthesis of P. schrenkiana at high altitudes. However, the increase in summer precipitation in low-altitude areas does not offset the increase in evaporation caused by rising temperatures, indicating that the magnitude of the negative effect of increased drought stress on P. schrenkiana was greater than the magnitude of the positive effect of increased precipitation. Conclusions Increases in the radial growth of P. schrenkiana in the area above 2.4 km were particularly pronounced over the study period. In the Tianshan Mountains, the radial growth of P. schrenkiana was primarily affected by climatic factors of the previous growing season. Increases in temperature during the previous growing season promoted the radial growth of P. schrenkiana in areas above 2.4 km and inhibited radial growth in areas below 2.1 km. Recommendations and perspectives Continued warming might lead to shifts in the altitudinal distribution of P. schrenkiana in the Tianshan region. Overall, our findings have implications for dendrochronological reconstructions of the historical climate in the study area and forest ecological protection in the Tianshan region.