天山中段树木生长对气候垂直梯度的响应*

文章通过天山中段垂直梯度上多个台站的气候资料,系统分析了不同海拔高度气候变化的时空差异性,以此作为与轮宽资料进行相关分析的基础。进一步利用气候条件较为一致的天山中段鹿角湾、乌鲁木齐河源山区和天池等地森林上限附近树木年轮宽度变化资料,结合前人在这一地区森林内部和森林下限所做的研究,探讨了天山中段树木生长对气候垂直梯度的响应。结果表明,天山山区最大降水高度有明显的季节变化,从而导致气候因子对树木生长影响的复杂性。除了海拔最高的采样点天池(TC)外,其他采样点均与上年8~9月降水总量正相关,与上年7~8月平均温度负相关,与当年4~5月降水总量正相关。而在海拔最高、高山林线附近的采样点与当年2月均温显著正相关,与当年5月气温显著负相关。可以认为,在研究区树木生长主要受到上年7~8月由高温引起的干旱和当年4~5月由降水不足导致的干旱的影响。在接近气候林线处,低温的限制作用才表现出来。

RESPONSES OF TREE GROWTH TO VERTICAL CLIMATE GRADIENT IN THE MIDDLE SECTION OF THE TIANSHAN MOUNTAINS

The climate in the arid zone in Northwest China has been reported to change from warm-dry to warm-humid during the last half century. Therefore, to investigate the factors affecting tree growth is not only significant in explaining the response of vegetation to climatic changes, but also helpful in the estimation of future climatic changes and vegetation responses. Climate and vegetation both have obvious vertical gradient in the arid region in Northwest China. Dendroecological studies across a vertical gradient will be beneficial to a trustable prediction of climatic changes in the future both temporally and spatially.Tree ring cores of Tianshan spruce (Picea schrenkiana) were sampled from four sites close to the upper distribution belt of forest by thes. Material of other two sites in the interior and at the lower limit of the forest belt were obtained from previous studies. All sites are located on the northern slope of the middle section of the Tianshan Mountains. Spatial and temporal variations of temperature and precipitation along an elevational gradient were comprehensively discussed in this study based on nine vertically distributed meteorological stations. As all the stations were located on the northern slope of the Tianshan Mountains, it is suggested that elevation is the preliminary determinant of temperature and precipitation across meteorological stations as well as sample sites. We use the interpolated climatic data from nine stations to correlate with tree ring width indices. Our study results show that: (1) The elevation with maximum precipitation changes seasonally, making the determinant of tree growth in the study area changes across elevation. The months during which tree growth are sensitive to climatic factors are different due to this seasonal patterns of elevation with maximum precipitation; (2) Except the uppermost site, the others are correlated positively with precipitation during August-September of the preceding year, negatively with mean temperature during July-August of the preceding year, and positively with precipitation during April-May of the current year; (3) At the uppermost site which is close to the alpine timberline, the residual chronology is significantly positively correlated with mean temperature in February and negatively with temperature in May of the current year.It is implied that tree growth in the study area is mainly controlled by drought caused by high temperature during July-August of the preceding year as well as by the lack of water during April-May of the current year. Only close to the climatic timberline the limitation of low temperature on tree growth is significant and the limitation of precipitation is not important. So we can infer the response change of tree ring width as the evidence of confirming climate timberline.