西藏八宿川西云杉树线过渡区树木生长与气候关系的一致性

Relationship of tree growth and climatic factors at treeline of Picea likiangensis var. balfouriana forest in Basu County, Xizang

与传统方法相比,利用树木年轮学方法研究树线过渡区树木生长温度敏感性高低的问题更注重比较树木个体间的生长情况,从各个树轮序列间的生长一致性程度和树轮序列对气候因素(气温、降水)的响应一致性程度可探讨树线过渡区树木生长的温度敏感性。为了认识高山树线过渡区内树木生长的温度敏感性问题,选择西藏昌都地区八宿县的一条川西云杉树线过渡区为研究对象,比较了过渡区内树木个体间的生长一致性,分析了树木生长与气候因素的相关性及其在个体间的异同。结果显示:树线过渡区内树轮生长在个体间的一致性较低,树轮生长与气温的关系在树木个体间的一致性也较低,而树轮生长与当年4–9月降水的关系相对较强。西藏八宿树线过渡区属于干旱区,相对于气温而言,降水对树木生长的影响更大。此外,小生境的异质性及干扰事件的发生也有可能降低树木对温度的敏感性。在全球变暖及极端气候事件增加的背景下,树木生长的温度敏感性被高估可能会导致对树线过渡区位置及树线过渡区内群落生产力等的预测产生偏差,这一问题应该在区域生态模拟研究和相关林业经营与管理上得到重视。

Aims Temperature is usually hypothesized to be the primary climate factor limiting tree growth at high eleva-tion. We test this hypothesis by investigating the tree growth and climate factors at treeline ecotone on the south-eastern Xizang Plateau. Methods Tree-ring samples of Picea likiangensis var. balfouriana were collected at treeline ecotone in Kese Village, Bangda Town, Basu County, Xizang. These samples were polished, measured, crossdated, and detrended to produce sequences of tree-ring width indices for each individual sample. Pearson correlation coefficients were calculated among each pair of the individual samples. Correlation between tree-ring sequences and climatic factors （air temperature and precipitation） were also calculated to examine treering responses to air temperature, precipitation. Important findings At the treeline ecotone of P. likiangensis var. balfouriana, air temperature had little effect on tree-ring growth. Precipitation in growing season had a strong effect on tree growth with large variation among individual trees. Our results suggest that temperature sensitivity of tree growth might be over-estimated at treeline ecotone on the southeastern Xizang Plateau.