Recent climate warming forces contrasting growth responses of white spruce at treeline in Alaska through temperature thresholds
Recent climate warming forces contrasting growth responses of white spruce at treeline in Alaska through temperature thresholds
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DOI：
10.1111/j.1365-2486.2004.00826.x
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发表时间：
2004-10
影响因子：
11.6
通讯作者：
M. Wilmking;G. Juday;V. Barber;Harold S. J. Zald
中科院分区：
文献类型：
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作者：
M. Wilmking;G. Juday;V. Barber;Harold S. J. Zald
人们普遍认为北部和高纬度高山林线受到可用温暖的限制。大多数关于林线树木生长与气候相互作用的研究以及利用树木年代学进行气候重建的研究都报告了林线树木对温暖温度的积极生长反应。然而，树线树木对气候的总体反应在很大程度上仍未得到检验。我们在布鲁克斯山脉和阿拉斯加山脉的 13 个林线地点系统地采样了 1558 棵白云杉。我们对林线气候变暖的积极和消极生长反应的研究结果挑战了人们普遍认为北极林线树木随着气候变暖而生长得更好的假设。 7 月的平均气温较高，导致阿拉斯加林线地区 40% 的白云杉生长减少，而温暖的泉水则促进了另外 36% 的树木生长，其中 24% 的树木与气候没有显着相关性。尽管这些相反的生长反应存在于所有采样地点，但它们的相对比例在不同地点之间有所不同，并且生长反应和地点内的景观位置之间没有总体明确的关系。在我们的样本中，生长的增加和减少出现在特定温度指数值（温度阈值）之上，这种情况在 20 世纪末期更为频繁地发生。与之前的发现相反，温度解释了 1950 年后径向生长的更多变化。如果不考虑这些相反的响应和温度阈值，基于年轮宽度的气候重建将错误校准过去的气候，生物地球化学和动态植被模型将高估未来变暖情景下的碳吸收和林线推进。
Northern and high‐latitude alpine treelines are generally thought to be limited by available warmth. Most studies of tree‐growth–climate interaction at treeline as well as climate reconstructions using dendrochronology report positive growth response of treeline trees to warmer temperatures. However, population‐wide responses of treeline trees to climate remain largely unexamined. We systematically sampled 1558 white spruce at 13 treeline sites in the Brooks Range and Alaska Range. Our findings of both positive and negative growth responses to climate warming at treeline challenge the widespread assumption that arctic treeline trees grow better with warming climate. High mean temperatures in July decreased the growth of 40% of white spruce at treeline areas in Alaska, whereas warm springs enhance growth of additional 36% of trees and 24% show no significant correlation with climate. Even though these opposing growth responses are present in all sampled sites, their relative proportion varies between sites and there is no overall clear relationship between growth response and landscape position within a site. Growth increases and decreases appear in our sample above specific temperature index values (temperature thresholds), which occurred more frequently in the late 20th century. Contrary to previous findings, temperature explained more variability in radial growth after 1950. Without accounting for these opposite responses and temperature thresholds, climate reconstructions based on ring width will miscalibrate past climate, and biogeochemical and dynamic vegetation models will overestimate carbon uptake and treeline advance under future warming scenarios.