Lange Jelena, Buras Allan, Cruz-García Roberto, Gurskaya Marina, Jalkanen Risto, Kukarskih Vladimir, Seo Jeong-Wook, Wilmking Martin
Institute of Botany and Landscape Ecology, University of Greifswald, Greifswald, Germany.
Forest Ecology and Forest Management, Wageningen University and Research, Wageningen, Netherlands.
Front Plant Sci. 2018 Nov 8;9:1597. doi: 10.3389/fpls.2018.01597. eCollection 2018.
Tree growth at northern boreal treelines is generally limited by summer temperature, hence tree rings serve as natural archives of past climatic conditions. However, there is increasing evidence that a changing summer climate as well as certain micro-site conditions can lead to a weakening or loss of the summer temperature signal in trees growing in treeline environments. This phenomenon poses a challenge to all applications relying on stable temperature-growth relationships such as temperature reconstructions and dynamic vegetation models. We tested the effect of differing ecological and climatological conditions on the summer temperature signal of Scots pine at its northern distribution limits by analyzing twelve sites distributed along a 2200 km gradient from Finland to Western Siberia (Russia). Two frequently used proxies in dendroclimatology, ring width and maximum latewood density, were correlated with summer temperature for the period 1901-2013 separately for (i) dry vs. wet micro-sites and (ii) years with dry/warm vs. wet/cold climate regimes prevailing during the growing season. Differing climate regimes significantly affected the temperature signal of Scots pine at about half of our sites: While correlations were stronger in wet/cold than in dry/warm years at most sites located in Russia, differing climate regimes had only little effect at Finnish sites. Both tree-ring proxies were affected in a similar way. Interestingly, micro-site differences significantly affected absolute tree growth, but had only minor effects on the climatic signal at our sites. We conclude that, despite the treeline-proximal location, growth-limiting conditions seem to be exceeded in dry/warm years at most Russian sites, leading to a weakening or loss of the summer temperature signal in Scots pine here. With projected temperature increase, unstable summer temperature signals in Scots pine tree rings might become more frequent, possibly affecting dendroclimatological applications and related fields.
北方寒温带树线地区的树木生长通常受夏季温度限制，因此树木年轮成为过去气候条件的天然记录档案。然而，越来越多的证据表明，夏季气候的变化以及某些微生境条件会导致树线环境中树木的夏季温度信号减弱或消失。这种现象给所有依赖稳定温度-生长关系的应用带来了挑战，比如温度重建和动态植被模型。我们通过分析沿着从芬兰到西西伯利亚（俄罗斯）2200公里梯度分布的12个地点，测试了不同生态和气候条件对苏格兰松在其北半分布界限处夏季温度信号的影响。在树木年代学中两个常用的指标，年轮宽度和最大晚材密度，分别针对（i）干燥与湿润微生境以及（ii）生长季节盛行干燥/温暖与湿润/寒冷气候状况的年份，与1901 - 2013年期间的夏季温度进行了相关性分析。不同的气候状况在大约一半的研究地点显著影响了苏格兰松的温度信号：在俄罗斯的大多数地点，湿润/寒冷年份的相关性比干燥/温暖年份更强，而不同的气候状况对芬兰的地点影响很小。两个树木年轮指标受到的影响方式相似。有趣的是，微生境差异显著影响了树木绝对生长，但对我们研究地点的气候信号影响较小。我们得出结论，尽管处于树线附近位置，但在大多数俄罗斯地点，干燥/温暖年份似乎超出了生长限制条件，导致这里苏格兰松的夏季温度信号减弱或消失。随着预计的气温升高，苏格兰松树轮中不稳定的夏季温度信号可能会更频繁出现，这可能会影响树木年代学应用及相关领域。
