Université Clermont Auvergne, CNRS, GEOLAB, F-63000, Clermont-Ferrand, France.
Centre de Recherches sur les Ecosystèmes d'Altitude (CREA), Observatoire du Mont-Blanc, 74400, Chamonix, France.
Am J Bot. 2020 Apr;107(4):607-617. doi: 10.1002/ajb2.1459. Epub 2020 Apr 1.
Mountain ecosystems are particularly sensitive to climate change. However, only a very small number of studies exist so far using annually resolved records of alpine plant growth spanning the past century. Here we aimed to identify the effects of heat waves and drought, driven by global warming, on annual radial growth of Rhododendron ferrugineum.
We constructed two century-long shrub ring-width chronologies from R. ferrugineum individuals on two adjacent, north- and west-facing slopes in the southern French Alps. We analyzed available meteorological data (temperature, precipitation and drought) over the period 1960-2016. Climate-growth relationships were evaluated using bootstrapped correlation functions and structural equation models to identify the effects of rising temperature on shrub growth.
Analysis of meteorological variables during 1960-2016 revealed a shift in the late 1980s when heat waves and drought increased in intensity and frequency. In response to these extreme climate events, shrubs have experienced significant changes in their main limiting factors. Between 1960 and 1988, radial growth on both slopes was strongly controlled by the sum of growing degree days during the snow free period. Between 1989 and 2016, August temperature and drought have emerged as the most important.
Increasing air temperatures have caused a shift in the growth response of shrubs to climate. The recently observed negative effect of high summer temperature and drought on shrub growth can, however, be buffered by topographic variability, supporting the macro- and microrefugia hypotheses.
山地生态系统对气候变化特别敏感。然而，迄今为止，使用跨越过去一个世纪的高山植物生长的年度分辨率记录的研究非常少。在这里，我们旨在确定由全球变暖驱动的热浪和干旱对高山报春 Rhododendron ferrugineum 的年径向生长的影响。
我们从法国南部阿尔卑斯山两个相邻的北坡和西坡的高山报春个体中构建了两个长达一个世纪的灌木年轮宽度年表。我们分析了 1960-2016 年期间可用的气象数据（温度、降水和干旱）。使用自举相关函数和结构方程模型分析气候-生长关系，以确定温度升高对灌木生长的影响。
对 1960-2016 年气象变量的分析表明，在 20 世纪 80 年代末发生了转变，当时热浪和干旱的强度和频率增加。为了应对这些极端气候事件，灌木的主要限制因素发生了重大变化。在 1960 年至 1988 年期间，两个山坡上的径向生长都强烈受到无雪期生长度日总和的控制。在 1989 年至 2016 年期间，8 月的温度和干旱成为最重要的因素。
空气温度的升高导致了灌木对气候的生长反应发生了转变。然而，最近观察到的夏季高温和干旱对灌木生长的负面影响可以通过地形变异性来缓冲，这支持了宏观和微观避难所假说。
