Compositional shifts of alpine plant communities across the High Andes

Aim: Climate change is transforming mountain summit plant communities worldwide, but we know little about such changes in the High Andes. Understanding large-scale patterns of vegetation changes across the Andes, and the factors driving these changes, is fundamental to predicting the effects of global warming. We assessed trends in vegetation cover, species richness (SR) and community-level thermal niches (CTN) and tested whether they are explained by summits’ climatic conditions and soil temperature trends.

Location: High Andes

Time period: Between 2011/2012 and 2017/2019

Major taxa studied: Vascular plants

Methods: Using permanent vegetation plots placed on 45 mountain summits and soil temperature loggers situated along a ~6,800 km N-S gradient, we measured species and their percentage cover and estimated CTN in two surveys (intervals between 5-8 years). We then estimated the annual rate of changes for the three variables and used generalized linear models to assess their relationship with rates of change in the locally recorded soil temperatures, annual precipitation, and the minimum air temperatures of each summit.

Results: Over time, there was an average loss of vegetation cover (mean = -0.26 %/yr), and a gain in SR across summits (mean = 0.38 species m2/yr), but most summits had significant increases in SR and vegetation cover. Changes in SR were positively related to minimum air temperature and soil temperature rate of change. Most plant communities experienced shifts in their composition by including greater abundances of species with broader thermal niches and higher optima. However, the measured changes in soil temperature did not explain the observed changes in CTN.

Main conclusions: High-Andean vegetation is changing in cover and SR and is shifting towards species with wider thermal niche breadths. The weak relationship with soil temperature trends could have resulted from the short study period that only marginally captures changes in vegetation through time.

Methods
The information reported here comes from two main sources: (1) Data collected on the field during vegetation surveys (between 2011/2012 and 2017/2019) on permanent vegetation plots plus soil temperature collected in dataloggers installed on each research site across the Andes. (2) Species records obtained from GBIF, TROPICOS, La Paz herbarium (LPB) and ULA -Merida herbarium. These records represent species in the permanent plots during the first and second surveys.

研究背景与目标：气候变化正在重塑全球山地山顶植物群落，但目前对高安第斯山脉（High Andes）的此类变化仍知之甚少。明晰安第斯山脉全域植被变化的大尺度格局及其驱动因子，是预测全球变暖影响的核心前提。本研究评估了植被盖度、物种丰富度（species richness, SR）以及群落水平热生态位（community-level thermal niches, CTN）的变化趋势，并检验这些变化是否可由山顶的气候条件与土壤温度变化趋势所解释。

研究区域：高安第斯山脉

研究时段：2011/2012年至2017/2019年

研究类群：维管植物（vascular plants）

研究方法：本研究依托沿南北向约6800公里梯度布设的45个山地山顶永久植被样方与土壤温度记录仪，在两次间隔5至8年的野外调查中，记录了物种组成及其盖度百分比，并估算了群落水平热生态位（CTN）。随后，我们计算了这三个变量的年变化速率，并采用广义线性模型（generalized linear models）分析其与当地记录的土壤温度变化速率、年降水量以及各山顶的最低气温之间的关联。

研究结果：整体而言，所有山顶的植被盖度平均以每年-0.26%的速率下降，而物种丰富度（SR）则以平均每年0.38种·m⁻²的速率上升，但多数山顶的SR与植被盖度均呈现显著提升。物种丰富度的变化与最低气温及土壤温度变化速率呈显著正相关。多数植物群落的组成发生了偏移，优势类群逐渐替换为热生态位宽度更广、最适温度更高的物种。但本研究观测到的土壤温度变化，无法解释群落水平热生态位（CTN）的观测变化。

主要结论：高安第斯山脉的植被在盖度与物种丰富度（SR）上均发生了变化，且群落正向热生态位宽度更广的物种方向演替。土壤温度变化趋势与植被变化之间的关联较弱，这可能源于本研究周期较短，仅能微弱捕捉植被随时间的变化过程。

方法补充说明：本研究的数据主要来源于两个渠道：（1）2011/2012年至2017/2019年期间，通过野外植被调查获取的永久植被样方数据，以及安第斯山脉各研究点安装的温度记录仪采集的土壤温度数据；（2）从全球生物多样性信息设施（Global Biodiversity Information Facility, GBIF）、TROPICOS、拉巴斯标本馆（La Paz Herbarium, LPB）以及ULA-梅里达标本馆获取的物种记录，这些记录对应两次调查中永久样方内的物种信息。