G-TREE: Global Treeline Range Expansion Experiment Davos, Switzerland

Background information Climate change-induced range expansion of treeline populations depends on their successful recruitment, which requires dispersal of viable seeds followed by successful establishment of individual propagules. The Global Treeline Range Expansion Experiment (G-TREE) is a global initiative involving researchers from Europe, North America, Australia and New Zealand (Brown et al., 2013). At 15 alpine and Arctic treeline sites worldwide the mechanisms determining the elevational and latitudinal distribution of tree populations are studied using a standardized experimental approach. In summer 2013, a multifactorial seedling recruitment experiment has been established at the Stillberg ecological treeline research site. The aim of this experiment, is to quantify the effect of multiple abiotic and biotic drivers on emergence, survival, and growth of *Larix decidua* and *Picea abies* seedlings in replicated plots along an elevation gradient with three sites below (1930 m a.s.l.), at (2090 m a.s.l.), and above treeline (2410 m a.s.l.; Frei et al., 2018). All plots have been surveyed annually to count seedlings and to measure their total height. Additional environmental factors, such as soil temperature, have been recorded. Experimental design The Stillberg research area is located in the Eastern Swiss Alps near Davos, Switzerland. The site has been used for several long-term monitoring as well as experimental studies for the last four decades. Our G-TREE experiment consists of a lowest site located in a subalpine Larch-Spruce forest (*Larici-Picetum*) dominated by *Larix decidua* and *Picea abies* (1930 m a.s.l.), a transition zone site dominated by alpine shrubs (2100 m a.s.l.), and an uppermost site in an alpine meadow with some dwarf shrubs (2390 m a.s.l.). The three experimental sites were set up following the standard protocol of the global G-TREE initiative (Brown et al., 2013). In a split-plot design, 20 plots (224 cm × 45 cm) were established at each site, which were randomly assigned to the 2 × 2 treatment combinations of the main factors seeding and scarification (i.e. seeding and scarification, seeding only, scarification only, and full control), resulting in five replications per main treatment combination. Each plot was divided into 16 split-plots (22.5 cm × 28 cm), to which treatment combinations of four additional two-level factors species (larch and spruce), provenance (low- and high-elevation), herbivore exclosure (with and without exclosure), and seeding year (2013, 2014) were randomly assigned, which resulted in a total of 960 split-plots (Details see Frei et al. 2018). Data description All plots have been surveyed annually to count seedlings and to measure their total height. Seedling height was assessed with a hand ruler as the total length from the original emerging point to the apical meristem (Details see Frei et al. 2018). Additionally, soil temperature at each site, has been continuously recorded since 2013. Here, we present data from eight years (2013–2021).背景信息 气候变化驱动的林线种群范围扩张，取决于其成功的自然更新，这需要有活力的种子完成扩散，并实现单个繁殖体的成功定植。全球林线范围扩张实验（Global Treeline Range Expansion Experiment, G-TREE）是一项由欧洲、北美、澳大利亚及新西兰研究人员参与的全球性研究计划（Brown等，2013）。该项目在全球15个高山与北极林线样地中，采用标准化实验方法，探究决定树木种群海拔与纬度分布的机制。2013年夏季，研究团队在Stillberg生态林线研究样地建立了多因素幼苗更新实验。本实验旨在量化多种非生物与生物驱动因子对欧洲落叶松（*Larix decidua*）和挪威云杉（*Picea abies*）幼苗的出苗、存活与生长的影响，实验设置了沿海拔梯度分布的重复样地，包含3个海拔位点：林线以下（1930 m a.s.l.）、林线处（2090 m a.s.l.）以及林线以上（2410 m a.s.l.；Frei等，2018）。所有样地每年均开展调查，统计幼苗数量并测量其总高度，同时记录土壤温度等额外环境因子。 实验设计 Stillberg研究区域位于瑞士达沃斯附近的瑞士东部阿尔卑斯山区，近四十年来已被多次用于长期监测与实验研究。本G-TREE实验包含3个样地：最低位点为以欧洲落叶松和挪威云杉为优势种的亚高山落叶松-云杉林（*Larici-Picetum*，1930 m a.s.l.），过渡带样地以高山灌丛为优势种（2100 m a.s.l.），最高位点为带有少量矮灌的高山草甸（2390 m a.s.l.）。三个实验样地均遵循全球G-TREE倡议的标准规程设置（Brown等，2013）。 采用裂区设计，每个样地设置20个样方（224 cm × 45 cm），并将其随机分配至播种与土壤划痕（即播种+土壤划痕、仅播种、仅土壤划痕以及完全对照组）这2×2主因子处理组合，每个主处理组合设置5次重复。每个样方被划分为16个副样区（22.5 cm × 28 cm），并随机分配4个附加两水平因子的处理组合：物种（落叶松与云杉）、种源（低海拔与高海拔）、草食动物排除（有排除与无排除）以及播种年份（2013、2014），最终共计960个副样区（详细信息参见Frei等，2018）。 数据描述 所有样地每年均开展调查，统计幼苗数量并测量其总高度。幼苗高度采用手持钢尺测量，即从幼苗初始出苗点到顶端分生组织的总长度（详细信息参见Frei等，2018）。此外，各点位的土壤温度自2013年起持续记录。本数据集涵盖2013—2021年共8年的观测数据。