Data from: Biotic interactions and seed deposition rather than abiotic factors determine recruitment at elevational range limits of an alpine tree

1. Abiotic factors, biotic interactions and dispersal ability determine the spatial distribution of species. Theory predicts that abiotic constraints set range limits under harsh climatic conditions and biotic interactions set range limits under benign climatic conditions, whereas dispersal ability should limit both ends of the distribution. However, empirical studies exploring how these three components jointly affect species across environmental gradients are scarce. 2. Here we present a study that jointly examines these factors to investigate the constraints of the recruitment of Swiss stone pine (Pinus cembra) across and beyond its elevational range in the Swiss Alps. We investigated the natural recruitment of pines and additionally conducted seed transplant experiments to test how much abiotic factors (mean summer and winter temperatures, soil moisture), biotic interactions (understorey vegetation cover, canopy cover, seed predation) and / or seed deposition by the Spotted nutcracker (Nucifraga caryocatactes) affect pine establishment. 3. We found significant effects of biotic interactions and seed deposition by Spotted nutcrackers on the recruitment of Swiss stone pine at both the upper and lower elevational range, but could not detect significant effects of abiotic factors. Importantly, dispersal limitation rather than temperature and soil moisture restricted the recruitment of pines at the upper elevational range. 4. Synthesis. Our study highlights the importance of biotic interactions and dispersal ability in setting the upper range limits of species that have been regarded as mainly controlled by climate. This suggests that potential range shifts of plants in response to climate warming may strongly depend on seed dispersal and biotic interactions and not only on climatic factors.

1. 非生物因子（Abiotic factors）、生物交互（Biotic interactions）与扩散能力（Dispersal ability）共同决定物种的空间分布。理论预测，非生物约束会在严酷气候条件下划定物种分布范围的边界，生物交互则在温和气候条件下划定分布边界，而扩散能力会限制物种分布的两端。然而，探究这三个组分如何共同影响环境梯度下物种分布的实证研究仍较为稀缺。
2. 本研究针对上述研究缺口，联合考察这三类因子，以探究瑞士阿尔卑斯山内及超出其海拔分布范围的瑞士石松（Pinus cembra）的更新限制机制。我们调查了松树的自然更新情况，并额外开展了种子移植实验，以检验非生物因子（夏季与冬季平均气温、土壤含水量）、生物交互（林下植被盖度、林冠盖度、种子捕食）以及/或星鸦（Nucifraga caryocatactes）的种子传播在多大程度上影响松树定植。
3. 研究结果显示，生物交互与星鸦的种子传播对海拔分布上下限处的瑞士石松更新均存在显著影响，但未检测到非生物因子的显著作用。尤为关键的是，在海拔分布上限处，限制松树更新的因素为扩散限制，而非气温与土壤含水量。
4. 研究总结。本研究凸显了生物交互与扩散能力在划定此前被认为主要受气候调控的物种分布上限中的重要性。这表明，植物响应气候变暖的潜在分布区转移，可能在很大程度上依赖于种子传播与生物交互，而非仅取决于气候因子。