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）、生物相互作用（biotic interactions）与扩散能力（dispersal ability）共同决定物种的空间分布。理论预测，在严酷气候条件下，非生物约束会划定物种分布范围的边界；而在温和气候条件下，分布边界则由生物相互作用决定；扩散能力则会限制物种分布的两端。然而，针对这三类要素如何共同调控环境梯度下物种分布的实证研究仍较为匮乏。
2. 本研究针对瑞士阿尔卑斯山区域瑞士石松（Pinus cembra）在其海拔分布范围内外的更新限制展开分析，同时综合考察上述三类调控要素。我们既调研了松树的自然更新情况，还开展了种子移植实验，以探究非生物因子（夏季与冬季平均气温、土壤湿度）、生物相互作用（林下植被盖度、冠层盖度、种子捕食压力）以及星鸦（Nucifraga caryocatactes）的种子散布行为，分别或共同对松树定植产生的影响。
3. 研究结果显示，生物相互作用与星鸦的种子散布行为，对瑞士石松在海拔分布上限与下限区域的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，在海拔分布上限区域，限制松树更新的核心因素是扩散限制，而非气温与土壤湿度。
4. 综合分析：本研究证实，此前被认为主要受气候调控的物种，其分布上限实则由生物相互作用与扩散能力共同决定。这意味着，植物为响应气候变暖而发生的潜在分布范围迁移，在很大程度上依赖于种子散播与生物相互作用，而非仅由气候因素决定。