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）共同决定了物种的空间分布格局。理论预测，极端气候条件下非生物限制因子将划定物种分布范围的边界，而气候适宜的生境中则由生物相互作用主导分布范围的界定，扩散能力则会限制物种分布范围的两端。然而，针对这三类因子如何共同作用于环境梯度上的物种的实证研究仍较为稀缺。 2. 本研究针对瑞士阿尔卑斯山区的瑞士石松（Pinus cembra），对其在海拔分布范围内外的种群更新限制因素开展联合探究。我们一方面调查了该松树的自然更新情况，另一方面还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（Spotted nutcracker，Nucifraga caryocatactes）的种子沉积行为，在多大程度上影响了瑞士石松的定植过程。 3. 研究结果显示，在瑞士石松海拔分布范围的上下限区域，生物相互作用与星鸦的种子传播行为均对其更新过程存在显著影响，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为扩散限制，而非气温与土壤湿度条件。 4. 综合分析表明，本研究凸显了生物相互作用与扩散能力在划定物种分布上限时的重要性——此前这类分布上限往往被认为主要受气候因子调控。这一发现意味着，植物为响应气候变暖而发生的潜在分布范围迁移，在很大程度上可能依赖于种子传播与生物相互作用，而非仅取决于气候因子。