Latitudinal and elevational gradients both represent thermal gradients. Assessing the consistency of the relationships between phylogenetic structure and climate between latitudinal and elevational gradients can provide insight into the mechanisms driving assembly of species from regional pools into local assemblages. The aim of this study is to compare patterns of phylogenetic structure measures for angiosperm tree species between latitudinal and elevational gradients, using a dataset of angiosperm tree species in 14 092 forest plots in eastern North America. We assessed whether these two gradients produce similar relationships between climate and phylogenetic structure, hypothesizing that they should differ in magnitude but not direction. We used correlation and regression analyses to assess the relation of measures of phylogenetic structure to elevation, latitude and climatic variables, which included minimum temperature, temperature seasonality, annual precipitation and precipitation seasonality. We found that 1) phylogenetic relatedness of angiosperm trees increases with decreasing temperature along both latitudinal and elevational gradients but the relationship between phylogenetic relatedness and temperature is steeper for elevational gradients than for latitudinal gradients; 2) the tip‐weighted metric of phylogenetic relatedness (nearest taxon index) is more strongly correlated with climatic variables than the basal‐weighted metric of phylogenetic relatedness (net relatedness index); 3) winter cold temperature exerts a stronger effect on community assembly of angiosperm trees than does temperature seasonality. These results suggest that winter cold temperature, rather than temperature seasonality, drives phylogenetic structure of plants in local forest communities, and that species distributions along elevational gradients are more in equilibrium with temperature, compared with those along latitudinal gradients.

中文翻译：

---

北美东部沿纬度和海拔梯度的当地森林群落中被子植物树的系统发生结构

纬度和纬度梯度都代表热梯度。评估系统发育结构与纬度和海拔梯度之间的气候之间的关系的一致性，可以深入了解驱动物种从区域库组装到局部集合的机制。这项研究的目的是使用北美东部14 092个森林地块的被子植物树种数据集，比较纬向和海拔梯度之间被子植物树种的系统发育结构模式。我们评估了这两个梯度是否在气候和系统发育结构之间产生了相似的关系，并假设它们在大小上应有所不同，但方向应不同。我们使用相关和回归分析来评估系统发育结构与海拔，纬度和气候变量之间的关系，其中包括最低温度，温度季节，年降水量和降水季节。我们发现：1）被子植物树的系统发生相关性随着温度的降低而沿纬度和海拔梯度增加，但海拔梯度上的系统发生相关性与温度之间的关系比纬度梯度更陡。2）系统发育相关性的尖端加权度量（最近分类群指数）与系统发育相关性的基础加权度量（净相关性指数）之间的相关性更强。3）冬季低温对被子植物群落组装的影响大于温度季节。这些结果表明，冬季寒冷的温度而不是温度的季节性，而是驱动当地森林群落植物的系统发育结构，与沿纬度梯度的物种分布相比，沿海拔梯度的物种分布与温度更加平衡。