Plant distribution and climate data across western North America

Using an extensive network of occurrence records for 293 plant species collected over the past 40 years across a climatically diverse geographic section of western North America, we find that plant species distributions were just as likely to shift upwards (i.e., towards higher elevations) as downward (i.e., towards lower elevations) – despite consistent warming across the study area. Although there was no clear directional response to climate warming across the entire study area, there was significant region-to region- variation in responses (i.e. from as many as 73% to as few as32% of species shifting upward or downward). To understand the factors that might be controlling region-specific distributional shifts, we explored the relationship between the direction of change in distribution limits and the nature of recent climate change. We found that the direction of distribution limit shifts was explained by an interaction between the rate of change in local summer temperatures and seasonal precipitation. Specifically, species shifted upward at their upper elevational limit when snowfall declined at slower rates and minimum temperatures increased. By contrast, species shifted upwards at their lower elevation limit when maximum temperatures increased or both temperature and precipitation decreased. Our results suggest that future species' elevational distribution shifts will be complex, depending on the interaction between seasonal temperature and precipitation change.基于过去40年间在北美西部气候多样的地理区域内收集的293个植物物种的物种出现记录（occurrence records），我们发现，尽管研究区域内持续存在气候变暖现象，但植物物种的分布向上（即向高海拔区域）移动的概率与向下（即向低海拔区域）移动的概率基本相当。尽管整个研究区域内并未呈现出针对气候变暖的明确方向性响应，但不同区域间的响应存在显著差异——物种向上或向下迁移的比例从多达73%到少至32%不等。为探究可能调控区域特异性分布迁移的关键因素，我们分析了分布边界变化方向与近期气候变化特征之间的关联。研究发现，分布边界的迁移方向可通过局地夏季温度变化速率与季节性降水的交互作用予以解释：具体而言，当降雪下降速率放缓且最低气温升高时，物种在其海拔上限处向上迁移；与之相反，当最高气温升高，或温度与降水均下降时，物种在其海拔下限处向上迁移。本研究结果表明，未来物种的海拔分布迁移将更为复杂，其结果取决于季节性温度与降水变化之间的交互作用。