Data from: "Declines in low-elevation subalpine tree populations outpace growth in high-elevation populations with warming"

This data package contains model data that were used to support conclusions drawn in “Declines in low-elevation subalpine populations outpace growth in high-elevation populations with warming”, by Conlisk et al. 2017. Experimental data collected at field sites within the Alpine Treeline Warming Experiment (ATWE), and data from long-term observational plots were collected on Niwot Ridge, Colorado, USA and used to formulate models contained within the folder “Model_archive” in the zipped folder “Conlisk_etal_JEcol2017_model_archive12022020.zip”. The contents of this compressed folder are described in the data user's guide attached to this archive. There are two folders within the zipped folder - “EngelmannSpruce” and “LimberPine” - for each of the two species in the paper. Models are stored as text files and .sch files can also be opened as text files. However, please note that all these files are specific to the RAMAS Metapop population modeling software, and you will need the program in order to be able to run these models. There are two separate documents, both named “Conlisk_JofEcology_SI_01262017” within “Model_archive”. One is a Microsoft Word file, and the other is a PDF. The former can be opened with Microsoft Word, and the latter can be opened by Adobe Acrobat Reader, or any software compatible with a PDF. ------------------ 1. Species distribution shifts in response to climate change require that recruitment increase beyond current range boundaries. For trees with long lifespans, the importance of climate-sensitive seedling establishment to the pace of range shifts has not been demonstrated quantitatively. 2. Using spatially explicit, stochastic population models combined with data from long-term forest surveys, we explored whether the climate-sensitivity of recruitment observed in climate manipulation experiments was sufficient to alter populations and elevation ranges of two widely distributed, high-elevation North American conifers. 3. Empirically observed, warming-driven declines in recruitment led to rapid modeled population declines at the low-elevation, “warm edge” of subalpine forest and slow emergence of populations beyond the high-elevation, “cool edge”. Because population declines in the forest occurred much faster than population emergence in the alpine, we observed range contraction for both species. For Engelmann spruce, this contraction was permanent over the modeled time horizon, even in the presence of increased moisture. For limber pine, lower sensitivity to warming may facilitate persistence at low elevations – especially in the presence of increased moisture – and rapid establishment above treeline, and, ultimately, expansion into the alpine. 4. Synthesis. Assuming 21st century warming and no additional moisture, population dynamics in high-elevation forests led to transient range contractions for limber pine and potentially permanent range contractions for Engelmann spruce. Thus, limitations to seedling recruitment with warming can constrain the pace of subalpine tree range shifts.

本数据包包含用于支撑Conlisk等人2017年发表论文《气候变暖下亚高山低海拔种群衰退速率高于高海拔种群增长速率》（Declines in low-elevation subalpine populations outpace growth in high-elevation populations with warming）结论的模型数据。实验数据采集自美国科罗拉多州尼沃特岭（Niwot Ridge）的高山林线增温实验（Alpine Treeline Warming Experiment, ATWE）样地，长期监测样地数据同样采集自该区域，二者被用于构建压缩包"Conlisk_etal_JEcol2017_model_archive12022020.zip"内"Model_archive"文件夹中的模型。该压缩包的内容说明见随附的数据用户指南。压缩包内包含两个文件夹，分别对应论文中的两个物种："EngelmannSpruce"（恩格尔曼云杉）与"LimberPine"（柔枝松）。模型以文本文件形式存储，.sch文件同样可通过文本编辑器打开。需注意，所有文件均专为RAMAS Metapop种群建模软件开发，需使用该程序方可运行这些模型。

"Model_archive"文件夹内包含两份均名为"Conlisk_JofEcology_SI_01262017"的文档：一份为Microsoft Word格式文件，可使用Microsoft Word打开；另一份为PDF格式文件，可通过Adobe Acrobat Reader或其他兼容PDF的软件打开。

1. 气候变化下的物种分布区转移需满足种群补充量超出当前分布边界的条件。对于寿命较长的树木而言，气候敏感型幼苗建成对分布区转移速率的重要性尚未得到定量证实。
2. 本研究结合空间显式随机种群模型与长期森林调查数据，探究了气候控制实验中观测到的气候敏感型种群补充效应，是否足以改变北美两种广泛分布的高海拔针叶树的种群动态与海拔分布范围。
3. 基于观测得到的、由增温驱动的种群补充量下降，模型模拟显示亚高山森林低海拔“暖边缘”处的种群快速衰退，而高海拔“冷边缘”以外区域的种群增长缓慢。由于森林内种群衰退速率远高于高山区域的种群定植速率，两个物种的分布区均出现收缩。对于恩格尔曼云杉，即使在降水增加的情景下，该收缩在模拟时间范围内均为永久性的。而柔枝松对增温的敏感性较低，这使其能够在低海拔区域持续存活——尤其在降水增加的情景下——同时可在林线以上区域快速定植，并最终向高山区域扩张。
4. 综合分析：假设21世纪持续增温且无额外降水补充，高海拔森林的种群动态将导致柔枝松的分布区出现暂时性收缩，而恩格尔曼云杉则可能出现永久性分布区收缩。由此可见，增温背景下幼苗补充的限制因素，会制约亚高山树木分布区转移的速率。