Warming‐induced mountain pine beetle (Dendroctonus ponderosae; MPB) outbreaks have caused extensive mortality of whitebark pine (Pinus albicaulis; WBP) throughout the species’ range. In the highest mountains where WBP occur, they cross alpine treeline ecotones (ATEs) where growth forms transition from trees to shrub‐like krummholz, some of which survived recent MPB outbreaks. This observation motivated the hypothesis that ATEs are refugia for WBP because krummholz growth forms escape MPB attack and have the potential to produce viable seed. To test this hypothesis, we surveyed WBP mortality along transects from the ATE edge (locally highest krummholz WBP) downslope into the forest and, to distinguish if survival mechanisms are unique to ATEs, across other forest ecotones (OFEs) from the edge of WBP occurrence into the forest. We replicated this design at 10 randomly selected sites in the U.S. Northern Rocky Mountains. We also surveyed reproduction in a subset of ATE sites. Mortality was nearly absent in upper ATEs (mean ± SE percent dead across all sites of 0.03% ± 0.03% 0–100 m from the edge and 14.1% ± 1.7% 100–500 m from the edge) but was above 20% along OFEs (21.4 ± 5.2% 0–100 m and 32.4 ± 2.7% 100–500 m from the edge). We observed lower reproduction in upper ATEs (16 ± 9.9 cones/ha and 12.9 ± 5.3 viable seeds/cone 0–100 m from the edge) compared to forests below (317.1 ± 64.4 cones/ha and 32.5 ± 2.5 viable seeds/cone 100–500 m from the edge). Uniquely high WBP survival supports the hypothesis that ATEs serve as refugia because krummholz growth forms escape MPB attack. However, low reproduction suggests ATE refugia function over longer time periods. Beyond our WBP system, we propose that plant populations in marginal environments are candidate refugia if distinct phenotypes result in reduced disturbance impacts.

中文翻译：

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高山树线过渡带可能是受到树皮甲虫暴发威胁的山地松树种的潜在避难所

变暖引起的山松甲虫（Dendroctonus藏粉刺; MPB）暴发已导致白皮松（Pinus albicaulis）大量死亡; WBP）在整个物种范围内。在WBP发生的最高山区，它们穿越高山林线过渡带（ATEs），其生长形式从树木过渡到灌木状的krummholz，其中一些在最近的MPB暴发中幸存下来。该观察提出了以下假设：ATE是WBP的避难所，因为Krummholz的生长形式逃脱了MPB的攻击，并具有产生可行种子的潜力。为了检验该假设，我们调查了从ATE边缘（局部最高的Krummholz WBP）下坡到森林的样带的WBP死亡率，并从WBP发生的边缘跨其他森林生态交错带（OFE）来区分ATE的生存机制是否独特。进入森林。我们在美国北洛矶山脉的10个随机选择的地点复制了此设计。我们还调查了ATE站点子集中的繁殖情况。较高的ATE几乎没有死亡率（在边缘0-100m的0.03％±0.03％和边缘100-500m的14.1％±1.7％的所有站点上的平均死亡率为±SE％），但在OFEs上死亡率超过20％ （距离边缘21.4±5.2％0–100 m和32.4±2.7％100–500 m）。与下方的森林（317.1±64.4圆锥/公顷和32.5±2.5可行种子/圆锥100）相比，我们观察到较高的ATE繁殖率较低（16±9.9圆锥/公顷和12.9±5.3可行种子/圆锥从边缘0–100 m）。距边缘– 500 m）。独特的高WBP生存率支持ATE可以作为避难所的假说，因为Krummholz的生长形式逃避了MPB攻击。但是，低繁殖表明较长时期的ATE禁忌症功能。除了我们的WBP系统，我们建议，如果不同的表型导致减少的干扰影响，则边缘环境中的植物种群是候选避难所。