Boreal plants growing along the southern edge of their range on isolated mountains in a hot desert matrix live near the extreme of their physiological tolerance. Such plants are considered sensitive to small changes in climate. We coupled field observations (1974, 1993, 2019) about the abundance and vigor of small populations of ten remnant boreal plant species persisting in the uppermost elevations of spruce-fir forests of the Chiricahua Mountains, together with modeling of the species sensitivities to three stress factors associated with climatic change: warming, drought, and forest fire, in order to explore the persistence of frontier boreal plant species during climate change. We hypothesize that populations of these cryophilic plants have declined or become locally extinct during an adverse warming period since 1993, enforced by two large forest fires (1994, 2011). We used plant traits and principal component analysis to evaluate sensitivities of the studied plants to the combined actions of warming, drought, and forest fires. Our model predicted selective sensitivity to warming for two species: Vaccinium myrtillus and Rubus parviflorus. Other cryophilic species could be more sensitive to drought and fire. We surveyed the study area in 2019 and found eight of the ten previously investigated species still occur in the area. Five species occurred in wet canyons at lower elevations, but three species persisted in low vigor at the uppermost elevation, which was highly affected by fires. Neither warming-sensitive species showed signs of decline: populations of R. parviflorus increased in abundance and vigor, while V. myrtillus persists without significant changes since 1993. Despite the recorded increase in temperature in the study area >1 °C between years 1975–1993 and 1994–2019, our study did not find direct evidence of warming effects on the observed species. We conclude that severe wildfires and the multi-decadal decrease in precipitation rather than warming are the main limiting factors of remarkable but limited persistence of the remnant boreal species in the Chiricahua Mountains. Our study demonstrates how field observations can be combined with modeling to evaluate species selective responses to different environmental stress factors to make better environmental management decisions, particularly in light of climate change.

在炎热的沙漠基质中，在其山脉南部边缘的偏远山区生长的北方植物生活在其生理耐受力的极值附近。这些植物被认为对气候的微小变化敏感。我们结合了实地观测（1974，1993，2019），考察了奇里卡瓦山云杉杉林最上层持续存在的10种残留北方植物物种的小种群的丰富度和活力，以及对三种胁迫的敏感性模型。与气候变化有关的因素：变暖，干旱和森林火灾，以探索气候变化过程中边境北方植物物种的持久性。我们假设自1993年以来，在不利的变暖时期，这些低温植物的种群数量减少或局部灭绝，由两次大森林火灾（1994，2011）实施。我们使用植物特征和主成分分析来评估所研究植物对变暖，干旱和森林火灾的敏感性。我们的模型预测了两种物种对变暖的选择性敏感性：牛痘菌和小悬钩子。其他低温物种可能对干旱和火灾更为敏感。我们在2019年对研究区域进行了调查，发现先前调查的十个物种中有八个仍存在于该区域中。在低海拔的湿峡谷中发生了五种，但在最高海拔的低势中仍然存在三种，这受到火灾的严重影响。无论是气候变暖敏感的品种表现出下降的迹象：群体R. parviflorus的丰富性和活力增加，而五，欧洲越桔自1993年以来，这一现象一直没有发生明显变化。尽管在1975–1993年至1994–2019年之间，研究区域的温度升高了> 1°C，但是我们的研究没有发现直接变暖对被观察物种的影响的证据。我们得出的结论是，严重的野火和降水减少而不是变暖的年代际减少是奇里卡瓦山残存北方物种的显着但有限的持久性的主要限制因素。我们的研究表明，如何将野外观测与建模相结合，以评估物种对不同环境压力因素的选择性反应，从而做出更好的环境管理决策，尤其是根据气候变化。