Abstract Nurse tree canopies mitigate exposure to freezing temperatures that could result in injury or mortality to the saguaro cactus (Carnegiea gigantea). Abiotic objects have been hypothesized to provide similar beneficial microclimates. We used data loggers at 11 nurse rock sites to record daily daytime summer maximum and winter nighttime minimum temperatures at Saguaro National Park, Arizona, to examine the effectiveness of rocks to moderate seasonal temperature extremes in the microclimate. Temperatures at rock sites averaged 2 °C warmer than exposed open control sites in winter. We found that the efficiency of rocks to act as insulators significantly increased as temperature at control sites decreased, consistent with studies of tree canopies, and that the insulation effect lasted throughout the night. In summer, rocks reduced exposure to maximum temperatures but did not offer significantly more cooling at higher temperatures. Our results suggest that the protection from freezing temperature offered by rocks in winter is more ecologically beneficial to the saguaro than extreme temperature amelioration during summer in the cold-limited frontiers of the species’ range.

中文翻译：

---

护士岩微气候显着缓冲了冰冻温度和温和的夏季温度

摘要 护士树冠层可减轻冰冻温度的影响，冰冻温度可能导致仙人掌 (Carnegiea gigantea) 受伤或死亡。已经假设非生物物体提供类似的有益微气候。我们在 11 个护士岩石站点使用数据记录器记录亚利桑那州仙人掌国家公园的每日白天夏季最高温度和冬季夜间最低温度，以检查岩石对缓和小气候中季节性极端温度的有效性。冬季，岩石地点的温度比裸露的开放对照地点平均高 2°C。我们发现，随着控制点温度的降低，岩石作为绝缘体的效率显着提高，这与树冠的研究一致，并且绝缘效果持续了一整夜。在夏天，岩石减少了对最高温度的暴露，但在更高的温度下并没有提供更多的冷却。我们的研究结果表明，与夏季在物种范围的寒冷限制边界上的极端温度改善相比，岩石在冬季提供的免受冰冻温度的保护对仙人掌更具生态效益。