Robust tree regeneration following high‐severity wildfire is key to the resilience of subalpine and boreal forests, and 21st century climate could initiate abrupt change in forests if postfire temperature and soil moisture become less suitable for tree seedling establishment. Using two widespread conifer species, lodgepole pine (Pinus contorta var. latifolia) and Douglas‐fir (Pseudotsuga menziesii var. glauca), we conducted complementary experiments to ask (1) How will projected early‐ to mid‐21st‐century warming and drying affect postfire tree seedling establishment and mortality? (2) How does early seedling growth differ between species and vary with warming and drying? With a four‐year in situ seed‐planting experiment and a one growing season controlled‐environment experiment, we explored effects of climate on tree seedling establishment, growth, and survival and identified nonlinear responses to temperature and soil moisture. In our field experiment, warmer and drier conditions, consistent with mid‐21^st‐century projections, led to a 92% and 76% reduction in establishment of lodgepole pine and Douglas‐fir. Within three years, all seedlings that established under warmer conditions died, as might be expected at lower elevations and lower latitudes of species’ ranges. Seedling establishment and mortality also varied with aspect; approximately 1.7 times more seedlings established on mesic vs. xeric aspects, and fewer seedlings died. In the controlled‐environment experiment, soil temperatures were 2.0°–5.5°C cooler than the field experiment, and warming led to increased tree seedling establishment, as might be expected at upper treeline or higher latitudes. Lodgepole pine grew taller than Douglas‐fir and produced more needles with warming. Douglas‐fir grew longer roots relative to shoots, compared with lodgepole pine, particularly in dry soils. Differences in early growth between species may mediate climate change effects on competitive interactions, successional trajectories, and species distributions. This study demonstrates that climate following high‐severity fire exerts strong control over postfire tree regeneration in subalpine conifer forests. Climate change experiments, such as those reported here, hold great potential for identifying mechanisms that could underpin fundamental ecological change in 21st‐century ecosystems.

中文翻译：

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突变的起源？火后亚高山针叶树的更新随着变暖和干燥而非线性下降

高强度野火后健壮的树木再生是亚高山和北方森林恢复力的关键，如果篝火后的温度和土壤湿度变得不适合用于树苗的建立，那么21世纪的气候可能会引发森林的突然变化。使用两个普遍的针叶树种，黑松（松扭叶松变种宽叶）和花旗松（花旗松变种青冈），我们进行了补充实验以询问（1）预计21世纪初至21世纪中叶的变暖和干燥将如何影响火后树苗的形成和死亡率？（2）物种之间的幼苗早期生长如何不同，并且随着变暖和干燥而变化？通过一项为期四年的原地种子种植实验和一个生长季节控制环境实验，我们探索了气候对树木幼苗的建立，生长和存活的影响，并确定了对温度和土壤湿度的非线性响应。在我们的野外实验中，温暖和干燥的条件与^21st中旬一致几个世纪以来的预测使黑松和花旗松的建立分别减少了92％和76％。在三年之内，所有在温暖条件下建立的幼苗都死亡了，这可能是在物种范围的较低海拔和较低纬度下所预期的。苗木的建立和死亡率也随方面而变化；在中耕和干旱方面建立的幼苗大约增加了1.7倍，并且死亡的幼苗更少。在受控环境试验中，土壤温度比田间试验低2.0°-5.5°C，变暖导致树苗生长的增加，这可能是在较高的林线或较高纬度地区所预期的。小枝松比道格拉斯冷杉长得更高，并且随着变暖而产生更多的针叶。与黑毛松相比，花旗松相对于枝条的根系更长，特别是在干燥的土壤中。物种之间早期生长的差异可能会介导气候变化对竞争相互作用，演替轨迹和物种分布的影响。这项研究表明，高强度火后的气候对亚高山针叶林的火后树再生有很强的控制作用。气候变化实验（如此处报道的实验）具有巨大的潜力，可用于确定可能支撑21世纪生态系统基本生态变化的机制。