Origins of abrupt change? Postfire subalpine conifer regeneration declines nonlinearly with warming and drying
Origins of abrupt change? Postfire subalpine conifer regeneration declines nonlinearly with warming and drying
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DOI：
10.1002/ecm.1340
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发表时间：
2019-02-01
影响因子：
6.1
通讯作者：
Turner, Monica G.
中科院分区：
文献类型：
--
作者：
Hansen, Winslow D.;Turner, Monica G.
高强度森林火灾后树木的强劲更新是亚高山和北方森林恢复力的关键，如果火灾后的温度和土壤湿度变得不适合树苗的建立，21世纪的气候可能会引发森林的突变。我们利用两种广泛分布的针叶松（Pinus contorta var. latifolia）和Douglas-fir （Pseudotsuga menziesii var. glauca）进行了互补实验，以了解(1)21世纪早期到中期的预计增温和干燥将如何影响火灾后树木的幼苗建立和死亡率？(2)不同树种间早苗生长有何差异？通过4年的原位种子种植试验和1个生长季节的控制环境试验，探讨了气候对树木幼苗建立、生长和存活的影响，并确定了温度和土壤湿度对树木幼苗的非线性响应。在我们的现场试验中，与21世纪中期的预测一致，温暖和干燥的条件导致黑松和道格拉斯冷杉的种植减少了92%和76%。在三年内，所有在温暖条件下生长的幼苗都死亡了，正如在物种分布范围的低海拔和低纬度地区所预料的那样。幼苗的成活率和死亡率也随树形的不同而不同；近1.7倍多的幼苗在旱生方面建立和较少的幼苗死亡。在控制环境试验中，土壤温度比田间试验低2.0 ~ 5.5℃，升温导致树苗成活率增加，这在高树线或高纬度地区是可以预料到的。随着气候变暖，洛奇波勒松比道格拉斯冷杉长得更高，并且产生了更多的针叶。与黑松相比，道格拉斯冷杉的根比芽长，特别是在干燥的土壤中。物种间早期生长差异可能调节气候变化对竞争相互作用、演替轨迹和物种分布的影响。研究表明，高烈度火灾后的气候对亚高山针叶林火灾后的树木更新具有很强的控制作用。气候变化实验，如这里所报道的，在确定21世纪生态系统中可能支持根本生态变化的机制方面具有巨大潜力。
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 degrees-5.5 degrees 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.