Department of Ecology, Evolution and Environmental Biology, Columbia University, New York, NY, USA.
Section for Ecoinformatics and Biodiversity, Department of Bisocience, Aarhus University, Aarhus, Denmark.
Glob Chang Biol. 2018 Feb;24(2):e692-e704. doi: 10.1111/gcb.14000. Epub 2017 Dec 22.
Predicting the fate of tropical forests under a changing climate requires understanding species responses to climatic variability and extremes. Seedlings may be particularly vulnerable to climatic stress given low stored resources and undeveloped roots; they also portend the potential effects of climate change on future forest composition. Here we use data for ca. 50,000 tropical seedlings representing 25 woody species to assess (i) the effects of interannual variation in rainfall and solar radiation between 2007 and 2016 on seedling survival over 9 years in a subtropical forest; and (ii) how spatial heterogeneity in three environmental factors-soil moisture, understory light, and conspecific neighborhood density-modulate these responses. Community-wide seedling survival was not sensitive to interannual rainfall variability but interspecific variation in these responses was large, overwhelming the average community response. In contrast, community-wide responses to solar radiation were predominantly positive. Spatial heterogeneity in soil moisture and conspecific density were the predominant and most consistent drivers of seedling survival, with the majority of species exhibiting greater survival at low conspecific densities and positive or nonlinear responses to soil moisture. This environmental heterogeneity modulated impacts of rainfall and solar radiation. Negative conspecific effects were amplified during rainy years and at dry sites, whereas the positive effects of radiation on survival were more pronounced for seedlings existing at high understory light levels. These results demonstrate that environmental heterogeneity is not only the main driver of seedling survival in this forest but also plays a central role in buffering or exacerbating impacts of climate fluctuations on forest regeneration. Since seedlings represent a key bottleneck in the demographic cycle of trees, efforts to predict the long-term effects of a changing climate on tropical forests must take into account this environmental heterogeneity and how its effects on regeneration dynamics play out in long-term stand dynamics.
预测气候变化下热带森林的命运需要了解物种对气候变异性和极端事件的响应。由于幼苗储存的资源较少且根系尚未发育，它们可能特别容易受到气候压力的影响；它们还预示着气候变化对未来森林组成的潜在影响。在这里，我们使用了约 50000 株热带幼苗的数据，这些幼苗代表了 25 个木本物种，以评估：（i）2007 年至 2016 年间年际降雨量和太阳辐射变化对亚热带森林中 9 年幼苗存活率的影响；（ii）三种环境因素（土壤湿度、林下光照和同种邻密度）的空间异质性如何调节这些响应。全社区幼苗存活率对年际降雨变化不敏感，但这些响应的种间变异性很大，超过了平均社区响应。相比之下，全社区对太阳辐射的反应主要是积极的。土壤湿度和同种密度的空间异质性是幼苗存活的主要和最一致的驱动因素，大多数物种在同种密度较低时表现出更高的存活率，对土壤湿度呈正或非线性响应。这种环境异质性调节了降雨和太阳辐射的影响。负的同种效应在多雨年份和干旱地区放大，而辐射对生存的积极影响在林下光照水平较高的幼苗中更为明显。这些结果表明，环境异质性不仅是该森林中幼苗存活的主要驱动因素，而且在缓冲或加剧气候变化对森林更新的影响方面也起着核心作用。由于幼苗是树木生命循环的关键瓶颈，预测气候变化对热带森林的长期影响必须考虑到这种环境异质性，以及它对更新动态的影响如何在长期林分动态中显现出来。
