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首页> 外文期刊>Oecologia >Responses of floodplain forest species to spatially condensed gradients: a test of the flood-shade tolerance tradeoff hypothesis
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Responses of floodplain forest species to spatially condensed gradients: a test of the flood-shade tolerance tradeoff hypothesis

机译：漫滩森林物种对空间凝结梯度的响应：洪水阴影容忍权衡假设的检验

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Previous work in southeastern US floodplains led to the hypothesis that a tradeoff between flood and shade tolerance underlies species-specific responses to flooding and light, which drive forest regeneration. In systems where community turnover can occur with small-scale environmental changes, testing this hypothesis requires recognizing that turnover of species along the two gradients can be large relative to the spatial distances involved. We test the tradeoff hypothesis in an old-growth bottomland hardwood forest by (1) comparing shade and moisture profiles of woody juveniles versus random points and (2) using individual-based sampling of woody juveniles to model probability of occurrence in response to distance-to-water table and canopy openness gradients. We found that juveniles of all species combined occupied a similar range of distance-to-water table compared to measurements taken at random points, but average canopy openness above seedlings was significantly higher than at random points. On average, shade-tolerant species, with the exception of Acer rubrum, were found in shaded areas that were also drier, whereas less shade-tolerant taxa, plus A. rubrum, were found in wetter, more open areas, suggesting a tradeoff between flood and shade tolerance. Predictive models of species occurrence, which incorporate the availability of canopy and microtopographic conditions, indicated that three taxa (Fraxinus pennsylvanica, Quercus spp., and Ulmus americana) had patterns consistent with a flood-shade tolerance tradeoff. In contrast, Asimina triloba, Celtis laevigata, and Liquidambar styraciflua had positive responses when the joint stresses of flooding and shade were diminished. A. rubrum appeared to be the most tolerant to both stresses. Our work not only lends support to the flood-shade tradeoff hypothesis but also indicates that a more general model is needed that includes a '' flood-shade release '' component. We also suggest that responses to small-scale gradients should not be overlooked, particularly in systems where the gradients are ecologically steep.
机译：美国东南部漫滩的先前工作得出这样的假设，即在洪水和阴凉容忍度之间进行权衡是对洪水和光照的特定物种响应的基础，后者推动了森林的更新。在小规模环境变化可能导致社区更替发生的系统中，要验证该假设，就必须认识到，沿着两个梯度的物种更替相对于所涉及的空间距离可能很大。我们通过（1）比较木质幼体与随机点的阴影和水分分布，以及（2）使用基于个体的木质幼体采样来模拟响应距离的发生概率，来测试在古老的矮林硬木森林中的权衡假设地下水位和树冠开放度梯度。我们发现，与在随机点进行的测量相比，所有物种的幼体到水位的距离范围相似，但幼苗上方的平均冠层开放度显着高于随机点。平均而言，在较干燥的阴影区域中发现了除枫叶槭以外的耐荫树种，而在较湿润，更开放的区域中发现了不耐荫的分类单元和红曲菌，这表明在耐水和阴凉。物种发生的预测模型，结合了冠层和微地形条件的可用性，表明三个分类群（Fraxinus pennsylvanica，Quercus spp。和Ulmus americana）的模式与洪水遮蔽容忍度折衷相一致。相比之下，当淹没和遮荫的共同压力减小时，三叶草（Asimina triloba），小叶芹（Celtis laevigata）和枫香（Liquidambar styraciflua）表现出积极的反应。红曲菌似乎对两种压力都最宽容。我们的工作不仅支持洪水阴影权衡假设，而且表明需要一个更通用的模型，其中包括“洪水阴影释放”组件。我们还建议不要忽视对小尺度梯度的响应，尤其是在梯度在生态学上陡峭的系统中。

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