Quantification of flooding thresholds that govern species distributions on microtopographic gradients in floodplains can help design environmental flows, but the multiple correlated dimensions of flooding such as frequency, depth, duration, and timing are a challenge. We postulated that species distributions are limited by the most stressful combination of flooding dimensions when the plants are in their most susceptible developmental stage. To test this idea, we measured survival of young seedlings in pots subjected to flood treatments that completely submerged the seedlings in stagnant water with and without suspended sediments for durations of up to 6 weeks during the growing season. This measure of flood tolerance predicted floodplain distributional limits of 16 tree species with high accuracy (adj. r² = 0.91). The strength of the result suggests that seedling ability to survive complete submergence in stagnant water for prolonged periods is an important mechanism limiting species distributions in riparian forests. We propose that environmental flows that completely submerge the seedling layer in floodplain forest with stagnant water for at least 3 weeks are likely to be more effective at eliminating invading upland species than flows that only flood the soil up to the root collars of seedlings.

洪泛阈值控制洪泛平原上微地形梯度上的物种分布，可以帮助设计环境流量，但是洪水的多个相关维度（例如频率，深度，持续时间和时间安排）是一个挑战。我们推测，当植物处于其最易感的发育阶段时，物种分布受到最大洪水压力组合的限制。为了检验这一想法，我们测量了经过洪水处理的盆中幼苗的存活情况，该盆将幼苗完全浸没在有或没有悬浮沉积物的死水中，在整个生长季节中长达6周。这项抗洪能力的测量方法可以高精度地预测16种树种的洪泛区分布极限（调整r ² = 0.91）。结果的强度表明，幼苗能够长时间完全滞留在积水中，这是限制沿岸森林物种分布的重要机制。我们认为，在积水淹没的洪泛区森林中至少三周内完全淹没幼苗层的环境流，比仅将土壤淹没到幼苗的根环上的流，可能更有效地消除了入侵的旱地物种。