Increasing demand for river water now conflicts with an increasing desire to maintain riparian ecosystems. Efficiently managing river flows for riparian vegetation requires an understanding of the time scale of flow effects, but this information is limited by the absence of long-term studies of vegetation change in response to flow variation. To investigate the influence of short- and long-term flow variability and dam operation on riparian vegetation, we determined the occurrence of 107 plant species in 133 permanent plots of known inundating discharge along the Gunnison River in Colorado on five different occasions between 1990 and 2013. Individual species moved up and down the gradient of inundating discharge coincident with increases and decreases in mean annual flow, and the correlations between flow and species occurrence were strongest when flows were weighted by time before vegetation sampling with a median half-life of 1.5 years. Some tall, rhizomatous, perennial species, however, responded to flows on a longer time scale. Logistic regression of species occurrence showed a significant relation with inundation duration for 70 out of 107 species. Plot species richness and total vegetative cover decreased in association with desiccation at low inundation durations and with fluvial disturbance at high inundation durations. Within-plot similarity in species occurrence between years decreased strongly with increasing inundation duration. Moderate inundation durations were dominated by tall, rhizomatous, perennial herbs, including invasive Phalaris arundinacea (reed canary grass). Over the 23-year study period, species richness declined, and the proportion of rhizomatous perennials increased, consistent with the hypothesis that decreases in flow peaks and increases in low flows caused by flow regulation have decreased establishment opportunities for disturbance-dependent species. In summary, annual-scale changes in vegetation were strongly influenced by flow variation, and decadal-scale changes were influenced by decreases in fluvial disturbance from upstream flow regulation beginning decades prior to the onset of this study.

中文翻译：

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河岸植被对短期和长期水文变化的响应

现在对河水的需求不断增加与维护河岸生态系统的愿望越来越强烈相冲突。有效管理河岸植被的河流流量需要了解流量影响的时间尺度，但由于缺乏对植被变化响应流量变化的长期研究，该信息受到限制。为了研究短期和长期流量变化和大坝运行对河岸植被的影响，我们在 1990 年至 2013 年的五个不同时间确定了科罗拉多州甘尼森河沿岸 133 个已知淹没流量永久性地块中 107 种植物的出现情况. 个别物种随着年平均流量的增加和减少而在淹没流量的梯度上下移动，当流量在半衰期中值为 1.5 年的植被采样之前按时间加权时，流量与物种出现之间的相关性最强。然而，一些高大的、根茎状的多年生物种在更长的时间尺度上对流量做出反应。物种发生的逻辑回归显示 107 个物种中的 70 个与淹没持续时间显着相关。地块物种丰富度和总植被覆盖率下降与低淹没持续时间的干燥和高淹没持续时间的河流扰动有关。随着淹没持续时间的增加，地块内物种发生的年份之间的相似性急剧下降。中度淹没持续时间以高大、根状茎、多年生草本植物为主，包括侵入性植物 物种发生的逻辑回归显示 107 个物种中的 70 个与淹没持续时间显着相关。地块物种丰富度和总植被覆盖率下降与低淹没持续时间的干燥和高淹没持续时间的河流扰动有关。随着淹没持续时间的增加，地块内物种发生的年份之间的相似性急剧下降。中度淹没持续时间以高大、根状茎、多年生草本植物为主，包括侵入性植物 物种发生的逻辑回归显示 107 个物种中的 70 个与淹没持续时间显着相关。地块物种丰富度和总植被覆盖率下降与低淹没持续时间的干燥和高淹没持续时间的河流扰动有关。随着淹没持续时间的增加，地块内物种发生的年份之间的相似性急剧下降。中度淹没持续时间以高大、根状茎、多年生草本植物为主，包括侵入性植物 随着淹没持续时间的增加，地块内物种发生的年份之间的相似性急剧下降。中度淹没持续时间以高大、根状茎、多年生草本植物为主，包括侵入性植物 随着淹没持续时间的增加，地块内物种发生的年份之间的相似性急剧下降。中度淹没持续时间以高大、根状茎、多年生草本植物为主，包括侵入性植物Phalaris arundinacea（芦苇金丝雀草）。在 23 年的研究期间，物种丰富度下降，根茎多年生植物的比例增加，这与流量调节导致的流量峰值减少和低流量增加减少了依赖干扰的物种的建立机会的假设一致。总之，植被的年度尺度变化受流量变化的强烈影响，而年代际尺度的变化则受到本研究开始前几十年开始的上游流量调节河流扰动减少的影响。