U.S. Geological Survey, Fort Collins Science Center, Fort Collins, Colorado, USA.
Under Contract to U.S. Geological Survey, Fort Collins Science Center, Fort Collins, Colorado, USA.
Ecol Appl. 2022 Dec;32(8):e2689. doi: 10.1002/eap.2689. Epub 2022 Aug 7.
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.
现在，人们对河水的需求不断增加，这与维护河岸生态系统的愿望不断增加相冲突。为了有效地管理河流流量以维持河岸植被，需要了解流量影响的时间尺度，但由于缺乏长期研究植被对流量变化的响应，这方面的信息有限。为了研究短期和长期流量变化以及大坝运行对河岸植被的影响，我们在 1990 年至 2013 年期间的五次不同时间，在科罗拉多州 Gunnison 河的 133 个已知淹没排放率的永久性样地中，确定了 107 种植物的出现。个别物种随着平均年流量的增减而在淹没排放率的梯度上上下移动，当流量与植被采样前的时间加权相关时，流量与物种出现的相关性最强，其中位数半衰期为 1.5 年。然而，一些高大的、根茎状的、多年生物种对流量的响应时间更长。70 种物种的出现与淹没持续时间之间存在显著的对数回归关系。随着低淹没持续时间的干涸和高淹没持续时间的河流干扰，样地物种丰富度和总植被覆盖率下降。随着淹没持续时间的增加，年内样地间物种出现的相似性显著下降。中等淹没持续时间以高大的、根茎状的、多年生草本植物为主，包括入侵的 Phalaris arundinacea（芦竹）。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，这与假设一致，即由于流量调节导致流量峰值降低和低流量增加，减少了依赖干扰的物种的建立机会。总的来说，植被的年际变化受到流量变化的强烈影响，而十年来的变化则受到上游流量调节引起的河流干扰减少的影响，这种变化在本研究开始前几十年就已经开始。
