Plant distribution and abundance in relation to physical conditions and location within Danish stream systems
Plant distribution and abundance in relation to physical conditions and location within Danish stream systems
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与丹麦河流系统内的物理条件和位置相关的植物分布和丰度
作者：
T. Riis;K. Sand‐Jensen;S. Larsen
采用单变量和多变量分析方法，研究了河流中专性沉水植物、两栖植物和陆生植物的分布与水深、底质和距岸边距离的关系。这些分析是基于对丹麦小溪主要是小而浅(<；1.6米)的208个无阴影地点的40多个 000样方(25×25厘米)的记录。丹麦河流中的沉水植物包括87个陆生植物，22个两栖植物和30个专性沉水植物。在物理条件中，植物类型的分布主要与水深和距岸边的距离有关，而底层基质的类型对其影响不显著。岸边浅水中以陆生植物和两栖植物(不包括三棱)为主，但随着水深和距离的增加而迅速下降，反映了这些植物之间通过向内生长的方式向水中扩散的重要性。因此，这两类植物在小溪流植物总丰度中所占的比例高于大溪流。这可能反映了该物种从河流系统的上游向下游的纵向扩散，该物种对杂草切割的耐受性以及对低光照下生长的适应。专性沉水植物在中等深度和距离岸边的所有距离处占优势，但0到50厘米除外。这种分布反映了这些物种在溪流中纵向扩散并永久生活在水下的能力。所有物种和专性沉水植物的物种数量在最小的溪流站点比较大的下游站点更低，而陆生和两栖植物的物种数量没有差异。下游沉水物种的增加可以用栖息地面积的增加和植物随水流的扩散来解释，这意味着物种库随着距离源头的距离而积累。这一结果与根据河流连续体概念为中型溪流预测的沉水植物物种最大丰富度不同，该概念是为大型北美溪流开发的，这些溪流上游有森林，下游没有阴影，都不适合沉水植物生长。丹麦溪流的结果表明，流水的纵向联系和与岸上当地物种的横向联系对河流中的植物分布都是重要的。
The distribution of obligate submerged plants, amphibious plants and terrestrial plants in streams was examined in relation to water depth, substrate and distance to the banks using univariate and mulitivariate analyses. The analyses were based on recordings in more than 40 000 quadrats (25×25 cm) in 208 unshaded sites in the predominantly small and shallow (<1.6 m) Danish streams. Also, the distribution of plant abundance and richness from the source to the outlet of the stream system was determined.The submerged plants in Danish streams include 87 terrestrial, 22 amphibious and 30 obligate submerged taxa. The distribution of plant types was mainly related to water depth and distance to the bank among the physical conditions, while the type of bottom substrate had no significant influence. Terrestrial plants and amphibious plants (excluding Sparganium emersum) dominated in shallow water near the bank, but declined rapidly with increasing depth and distance to the bank, reflecting the importance of dispersal by ingrowth from populations on the banks to the water among these plants. Accordingly, these two plant groups constituted a higher proportion of total plant abundance in small streams than large streams. S. emersum dominated on great depth and distance to the banks, probably reflecting the lengthwise dispersal of this species from upstream to downstream parts of the stream system, the tolerance of the species to weed cutting and the adaptation to grow at low light intensities. Obligate submerged plants dominated at intermediate depths and at all distances from the bank except from 0 to 50 cm. This distribution reflects the ability of these species to disperse lengthwise in streams and live permanently submerged.The species number of all species and obligate submerged plants was lower in the smallest stream sites compared to larger downstream sites, while there was no difference for terrestrial and amphibious plants. The downstream increase of submerged species can be explained by the increase of habitat area and the dispersal of plants with the current, implying that the species pool accumulates with distance from the source. This result is at variance with a maximum richness of submerged plant species predicted for intermediate-sized streams according to the River Continuum Concept developed for large North American streams having forested shallow upstream sections and unshaded, deep downstream sections both unsuitable to submerged plant growth. The results for Danish streams imply that both the longitudinal connection through the flowing water and the transversal connection to the local species on the banks are important for plant distribution in the streams.