While provision of in‐stream habitat complexity remains common practice in efforts to restore streams, the evidence of positive effects on in‐stream communities is inconsistent. In streams of urban catchments, where both reach‐scale habitat manipulation and catchment‐scale actions to ameliorate the disturbance regime of urban stormwater runoff are common management responses, clearer understanding of the effects of habitat complexity under different degrees of urban impact are needed. We experimentally assessed the effect of increased surface complexity in wood, the dominant hard substrate in our 18 study reaches on 14 small streams, on in‐stream macroinvertebrate assemblages across a range of urban impact. Increased surface complexity increased abundance of most taxa, but this effect was less pronounced in urban streams, partly because of the reduced species pool tolerant of urban stormwater impacts, and partly because of a lesser response of some species to increased complexity in more urban streams. Collectively these taxon‐specific effects resulted in small, uncertain increases in taxon richness with increased complexity in rural streams, and no change in richness of the less diverse assemblages of urban streams. Increased abundances suggest increased availability of refugia or resources with increased surface complexity, while the reduced effect of complexity in urban streams suggests that any refuge or resource provided by greater surface complexity is less effective in more disturbed environments receiving urban stormwater runoff. The reduced abundance of sensitive taxa in more urban streams, and the resultant reduced richness, confirms that urban stormwater runoff acts as a strong environmental filter, limiting the species pool available for community assembly. Restoration of habitat complexity in streams without catchment‐scale drivers of degradation is likely to have positive benefits to in‐stream biotic assemblages, but the efficacy of such approaches in catchments subject to urban stormwater runoff will be greatly diminished. In such cases, restoration activities should first be aimed at controlling the larger‐scale problem.

中文翻译：

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流域规模的城市化减少了栖息地复杂性对上游无脊椎动物群落的影响。

尽管提供河内栖息地复杂性在恢复河川的努力中仍是惯例，但对河内社区产生积极影响的证据却不一致。在城市集水区，常见的管理对策包括达到规模规模的栖息地操纵和改善城市雨水径流扰动机制的集水规模行动，因此需要对不同程度的城市影响下的栖息地复杂性的影响有更清晰的认识。我们通过实验评估了木材表面复杂性增加的影响，在我们的18项研究中，占主导地位的硬质基材覆盖了14条小溪流，对整个城市影响范围内的溪流大型无脊椎动物群落。增加的表面复杂性会增加大多数分类单元的丰度，但这种影响在城市溪流中不那么明显，部分原因是由于减少了对城市雨水影响的物种库容忍度，部分是由于某些物种对更多城市溪流中复杂性增加的反应较小。这些特定于分类单元的效应共同导致分类单元丰富度的不确定性小幅增加，而农村河流的复杂性也随之增加，而城市河流的多样性较少的人群的丰富度没有变化。丰度的增加表明，避难所或资源的可利用性随着地表复杂性的增加而增加，而城市河流复杂性的降低的影响表明，由更大地表复杂性提供的任何避难所或资源在受到城市雨水径流影响的环境中效率较低。在更多的城市河流中，敏感分类单元的数量减少，从而导致其丰富度降低，证实了城市雨水径流是一种强大的环境过滤器，限制了可供社区聚集的物种库。在没有集水规模的退化驱动因素的情况下，恢复河流生境复杂性可能会对河流中的生物群落产生积极的好处，但是这种方法在遭受城市雨水径流的集水区的功效将大大降低。在这种情况下，恢复活动应首先针对控制更大范围的问题。但是这种方法在遭受城市雨水径流的流域的效力将大大降低。在这种情况下，恢复活动应首先针对控制更大范围的问题。但是这种方法在遭受城市雨水径流的流域的效力将大大降低。在这种情况下，恢复活动应首先针对控制更大范围的问题。