Data from: Effects of riparian forest harvest on streams: a meta-analysis

1. Riparian forest harvesting impacts streams in many ways, from altering temperature regimes, shifting geomorphic structure, increasing sediment fluxes and affecting fish populations. However, we have noted considerable variation in the results between studies that led us to ask whether the effects of forest harvesting on streams were consistent between studies. We used meta-analysis of 34 replicated studies to address the effects of riparian logging on biological and chemical components of streams in contrast to control sites. 2. We found that the overall effect sizes of several response variables in replicated studies were significantly higher than zero, especially benthic invertebrates, and nitrogen and potassium concentrations. However, there was a very large amount of variation in the effect sizes between studies, and for many measures, the effect sizes from different studies were positive or negative, indicating site-specific responses. 3. We explored whether stream size, stream gradient and regional potential evapotranspiration could explain some of the effect size variation between studies. Relations with these environmental variables were weak, but suggestive that some of the context-specific, individual outcomes might be due to underlying environmental differences between sites. 4. Synthesis and applications. Despite relatively low numbers of replicated studies, we found significant overall effects of riparian forest harvesting although the magnitude and direction of responses within individual studies were site specific. This lack of consistency in the direction of effect sizes suggests we need a more context-dependent approach to the protection of freshwaters from forest management.1. 河岸林（riparian forest）采伐可通过多种途径对溪流造成影响，涵盖改变水温格局、重塑地貌结构、增加泥沙通量以及影响鱼类种群等方面。但现有研究的结果存在显著异质性，这促使我们探究：森林采伐对溪流的影响在不同研究间是否具有一致性？本研究基于34项重复研究开展元分析（meta-analysis），旨在对比对照样地，明确河岸林采伐对溪流生物与化学组分的影响。 2. 本研究发现，在重复研究中，多项响应变量的总体效应量（effect size）显著大于0，其中尤以底栖无脊椎动物（benthic invertebrates）、氮浓度与钾浓度最为明显。但不同研究间的效应量仍存在极大异质性；针对多数观测指标而言，不同研究得到的效应量可正可负，这表明溪流响应存在位点特异性。 3. 本研究探究了溪流规模、溪流坡度以及区域潜在蒸散发（potential evapotranspiration）是否能够解释部分研究间的效应量异质性。结果显示，这些环境变量与效应量的相关性较弱，但仍暗示部分位点特异性的个体研究结果差异，可能源于样地间潜在的环境差异。 4. 综合与应用。尽管本研究纳入的重复研究数量相对有限，但仍明确了河岸林采伐对溪流存在显著的总体影响；不过单个研究中溪流响应的强度与方向均具有位点特异性。效应量方向缺乏一致性这一结果表明，在通过森林管理保护淡水水体时，我们需要采用更具情境依赖性的研究与管理策略。