Scale effects of riparian forests on fish diversity in streams of the upper Paraná River basin

Despite the ecological importance of riparian forests to streams, the specific scale at which forest cover most significantly influences fish assemblages remains poorly understood. To address this issue, we measured the percentage of forest cover at 11 spatial scales across 12 streams. These scales were categorized into: “local riparian”, which includes circular buffers around the sampled sections, and “riparian network”, which consists of buffers surrounding the stream network upstream of the sampled sections. We developed linear models using species diversity, based on Hill numbers, and the percentage of forest cover at each scale. Additionally, we included the terrain slope and the dominant type of land use in the watershed (rural or urban) as covariates. The results indicated that the 100-m buffer of the local riparian scale was the most effective for assessing fish diversity. The percentage of forest cover in this buffer had a positive and significant relationship with the diversity metrics, though terrain slope significantly influenced this relationship. Therefore, we recommend that studies evaluating the influence of landscape on fish assemblages in streams adopt a multiscale approach to avoid missing the true impact of the landscape on the assemblages.