The importance of trimming National Hydrography Dataset streamline networks when delineating potential habitats and species distributions for fish and amphibians in broad geographical applications.

The article focuses on evaluating and improving the accuracy of the National Hydrography Dataset (NHD) streamline networks in representing potential habitats and species distributions of fish and amphibians across broad geographic scales in the northwestern USA. Using large occurrence data sets for ten species linked to medium-resolution NHD-PlusV2 stream reaches, the study found that many species rarely occupy headwater reaches characterized by the smallest flows and steepest slopes, which constitute a large portion of the NHD network. Applying species-specific habitat thresholds based on reach slope and mean flow substantially reduced the estimated stream lengths likely occupied by native species, indicating that untrimmed NHD networks often overestimate habitat extents. The authors suggest that trimming NHD networks using available reach attribute descriptors can enhance the accuracy of species range estimates, sampling designs, and predictive models, while noting that the choice to customize networks depends on project goals and available data.