Identifying natural catchment landscape influences on tropical stream organisms: classifying stream reaches of the Hawaiian Islands

Stream classifications can be used to understand patterns within and across river networks and are most informative when they offer insight into patterns in stream habitat or biology. We developed a classification of Hawaiian stream reaches based on influences of natural landscape features on distributions of stream organisms to understand patterns in ecological potential across five Hawaiian Islands. Our objectives were to (1) identify natural landscape variables strongly associated with species distributions and likely to affect stream habitat; and (2) classify Hawaiian stream reaches based on relationships between landscape variables and distributions of native stream taxa. We used canonical correspondence analysis to identify natural landscape variables associated with distributions of nine native stream taxa. To classify reaches, we then used a conditional inference tree that identified significant influences of natural landscape variables on taxa distributions and showed that elevation, channel slope, hydrologic soil grouping, and rainfall were all important predictors of species distributions. Results were used to develop reach classes that describe differences in stream habitat. Our research adds to current understanding of landscape controls on the biota of tropical island streams and provides a tool for decision makers tasked with developing conservation and adaptation strategies.