Evaluation of the use of landscape classifications for the prediction of freshwater biota: synthesis and recommendations

This paper summarizes and synthesizes the collective results that emerged f rom the series of papers published in this issue of J-NABS, and places thes e results in the context of previously published literature describing vari ation in aquatic biota at landscape spatial scales. Classifications based o n landscape spatial scales are used or are being evaluated for use in sever al countries for aquatic bioassessment programs. Evaluation of the strength of classification of different approaches should provide insight for refin ement of existing bioassessment programs and expedite the development of ne w programs. The papers in this series specifically addressed the degree to which descriptions and classification of landscape features allow us to acc ount for, and thus predict, variation in the composition of biota among ind ividual sites. In general, we found that although landscape classifications accounted for more biotic variation than would be expected by chance, the amount of variation related to landscape features was not large. Thus, larg e-scale regionalizations, if used alone to specify expected biotic conditio ns, will likely have limited use in aquatic bioassesments, where it is crit ical to specify expected conditions as accurately and precisely as possible . Landscape classifications can play an important additional role, however, by providing an initial stratification of site locations to ensure that di fferent landscape features are adequately represented in a sampling program . In general, we believe a tiered classification based on both reach-level and larger-scale landscape features is needed to accurately predict the com position of freshwater fauna. One potential approach entails use of landsca pe classifications as a means of refining or augmenting classifications bas ed on local habitat features, which appear to account for substantially mor e biotic variation than larger-scale environmental features. These results have significant implications for how assessment and monitoring programs at local, state/province, and national levels should be designed.