Spatiotemporal patterns of landscape characteristics are important drivers of the distributions of fish and wildlife. Landscape characteristics such as land use, land cover, and disturbance within riparian areas may have both direct and indirect effects (e.g., through impacts on water quantity, quality, and temperature) on the ecology and distributions of aquatic species. Quantification of these landsape-scale watershed components across large geographic extents is greatly enhanced by remote sensing technologies. To better understand the influence of landscape characteristics on the distribution of brook trout (Salvelinus fontinalis) within part of its native range in Minnesota’s Lake Superior basin, we used the random forest algorithm to model species occurrence. We obtained watershed-level attributes from the 2016 National Land Cover Database, Landsat time series-based forest canopy disturbance data (1974-2018), the Forest Inventory and Analysis database, delineations of land ownership and protection status, and combined these with electrofishing data and historical stocking records. We created variable-width riparian buffers for watersheds within Minnesota’s Lake Superior basin using the Riparian Buffer Delineation Model, assessed landscape characteristics within and outside riparian areas at multiple hydrologic unit code (HUC) scales, and applied these data to our random forest analysis of brook trout occurrence.
Results/Conclusions
Land cover in the study area’s 12-digit HUC watersheds (HUC12s) is 82% forested, with 15% disturbed at least once (1974-2018). Variable-width riparian buffers comprise ~17% of the total area and are 89.9% forested, with 9.7% disturbance, as compared to 16% disturbance in non-riparian forested lands. Overall, 57% of disturbance was timber harvest, followed by flood (33%), wind (8%), conversion (1%), fire (1%), and other (<1%). Timber harvest was the most frequent disturbance agent over all land ownerships, and occurred most frequently on state-owned forest. Conversion occurred most frequently on private lands, whereas fire and wind disturbance were most frequent on federal lands. Brook trout were recorded in 44% of 174 surveyed HUC12s. Preliminary results from random forest analysis shows that percentages of developed and forested cover within riparian areas are more important for distinguishing occupied watersheds than those cover types across the watershed as a whole. These cover types are more important than agricultural cover, perhaps due to the scarcity of agriculture in this region. These results emphasize the critical role of terrestrial management within riparian areas for fish ecology. This application of landscape ecology offers a strategic approach for incorporating terrestrial characteristics into watershed management and conservation planning.