Watershed Ecological GroupsBackground: Key drivers in the function and formation of wetland and riparian ecosystems include climate, hydrology, geology, and soils (Brinson 1993, Smith 1995). Wetland and riparian ecosystems occurring in similar landscape or watershed settings reflect similar climatic, hydrologic, geologic, and soil influences (Winters et al. 2006). As a result, they typically have common emergent properties, including vegetation and functions (Brinson 1993, Johnson 2005). This allows for the profiling, or characterization of watersheds according to the abundance and diversity of specific hydrologic and geomorphic settings present (Spivey and Ainslie 2004, Johnson 2005, Winters et al. 2006, Lemly et al. 2011). Applied to landscape-scale assessment, monitoring, and restoration, a watershed’s profile can be compared to that of reference watersheds having the same profile (Tiner 2002, Johnson 2005, Winters et al. 2006). Making comparisons between watersheds first requires classification of watersheds into similar ecological groups based on environmental characteristics (Johnson 2005 Winters et al. 2006, Lemly et al. 2011). Classification of watersheds can be based on multivariate analysis of spatially-derived attributes (Johnson 2005, Winters et al. 2006, Lemly et al. 2011). Watershed profiling—Classification of HUC 12 / watershed ecological groups: The widely used hierarchical classification of watersheds mapped by the U. S. Geological Survey (Seaber et al. 1987) was chosen for classification of ecological groups. This classification aggregates watersheds or parts of watersheds into coded hydrologic units. As in similar watershed-scale analyses (Johnson 2005, Winters et al. 2006, Lemly et al. 2011), twelve-digit (6thlevel) hydrologic units (HUC 12s) were used. For this analysis, we classified all HUC 12s within the state of Idaho. Multivariate analysis techniques performed in PC-ORD version 4.25 (McCune and Mefford 1999, McCune and Grace 2002) were used to classify and ordinate HUC 12s into ecological groups according to their mapped soil, climatic, hydrologic, and geomorphic characteristics (Johnson 2005, Winters et al. 2006, Lemly et al. 2011). The following factors were assumed to represent the hydrologic and geomorphic settings for each HUC 12: aspect (north, 315 - 45 degrees)elevation (classified) heat load (classes) HUC 12 area (relativized 0 - 100)lithologic units (Quigley et al. 1999) precipitation (DAYMET) (mean annual classified) slope (classified) soil units (STATSGO)stream order (by segment)temperature (DAYMET) (mean annual classified)topographic positions (classes)GIS analysis of available spatial layers for the above factors was used to calculate the percent of each HUC 12 represented by each factor. This ensured that no factor was weighted in the multivariate analysis more heavily than another. To reduce noise in the dataset, any factors occurring in only one HUC 12 were dropped. Potential groups were derived by hierarchical, polythetic, agglomerative cluster analysis using Relative Sorenson (Bray-Curtis) distance measure and the flexible beta linkage method (flexible beta = -0.250, to minimize chaining) (PC-ORD v. 4.25, McCune and Mefford 1999). Watershed ecological groups were identified by subjectively “pruning” the dendrogram at the point where maximum information (indicated by longer limbs on the dendrogram) was captured by the fewest number of groups. Relationships between groups were examined by Bray-Curtis ordination (PC-ORD v. 4.25, McCune and Mefford 1999). Bray-Curtis ordination used a Relative Sorenson distance measure and endpoints were selected using variance-regression. The final watershed ecological groups were then given descriptive names for labeling in this shapefile.Ecological ZonesEcological zones represent Level IV Omernik Ecoregions classified by relative elevation and ecological characteristics. Ecoregions denote areas of general similarity in ecosystems and in the type, quality, and quantity of environmental resources. They are designed to serve as a spatial framework for the research, assessment, management, and monitoring of ecosystems and ecosystem components. These general purpose regions are critical for structuring and implementing ecosystem management strategies across federal agencies, state agencies, and nongovernmental organizations that are responsible for different types of resources within the same geographical areas. The approach used to compile this map is based on the premise that ecological regions can be identified through the analysis of patterns of biotic and abiotic phenomena, including geology, physiography, vegetation, climate, soils, land use, wildlife, and hydrology. The relative importance of each characteristic varies from one ecological region to another. A Roman numeral hierarchical scheme has been adopted for different levels for ecological regions. Level IV ecoregions are further subdivisions of Level III ecoregions. Methods used to define the ecoregions are explained in Omernik (1995, 2004), Omernik and others (2000), and Gallant and others (1989).
