The Great Basin is characterized by strong patterns of precipitation along approximate north-south gradients (Miller and others, 2013). Hence, we used a hydrographic boundary layer developed by Mason (1999), to divide the region-wide extent of sage-grouse habitat mapping analysis into North and South regions that align coarsely with respective mesic (wet) and xeric (dry) regions of the state. Flood regions are based largely on patterns of snowmelt, summer thunderstorms or cyclonic rainfall, and the 8-digit Watershed Boundary Dataset (WBD, 2015) was used to select appropriate watersheds within our mapping extent that corresponded to the Mason (1999) boundary. Slight adjustments, made in ArcMap 10.3, included joining region 2 and 3 to comprise the majority of the North region (where a relatively low number of sampled sites precluded keeping regions 2 and 3 separate), and pooling the more xeric Owyhee Desert (located in the center of the northern part of Nevada) within the drier South region.
Use of the hydrographic boundary allowed for an accounting of broad-scale variation in habitat availability and selection patterns for sage-grouse (for example, habitat classified as highly suitable in wet areas could be classified as less suitable in drier areas because these habitats are less available). Interim statewide habitat suitability maps were clipped by the hydrographic boundary and relativized according to their respective maximum values for map classification purposes (see Coates and others 2014), the independent set of sage-grouse telemetry points was also split by the hydrographic boundary. For the spring map, 837 points informed the North region while 794 informed the South region. For the summer map, 604 points informed the North and 794 the South. For winter, 326 informed the North and 411 the South. For our composite annual map made from the multiplicative product of the seasonal maps, 1767 points were used for the North and 1999 for the South.
References:
Coates, P.S., Casazza, M.L., Brussee, B.E., Ricca, M.A., Gustafson, K.B., Overton, C.T., Sanchez-Chopitea, E., Kroger, T., Mauch, K., Niell, L., Howe, K., Gardner, S., Espinosa, S., and Delehanty, D.J. 2014, Spatially explicit modeling of greater sage-grouse (Centrocercus urophasianus) habitat in Nevada and northeastern California—A decision-support tool for management: U.S. Geological Survey Open-File Report 2014-1163, 83 p., http://dx.doi.org/10.3133/ofr20141163. ISSN 2331-1258 (online)
Mason, R.R. 1999. The National Flood-Frequency Program—Methods For Estimating Flood Magnitude And Frequency In Rural Areas In Nevada U.S. Geological Survey Fact Sheet 123-98 September, 1999, Prepared by Robert R. Mason, Jr. and Kernell G. Ries III, of the U.S. Geological Survey; and Jeffrey N. King and Wilbert O. Thomas, Jr., of Michael Baker, Jr., Inc. http://pubs.usgs.gov/fs/fs-123-98/
Miller RF, Chambers JC, Pyke DA, Pierson FB, Williams CJ. 2013. A review of fire effects on vegetation and soils in the Great Basin Region: response and ecological site characteristics. Gen. Tech. Rep. RMRS-GTR-308. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. http://www.fs.fed.us/rm/pubs/rmrs_gtr308.html.
WBD, 2015. Coordinated effort between the United States Department of Agriculture-Natural Resources Conservation Service (USDA-NRCS), the United States Geological Survey (USGS), and the Environmental Protection Agency (EPA). The Watershed Boundary Dataset (WBD) was created from a variety of sources from each state and aggregated into a standard national layer for use in strategic planning and accountability. Watershed Boundary Dataset for {HUC#8}, Nevada_ST.zip [ftp://rockyftp.cr.usgs.gov/vdelivery/Datasets/Staged/Hydro/FileGDB101/]. Available URL: http://datagateway.nrcs.usda.gov [Accessed 01/10/2015].
