Raster Overlay Techniques to Identify Bighorn Sheep Habitat

Raster Overlay Techniques to Identify Bighorn Sheep Habitat Christopher Gran

Bighorn Sheep Analysis in Glacier National Park Purpose: Utilize Geographic Information Science (GIS) to assist the U. S National Park Service (NPS) in identifying areas of suitable habitat for bighorn sheep in Glacier National Park. NPS wildlife managers are interested in analyzing the location and interactions of the following three criteria that have been identified as desirable for bighorn sheep habitat: § Criterion 1: Bighorn sheep use precipitous topography (escape terrain) to evade predators and reduce predation of their neonates. This terrain is composed of slopes between 27 -85 degrees. § Criterion 2: Bighorns are primarily animals of open and semi-open habitats like alpine meadows, open grassland, and rock outcrops. These are favored characteristics because they must have optimal view of their surroundings in order to survive. Dense forests provide poor visibility making it difficult for sheep to detect predators. § Criterion 3: Bighorn sheep habitat is also characterized by low human disturbances. Requisite data to meet NPS habitat conditions: § § § Study area location: Glacier National Park, Montana Soil composition - To select rock outcrops and shallow soils. Vegetation cover - To classify dispersed low herbaceous vegetation. Park elevation - For identifying escape terrain between 27 – 85 degrees. Roads and trails - To set an appropriate buffer zone from human disturbance. Park boundary 1

Applicable spatial data files were obtained from the NPS data store and the Vegetation Mapping Project site of the NPS (Table 1). Table 1 Layer File Coordinate System Soils soils. shp NAD_1983_UTM_Zone_12 N Vegetation glacveg. shp NAD_1983_UTM_Zone_12 N Elevation (10 meter) dem 10_c NAD_1983_UTM_Zone_12 N Roads roads_rev 2008. shp NAD_1983_UTM_Zone_12 N Trails trails_public. shp NAD_1983_UTM_Zone_12 N Park Boundary boundary 2003. shp NAD_1983_UTM_Zone_12 N Data Preparation for Boolean Overlay For Boolean overlay analysis, each layer file was prepped to symbolize only suitable habitat attributes (Figure 1). Shapefiles were converted to rasters with a 100 meter cell resolution and cells with suitable habitat were attributed with a value of 1. The digital elevation raster was reclassified to assign a value of 1 for slopes between 27 and 85 degrees. Boolean overlay adding the rasters illustrates how many factors are present in a location while Boolean overlay multiplying renders only the areas where all preferred attributes are present. Figure 1 2

Table 2 Weighted Raster Overlay Weighted overlay analysis was implemented by reclassifying all layers into a 1 through 10 scale of suitability by the values listed in Table 2. Values are determined by the distance from preferential habitat – close proximity to suitable terrain and remoteness from human disturbance have highest values. The weighted sum tool provides an integrated analysis by multiplying raster layers according to their designated suitability weights, then sums the weighted rasters (Figure 2). The resulting raster’s continuous values are broken into 5 classes and appropriately symbolized to illustrate bighorn sheep habitat suitability on a scale of 1 through 10. Figure 2 3

Weighted Raster Overlay N Esc_Suit Rock_Suit Low. Veg_Suit Hum_Suitability Range 1. 0 – 2. 6 2. 7 – 4. 4 4. 5 – 6. 2 6. 3 – 7. 7 7. 8 - 10 4

Data Sources Administrative Boundary for Glacier National Park, Montana (2003) [downloaded file]. Glacier National Park GIS Program. URL: https: //irma. nps. gov/Data. Store/Reference/Profile/1042581 (June 2016). Hiking Trails in Glacier National Park, Montana (2014) [downloaded file]. Glacier National Park. URL: https: //irma. nps. gov/Data. Store/Reference/Profile/2206913 (June 2016). Glacier National Park, 10 -meter Digital Elevation Model (2001) [downloaded file]. Glacier National Park GIS Program. URL: https: //irma. nps. gov/Data. Store/Reference/Profile/1034478 (June 2016). Glacier National Parks, Lakes (1990) [downloaded file]. Glacier National Park GIS Program. URL: https: //irma. nps. gov/Data. Store/Reference/Profile/1019882 (July, 2016). Public Roads in Glacier National Park (2014) [downloaded file]. Glacier National Park GIS Program. URL: https: //irma. nps. gov/Data. Store/Reference/Profile/2218512 (June 2016). Soils of Glacier National Park (2001) [downloaded file]. Land & Water Consulting, Missoula MT. URL: https: //irma. nps. gov/Data. Store/Reference/Profile/2171240 (June 2016). Spatial Vegetation Data for Glacier National Park Vegetation Mapping Project (2007) [downloaded file]. U. S. Geological Survey-National Park Service Vegetation Mapping Program, Denver , CO. URL: https: //catalog. data. gov/dataset/spatial-vegetation-data-for-glacier-national-park-vegetation-mapping-project (June 2016). 5