Resistance to Movement

Greater Sage-Grouse

We modeled resistance to movement by sage grouse following the methods described in an empirical model that used landscape genetics approaches to determine resistance weights (Shirk et al. 2015). This model predicts high resistance to movement arising from barriers like interstate highways, cities, large transmission lines, and forests, with more moderate resistance coming from primary and secondary roads, agricultural lands, and areas of warmer or cooler climate relative to the mid to higher elevations of the Columbia Basin.

Dry (Xeric) Shrubsteppe Ecosystem

We modeled resistance across the xeric ecosystems using an expert-based approach. The human footprint data layer was the primary driver of resistance, with higher costs to movement modeled as a linear increasing function of the human footprint. Additional resistance was added for movement over water, forested areas, and cliffs (but these areas were not considered total barriers). So, areas with low human footprint in a natural vegetation type (except forest, water or cliff) were considered optimal for movement.

Wet (Mesic) Shrubsteppe Ecosystem

Resistance across the mesic ecosystem was also driven largely by the human footprint, but additional resistance was also added as 1) an increasing function of the height above nearest drainage, 2) a decreasing function of the normalized difference wetness index (NDWI), and cliffs. So areas with low human footprint in low-lying areas with moist vegetation and no cliffs were considered optimal for movement.