Table 2. Information for each landscape variable tested including resistance level(s), hypothesis and corresponding predictions.

Landscape Variable	High/low resistance	Hypothesis	Prediction(s)
Null	Uniform landscape	Isolation by Distance	No effect of landscape on gene flow
Land cover	Forest = low	Isolation by Resistance	Gaps in woodland (e.g., grassland/ treeless canyons) restrict movement and gene flow.
	Non-forest = high
Elevation	< 1500 m = low	Isolation by Resistance	High elevations are a barrier to gene flow
	> 1500 m = high
Land-elevation	Combined land cover and elevation resistance maps	Isolation by Resistance	1. Variation in elevation in combination with changes in forest composition (i.e. deciduous to coniferous) restricts gene flow
			2. Denser forests at high elevation facilitate gene flow
Hybrid	Pure zone = low	Isolation by Resistance	Poplar hybrid zones attract chickadees and thereby inhibit further gene flow
	Hybrid zone = high