I agree with their 'shifting mosaic' description. But I hesitate to apply historical observations to older times. My view is bison were nomadic, migratory, or sedentary at various places and times, depending on fire, predation, snow cover, drought, topography, etc. and their interactions.

This paper has a nice multi-proxy analysis of fire, vegetation, moisture availability, and a possible herbivore indicator w/ spike moss. doi.org/10.1016/j.qu...