Mike mentioned forest fire burns. That is one of the fascinating aspects of the road from the Yellowstone south entrance down to Jackson Hole. When we were there two years ago , it was only a month or so after a major fire had closed the road for days. We drove through a patchwork of burned areas and areas the fire had skipped over. There were even rows of trees that were geen on one side and brown on the other. Trees don't grow fast in that climate so you will still see the effects of the fire well.
There are exhibits along the road with amps and the history of fires in northwest Wyoming. Something like 80 % of the land has had one or more fires in the last 200 years, most of them natural. Old brush clearnace by fire seems to be an important part of the ecosystem.