There is a similar situation in the Black hills of South Dakota. Just about everywhere you can see small ponderosa pine (or ponderosa like) seedlings encroaching on traditional prairies. Similar causes - vigorous suppression of wildfires. To counter this there are controlled burns and cutting of slash, stacked up on piles awaiting favorable ignition conditions.

Retaining the prairies is important so that the buffalo (and other species) have a place to roam.....