The U.S. Forest Service has put together information about how previous fuel treatments modified fire behavior on the San Juan Fire on the Apache-Sitgreaves National Forest in Arizona in June of 2014. Below is an excerpt from a report, and below that is a video in which subject matter experts describe the effects of the treatments.
Generally speaking, the fuel treatments encountered by the San Juan Fire were effective at modifying fire behavior. Furthermore, these fuel treatment areas proved to be instrumental in providing fire managers with opportunities to contain the fire in a safe and effective manner while simultaneously limiting the fire’s potential negative effects on natural resources, the surrounding communities and their infrastructure.
Fire behavior observed by firefighters at the scene—as well as estimates of fire severity taken after the fire confirm that the treated areas performed as designed by not supporting sustained crown fire even under extreme burning conditions.
As the San Juan Fire transitioned from untreated mixed conifer to treated ponderosa pine, fire behavior also transitioned from intermittent and sustained high-intensity crown fire in the untreated stands to a low-moderate intensity surface fire in the treated stands.
Thus, firefighters were able to utilize the road system within the treated stands to implement their burnouts. These burnout operations limited the forward progress at the head of the fire the day after the fire started.
This may be true under most fire weather conditions, but not the extreme conditions, which is when most big, hot fires occur. All bets are off.