Fuel in uncut stands is mostly on the surface beneath tree canopies, which limits fire spread between trees. A single fire can reduce Mexican pinyon sapling density tenfold. Low-severity surface fires at 50 or 60 year intervals will thin Mexican pinyon, preventing development of thickets. Fire intervals greater than 80 years result in dense stands of Mexican pinyon and a build up of fuel. In narrow canyons, Mexican pinyon crowns can overlap both with one another and with herbaceous vegetation on slopes.
Small fires can easily become crown fires.