MADERA CANYON - It was a good week to set fire to the grasses and litter on the oak-studded hills that line this canyon in the Santa Rita Mountains south of Tucson.
The grasses were dry enough to burn, the trees moist enough to withstand the flames.
Next month, it might not be such a good idea, with continued drying expected and the wildfire season just around the corner.
Prescribed burns, like the one deliberately set Thursday by the U.S. Forest Service, are protective.
They remove fuel - grasses, shrubs, dead tree branches and other litter that might cause a future fire to burn hotter and to climb into the canopy of the trees, said Scott Smith, assistant fire management officer for the Nogales district of Coronado National Forest.
Setting such fires safely and efficiently is a balancing act that kept wildland fire crews waiting Thursday for a signal from Smith. The weather was "in prescription," but Smith wanted to wait for the sun to warm and the air to dry a bit more before giving the order to light.
A breeze blew at times, helping the crews spread the blaze, but not hard enough to scatter embers beyond the roads and trails containing 137 acres mapped for the fire.
If it had blown too hard, it would have transformed the 40 crew members working the fire from fire-setters to firefighters. The crews included Forest Service and inmate crews from the Arizona State Prison in Tucson, supervised by the Arizona Division of Forestry.
In addition to drip cans of accelerant, the crews carried shovels and swatters to battle any flames that got away.
On Thursday, as they walked in teams across the landscape, nothing got away.
On Friday, the fire continued to smoke, but most of the work had been accomplished. The interior will visibly glow at night for a few days, said the Forest Service's Steve Hensel, who served as safety officer on the fire.
The Kent Springs Prescribed Fire blackened much of the forest floor on the hills east of the paved main road that leads to the picnic and camping areas of Madera Canyon, one of the Coronado National Forest's most visited attractions.
It is difficult to think of this sylvan setting of oak, juniper, running streams and riparian sycamores as an "urban-wildland interface," but that is how Shane Lyman, fire-management officer for the Nogales district of the forest, sees it.
It is one of the places where managing the wildfires that regularly visit the "sky islands" of the Coronado is most difficult.
In addition to managing fire for resource protection, Lyman also has to consider the value of the place's "infrastructure, private homes and developed recreation sites."
Lyman also has to keep an eye on the "interface" with homes in Nogales and Rio Rico and with telescopes atop nearby Mount Hopkins.
Burns such as this one are small in comparison to the wildfires that have been raging across the Coronado in recent years, but they are strategically necessary.
The antidote to the peril of those blazes, the U.S. Forest has decided, is more fire when conditions are right. If you can reduce the fuel load, said Smith, "you reduce the fuel for fires in the future and the overall heat of the forest."
If you can buffer the expensive infrastructure along the forest's boundaries with civilization, you can more easily manage natural fires for benefit of the forest.
The Coronado National Forest covers 1.78 million acres of mountain ranges in southeastern Arizona and southwestern New Mexico.
The sky islands of the Coronado are routinely subject to fire, usually in a season that stretches from April, when things have dried out, to July, when monsoon moisture dampens the possibility of ignition.
This year, things are starting early. Last month's Jelks Fire near Sonoita burned more than 700 acres of grassland. Grasses, which grew well last winter and in summer's monsoon, have dried out since then, said Pete Schwab, fire manager for the Coronado.
"The live-fuel moistures for grass are almost closer to an April time frame," Schwab said. "The critical day for us will be a dry day with a high wind."
Contact reporter Tom Beal at email@example.com or 573-4158.