During the Halloween-into-Thanksgiving hangover, Verde Valley residents may have noticed encroaching smoke as fire crews carried out prescribed burns along forests in central and northern Arizona.
A 2016 study by the Proceedings of the National Academy of Sciences has found evidence of links between human-caused climate change and wildfires, making controlled burning all the more prevalent. While the smoke impact may be inconvenient and sometimes foreboding, deliberate fires are not only inevitable but necessary.
Firefighters use controlled burning as a preventive tool to keep future wildfires from getting out control as well as improve forest habitat, according to the United States Department of Agriculture.
Burning for Forest Ecology
Ponderosa pine forests and local shrubbery were evolved with fire, according Northern Arizona University fire ecology professor Andrea Thode.
“If they don’t have frequent fire, they get too many trees,” she said. “Too many trees causes it to be a different kind of fire, which is the crown [fire that spreads from treetop to treetop] that rips through the trees and can damage homes and is really not what these ecosystems are designed for.”
In the past, low intensity fires kept forest floors clear of excess fuel buildup like pine needles, leaves and dead grass, resulting in shaping of vegetation patterns today, according to the USDA.
“So if we have prescribed burns, then we can keep the fuel loading down,” Thode said.
Necessity of Controlled Burns
If fires already happen naturally, why is it so important to have controlled burns? According to Thode, it’s because people have historically put them out, disrupting the natural burning process.
“In the late 1800s, grazing heavily came in, which took out all the fine fuels,” she said. “In the early 1900s, we started putting fires out by and 1935, we had a policy to put every fire out by 10 a.m.”
World War II also contributed in fire suppression as the need for lumber was increasing, making fires that destroyed timberland “unacceptable,” according to the United States Forest Service.
“So with the combination of grazing and putting fires out over 100 years, we have a lot of different structure to our forests and we have little trees that carry fire to the big trees,” Thode said. “Fire doesn’t burn the way they would have historically so the idea is to get forests back to a structure so they will burn the way they used to.”
There is a tremendous amount of planning that goes into controlled burning that looks into fire behavior as well as moisture and weather conditions, Thode said.
“They try to make sure the fire burns with low wavelengths,” she said. “They also look at the actual weather that’s coming in at the time to determine how the fire will behave.”
A prescription is then written, like the kind written by a doctor.
“The kind of fire that you want which is low severity surface fire that stays on the ground," Those said.
Fall tends to be prescribed fire season in Arizona because of the ideal weather conditions.
“We generally know that the temperatures are getting colder, which means our relative humidities are getting higher so our fuel typically has a little more moisture even if we haven’t had much rain,” Thode said.
This makes it safer to burn in October and November because of the perfect combination of temperature and moisture.
“The idea is not to do it before fire season,” Thode said. “It’s to prepare for better wildfire, because we are going to have fire whether or not we want it.”
For updated information about controlled burns on the Coconino National Forest, follow @CoconinoNF on Twitter.