Despite the dry heat of southern Arizona, the Sonoran Desert has long been surprisingly immune to wildfires. No more, say desert researchers—as invasive species increase in the desert, which stretches from north Phoenix south into Mexico, so does the risk of more frequent, destructive wildfires.
This important work was led by desert ecologist Ben Wilder and colleagues at Northern Arizona University and University of Arizona with the goal of helping land managers throughout the state better prepare for fires and providing information to decision makers as they work toward shared governance for a fire-prone future.
“After the summer of 2020 and the dramatic fires we had across the Sonoran Desert, it became clear that fire was here in the desert as never before,” Wilder said. “Unfortunately, the scientific community had way more questions than answers.”
How the desert has changed
Research released on May 22 by the Southwest Fire Science Consortium showed that, although there have always been occasional desert fires, the Sonoran Desert didn’t have enough fuel to keep flames burning for very long. However, landscape wide expansion of invasive plants in the last two decades, especially when fueled by wet winters has contributed to a new and abundant fuel source that is changing the story. The heat of early summer dries out these plants and leaves them ready to burn. With fire season now beginning, marked by higher temperatures, windy conditions and little precipitation until the monsoon season, those dead plants provide fuel for a fire.
“The Sonoran Desert has largely been fireproof, but that situation is rapidly changing,” Wilder said. “That time period corresponds to when invasive species really began to spread across the larger landscape.”
What to expect in 2024
This spring has been generally wet throughout Arizona, which has land managers concerned. Already firefighters are attacking the Wildcat Fire in the Tonto National Forest, and dry, windy conditions have led to frequent red flag warnings throughout the state.
“There is a lot of fuel on the landscape, much of it invasive, and it is drying out fast,” said Molly McCormick, program manager for the Southwest Fire Science Consortium at NAU’s School of Forestry. “Conditions are ripe for an active fire season.”
It gets even more complicated. Not every fire is the same. The researchers found that different fire regimes emerge in response to different dominant invasive species. In the Phoenix region and Mojave Desert, that main driver is the winter annual red brome and stinknet. Around Tucson, the primary culprits are summer rainfall and the corresponding bunch grasses, buffelgrass and fountain grass.
Phoenix is more likely to see frequent fires as evidenced by the massive 2020 Bush and 2021 Telegraph fires in the Tonto National Forest. Tucson is not far behind as buffelgrass coalesces in patches that span thousands of acres on the front range of the Catalina Mountains. The Bighorn Fire of 2020 did not drop down into the desert for the most part, though researchers say that may not be the case next time.
Looking ahead, what can Arizona do?
The forecast for this season looks grim, but land managers and decision makers at all levels can help Arizona’s deserts and forests become more fireproof.
The report details a developing toolbox of approaches that land managers and decisionmakers can harness to address the rapidly changing situation. Hiking trails and game paths can be used to create larger fuel breaks, taking advantage of the natural patchiness of desert vegetation.
Control of invasive species through mechanical and chemical treatments at small and large scales continues to be important and effective. This is especially the case in trying to protect areas not yet affected by invasive species that can be identified as refugia to be preserved from fires. New wildfire management tactics are also being considered and tested that allow for some degree of prescribed burning in the desert to mitigate the impacts of larger fires.
“It is an all-of-the-above approach,” Wilder says. “There is still time to act, and the cost of action now is far lower and more impactful than it will be in just a couple years.”
The report is freely available online.
