Fuel for the Fire

Christmas Day, I flew from Tucson to Peoria, IL. The plane was a smaller regional plane with two seats on each side. Next to me was a tall man close to my age. We chatted about why we were going to Peoria (hometown for both of us) and where we were coming from (southwest Texas for him, Tucson for me, of course). But he had lived in Tucson for twenty years before he was transferred to Texas. It turns out he is a National Park firefighter!

The Bighorn Fire

He’d fought the Bighorn fire over Pusch Ridge in Tucson in 2020. This fire was the first that had me thinking about evacuating. At first, I assumed that Oracle Road was wide enough to act as a fire break, but watching the wind whip the flames around, I realized I should have an evacuation plan.

  The firefighter said that the Bighorn was an interesting fire to fight, and they’d had some difficult times. I’m still amazed they managed to save all the threatened human-made structures. Fortunately, he told me that it turned out that most of the fire was of low and moderate intensity. Low-intensity fires occur occasionally in the desert. Fires had been infrequent and localized, so the native plants did not develop fire resistance.

With the desert’s low humidity and violent monsoon storms with lightning, fires are common. However, the plant coverage of the ground is patchy, so fires are limited in area. At least they were limited before the proliferation of invasive species.

Invasive Fuel

With the introduction of invasive species, such as buffelgrass (Pennisetum ciliare, Cenchrus ciliaris), fires today have too much fuel and are in danger of burning at too high a temperature. This results in fires that destroy keystone species, such as saguaro cactus (Carnegiea gigantea). 

Buffelgrass

Recently, more extensive, hotter fires have increased in frequency. Unfortunately, many of the fires result from direct human action or the presence of human-introduced plants. These plants fuel the fires, which are not present in the natural environment. Complicating the situation is that the invasive plants tend to recover faster after the fire is out, outcompeting the native plants yet again.

An average forest fire burns at 1,472° F, with flames less than five feet tall. But a fire with more fuel and enhancing conditions can burn almost twice as hot, at 2,192° F, with flames reaching 150 feet. The hotter fires severely damage the Sonoran desert environment, often permanently damaging it.

With the hotter fires, increased destruction of the saguaros has occurred. The plants can be killed outright, despite their high water content, or they may be fatally injured. The hotter the fire, the higher the saguaro mortality or death rate. In addition, the fire destroys other desert plants, resulting in erosion during rains.

Saguaros need protective shading by nurse plants to grow. Consequently, the nurse plants must regrow first, providing the required habitat conditions for the iconic cactus.

Notice how the saguaro is growing underneath the palo verde ‘nurse’ tree.

Watching the Bighorn fire, I was surprised to hear that the damage was not as bad as I had feared. However, I am relieved that this lightning-ignited fire didn’t permanently destroy the unique desert ecosystem.

Native plants an animals are an important part in conserving all of our unique ecosystems, and my educational workbooks are a great way to learn more about native habitats and their inhabitants!