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Park land scorched by Bighorn Fire could offer clues to emerging desert threat

Ben Wilder, director of the University of Arizona’s Desert Laboratory on Tumamoc Hill, stands among saguaros that were severely burned in the Bighorn Wildfire last year at Catalina State Park. Wilder and other researchers have set up scientific 50-by-50-foot plots to study the regrowth of the desert. Already, bright green suckers are growing from the bottoms of blackened mesquites and catclaw acacias.

 Mamta Popat, Arizona Daily Star

On a rocky foothill about a mile from the main road at Catalina State Park, desert ecologist Ben Wilder steps carefully around fresh signs of life in a scorched landscape.

Tiny green shoots of fairy duster dot the ground amid the charred skeletons of mesquites, prickly pears and palo verdes. Some of the burned trees were sawed down by firefighters one year ago last week to slow the spread of the Bighorn Fire.

It’s 8 a.m. Wednesday and already pushing 100 degrees as Wilder hikes to one of 20 new scientific plots set up in the 5,500-acre park to measure the effects of the fire.

Researchers hope to determine what kinds of vegetation fueled the flames and which plants will grow back — or move in — to replace the ones that burned.

One year after the Bighorn Fire, the scars are still easy to see at Catalina State Park, but so are the signs of recovery. Video by Henry Brean/Arizona Daily Star

“The biggest overall question is, how does the desert respond to fire?” says Wilder, director of the University of Arizona’s Desert Laboratory on Tumamoc Hill. “We have really little data about that, because (desert fires) have been such rare events. I don’t really know what to predict, to be honest.”

The vegetation plots were set up last fall, under the direction of ecologist and recent UA graduate Maya Stahl.

Ten of the 50-by-50-foot squares were staked out in patches of desert and grassland burned by the fire. The other 10 were placed nearby, in similar habitat types untouched by the flames.

This summer, the research team plans to install automated sensors at each site to measure temperature, soil moisture and solar intensity.

A burned barrel cactus sits in the 50-by-50-foot study plot set up by Ben Wilder in Catalina State Park.

Then, sometime after monsoon season, they will conduct their first detailed annual survey to count every plant, catalog every species and determine how much of the ground is covered by new growth.

Wilder says they will continue to check on the plots periodically after that, hopefully for decades to come.

“We have to know what’s going on, because this (fire) is likely not a one-off event,” he says.

‘Pretty shocking’

Almost a third of Catalina State Park burned in the lightning-sparked Bighorn Fire, which torched part of a mesquite forest and swept across hillsides speckled with saguaros.

The scars are still obvious a year later, but park manager Steven Haas also sees encouraging signs of the recovery to come.

Along the park’s Birding Trail, bright green suckers grow from the bottoms of blackened mesquites and catclaw acacias. “And some of these saguaros I thought were dead or burned pretty badly are now producing flowers” and fruit, Haas says.

Wilder says it’s “pretty shocking” to see such resiliency, at least so far, from a desert landscape thought to be poorly equipped to survive large-scale fires.

He stops to point out a fishhook barrel cactus he says is “very much alive,” despite its brown, fire-scarred skin. Only the very top of the three-foot cactus is still green, but it continues to produce nectar from tiny red bumps to attract the ants it relies on to control more damaging insects.

Other nearby barrels weren’t so lucky. Those closest to the flames got hot enough to boil their insides, causing them to explode. All that remains a year later are dried husks with holes punched through the sides.

But just a few feet away, native shrubs Wilder thought would be wiped out by the blaze are rebounding instead in unexpectedly high numbers. In some plots, he says, as much as 90% of the limber bush is already growing back.

Even some of the charred palo verdes have begun to re-sprout in their signature spring green.

Weeds and weather

All of this is happening despite one of the hottest, driest stretches of weather ever recorded in Southern Arizona.

“Everything has just been made extra challenging because there has been almost no rain since the fire,” Wilder says. “This is kind of the extreme of the extreme. Hopefully, it doesn’t get worse for these species.”

But it very well could.

The concern among Wilder and others is that once-rare wildfires are becoming a new regime in the Sonoran Desert, as climate change brings rising temperatures and more frequent droughts to a landscape increasingly plagued by invasive weeds like red brome and buffelgrass.

The explosion of buffelgrass in the Catalinas is especially worrisome because the savanna grass from Asia and Africa doesn’t just help fires spread but readily expands into areas scorched by the flames.

Left unchecked, Wilder says, the plant could one day form an unbroken carpet of fuel that not only jeopardizes entire groves of saguaros but allows high-mountain fires to race down into the foothills and lower-elevation fires to climb their way to the summit.

Fire-adapted grass- and shrublands can survive — even thrive — under such conditions. Tucson’s iconic saguaro and palo verde ecosystem might not, Wilder says.

“How much stress can these desert species take? I don’t think they can take multiple fires,” he says.

Ben Wilder, director of the University of Arizona’s Desert Laboratory on Tumamoc Hill, takes a closer look at a palo verde tree that died as a result of the Bighorn Wildfire that burned nearly a third of Catalina State Park.

Lucky firebreak

So why didn’t buffelgrass play a bigger role in the Bighorn Fire?

Dumb luck mostly, according to Jim Malusa, research scientist with the UA School of Natural Resources and the Environment.

After the fire, he, Wilder and others hiked through the lower reaches of the Catalinas to assess the damage. What they discovered — and later documented with 12 fellow researchers in a wide-ranging paper now undergoing scientific review — was a surprising combination of factors that kept the flames away from some of the biggest patches of buffelgrass in Pima Canyon and elsewhere.

“There was enough buffelgrass to make a catastrophic fire, but it never happened,” Malusa says. “It did burn some, but the role of the buffelgrass was very limited.”

The reason: When the fire reached those areas, it was largely burning downhill with little to no wind driving it, so even small breaks in the buffelgrass — a hiking trail or a narrow path tamped down by wildlife — were enough to stop the flames from advancing.

“The next time we might not be so lucky,” Malusa says.

That hints at a possible management strategy: Perhaps some future fire could be stopped in its tracks with a few, well-maintained firebreaks through the worst of the grass. They don’t even have to be very big, Malusa says. “I’m not talking about running a bulldozer over the mountain.”

Buffelgrass is already so widespread that some experts have surrendered hope of ever eliminating it completely from the Catalinas. Wilder, though, thinks $10 million could go a long way toward seriously reducing its threat.

Despite burns from the Bighorn Fire last year, fruit bristles from the arm of a saguaro cactus in Catalina State Park.

If that seems like a lot of money, he says, consider the cost to replace a dozen or so mansions built high in the foothills, right at the wildland’s grassy edge.

“The big takeaway is: The Bighorn Fire was a near miss. A near miss, but a troubling forecast,” Wilder says.

Just add water

Catalina State Park doesn’t have much of a buffelgrass problem, at least not yet, but other invaders can be found there.

During Wednesday’s hike to the vegetation plots, Wilder points out numerous patches of red brome poking up through the native grasses. So far, though, the fire-friendly weed from Europe hasn’t managed to overrun the burn area.

That’s something researchers hope to learn more about as they track the changes to their study plots over the next few years and beyond: After a fire, what comes back, what gets replaced and how long does the process take?

With any luck, Wilder says, the monsoon should provide them with their first set of answers in the coming months.

“What it looks like when we add water, hopefully this summer, will be really telling,” he says. “Just add water and let’s see.”

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Contact reporter Henry Brean at hbrean@tucson.com or 573-4283. On Twitter: @RefriedBrean