As wildfires get worse, true toll on scorched lands uncertain
Scientists are troubled by how burned forests in the Southwest aren’t recovering
In the Santa Catalina Mountains north of Tucson, Arizona, soil repels water across the burn scar of the 2020 Bighorn Fire. Steep slopes and an imminent monsoon mean the hydrophobic ground is ripe for erosion.
In the Apache-Sitgreaves National Forests of eastern Arizona, the remnants of salvage logging, thinning operations and prescribed fires mark the areas burned by two of the state’s largest wildfires, the Wallow, in 2011, and Rodeo-Chediski, in 2002. Saplings are seeding near truncated stumps throughout the scorched landscape, hinting at the natural regeneration slowly taking root amid the long-term aftermath of the flames.
In the Chiricahua National Monument in southeastern Arizona, burnt branches are all that is left of once-full squirrel nests. In the decade since the 2011 Horseshoe II Fire was contained, wildlife endemic to the area remain missing. Scientists are searching for signs of life and attempting to understand how vegetation is recovering, in the hopes of being able to predict and prepare for future fires.
Fueled by overzealous fire suppression, drier sum
mers, rising temperatures and a relentless drought, wildfires across Arizona and the Southwest have been sparking more frequently, burning at greater severity and scorching more land.
“What we’re seeing overall is outside the scale of what this landscape has experienced in the past and what it’s capable of accommodating,” said wildlife historian Stephen Pyne. “Ten or even 20 years after the event, we have not seen the recovery that I would have predicted had these fires occurred in the 1960s or 70s. It’s just too dry.”
This fire regime, which has intensified in the past three decades, is transforming the state’s once-dense forests. The long-term effect on plant regrowth, wildlife habitat, watershed health and forest fuels are at the forefront of studies.
“Have you ever played 52card pickup?” asked Don Falk, a professor at the School of Natural Resources and the Environment at the University of Arizona, who is leading research in burn scars across the Catalinas.
In the game, more a practical joke, a dealer throws the deck into the air and instructs players to pick up the cards. Ecology after a megafire is just like it, according to Falk.
“After these big disturbance vents, like wildfires, all the pieces of an ecosystem get thrown up into the air and reorganized, like a deck of cards,” Falk said. “Learning more about what happens when the cards come down is a central question we need to be concerned about. We need to know if these forests are going to recover to what they were or if the cards are going to fall in a way none of us have ever seen.”
As new wildfires spread across tinder-dry Arizona this year, research groups are revisiting the Rodeo-Chediski, Wallow, Horseshoe II, Bighorn, Bush and other burn scars to understand how the ecosystems have been reshuffled.
Fires alter forest floor
Becky Beers steadies each step with her hiking poles as she descends one of the many steep slopes in the Santa Catalina Mountains. As an experiment, and to catch her breath, Beers drops to the ground and brushes aside a thin layer of vegetation litter.
Portions of the soil underneath are still tinged slightly darker by the low-severity flames that burned during the 2020 Bighorn Fire. Whipping out her water dropper, Beers squeezes out a series of droplets. Each sits impeccably beaded on the surface of the soil for minutes before starting to show the slightest sign of sinking into the earth.
“Imagine that but in a highseverity burn area,” Beers said, looking at the droplets. “Imagine that but throughout the entire burn scar.”
Swathes of soil within the Bighorn Fire’s nearly 120,000acre burn scar are now hydrophobic, meaning the soil fails to absorb water. Beers, a research specialist with the Arizona Geological Survey, says this resistance to water can attribute to erosion during the monsoon.
Falk and a research team from the University of Arizona plan to survey approximately 80 study plots across the Catalinas. The plots burned at different severities and a varying number of times in the Bighorn, 2002 Bullock and 2003 Aspen Fires.
“A recovery is a beautiful ecological process,” said Emily Fule, who is leading the study’s field team. “That process is critical to understand because with climate change, the wildfires in these areas are expected to be more common and more severe. If this continues, our research might show the possibility that these forests won’t recover from high-severity wildfires.”
The term “recovery” has an uncertain and complex definition in post-wildfire ecology. Eventually, Falk says, all forests “recover” in one way or another. But that doesn’t mean the ecosystems are anything like what they were before the fire.
Post-fire ecology, compounded by the ongoing drought, is often better suited for invasive plant species that can spread faster than native species.
“If you have a stable ecosystem, native plants can hold their own and repel invaders. But when those places are disturbed by wildfires or erosion, it creates primary succession,” Falk said. “When fire comes through and kills all the native vegetation, everything needs to find its way back. But what’s different this time is that postfire invasive grasses are better suited for these environments. So, by the time natives get there, the invasives have taken root.”
The relationship between grasses and wildfires is what Falk calls a “5-million-year-old love affair.” In essence, wildfires make it easier for grasses to grow and grasses make it easier for wildfires to spread.
Less than 150 miles southeast of the Catalinas are the Chiricahuas.
A decade ago, wide areas of the mountain range, including parts of the Chiricahua National Monument, burned in the Horseshoe II Fire. Over nearly 50 days in 2011, it scorched 223,000 acres.
Andrew Barton, a fire ecologist and biology professor at the University of Maine Farmington, has been conducting research in the Chiricahuas since 1986. On the five-year anniversary of Horseshoe II, Barton helped survey plots of land burned at varying severities.
Now, 10 years after the fire, Barton is back to resurvey the plots.
As part of the research, Barton and his team are studying the sap flow within trees across the burn scar. The researchers hope to understand the relationship between post-fire tree recovery and water.
The research is being funded by NASA, which hopes to see if its ECOsystem Spaceborne
Thermal Radiometer Experiment on Space Station, or ECOSTRESS, instrument can be used to predict the recovery of Southwestern forests.
When it comes to the role humans have in forest recovery, Barton says there are only two potential action plans. First, do nothing and hope forests naturally recover to a healthy state, or second, intervene with the best science available and try to guide recovery.
In the over 35 years he has been doing research in the Chiricahuas, Barton’s opinions have changed.
“When I started coming here, I believed humans should quit intervening with nature,” Barton said. “But now with how extreme climate change is, I don’t see how intervening is any different than what we’ve already done. What we’ve done has been haphazard, maybe now, we could do some good intervening in a more intentional way.”
Barton recalls being stunned by the scale and severity of the 1994 Rattlesnake Fire, which burned 25,000 acres across the Chiricahuas. Less than 20 years later, the Horseshoe II Fire would burn nearly nine times that amount of land.
“If I had only known then,” Barton said.