Saguaro Land is a series from The Show looking at the Sonoran Desert — the lushest, hottest desert in the world that happens to be our home.
Arizona and the West have been dealing with longer wildfire seasons and more severe fires over the past several years. But Mary Lata says fire in the Sonoran Desert is becoming more common.
Lata is the fire ecologist for the Tonto National Forest, which is just shy of 3,000,000 acres. Of that, about 850,000 acres is in the Sonoran Desert, while on the northern end there are about 350,000 acres of ponderosa pine and mixed conifer forests. In between, there’s chaparral and woodlands.
Lata says fire moves across the landscape based on the vegetation, and that while some systems tend to burn quickly — think grasslands — others burn more slowly, but with high severity.
Lata spoke with The Show about how fire impacts the Sonoran Desert with The Show.
Full conversation
MARY LATA: In Ponderosa pine and timbered systems, there are trees that record fire. There are fire scars on the trees and we can go and see them and know for a fact when fire burned through these areas in many cases. In the Sonoran Desert, there's no way really for us to really know how often fire burned through that area. We have to make assumptions based on the response of the areas to fire when it does burn, on the way fire moves around when it does burn.
People always ask about Saguaro, of course. It can handle a little bit of fire. A large, mature Saguaro can handle a little bit of fire; it can’t handle the big hot flame lengths. But if you go up to a large Saguaro, you'll notice that the bottom two to three feet of the main stem is kind of a corky bark-looking thing; it's not green. And if it's just grass burning underneath it and it goes by pretty quickly, it'll probably be okay. But when the other shrubs that are around it—if it's growing in a group or a clump of vegetation—if they all burn too, then it's likely going to kill it.
MARK BRODIE: I'm curious about the role of introduced species and maybe if they play more of a role with fire in the Sonoran Desert than they do in other places, or maybe it's not any different than it is elsewhere?
MARY LATA: Yes, introduced species play a significant role. They come in at a time of year and spatially spread out in a way that most of the desert species don't. And they have two main roles in regards to the plants in the desert — one is that they compete with the natives, and two is that they provide fuel to let fire move around in the desert in ways that historically it's unlikely that it did.
MARK BRODIE: Is that something that is maybe unique to this part of the world, to the Sonoran Desert relative to other places?
MARY LATA: Well, I don't know how unique it is in terms of there being introduced species, but it is having a really significant effect on the Sonoran Desert. The introduced species, particularly buffelgrass, which is the big bad one in the southern Sonoran Desert, and red brome, which is the big bad one in the northern Sonoran Desert, are destabilizing these systems based largely on fire and also on competition.
MARK BRODIE: So you mentioned how challenging it is to really get a handle on the history of fire in the Sonoran Desert. Is it possible to sort of project what the future might look like, though, in terms of areas and severity and size of wildfires on the Sonoran Desert?
MARY LATA: Well, funny you should ask that. There are a lot of people right now trying to figure out what the ecological future of the Sonoran Desert actually is. What we're seeing is where fire has burned in the desert, it's much more likely to come back with a much higher cover of grass. Most systems in this world that have a lot of grass burn a lot. So we have a positive feedback loop going on where it burns and then it comes back with more grass, which makes it more flammable, so it's more likely to burn, and so on. We don't know how to short-circuit that.
MARK BRODIE: So what does that mean then for the future of the desert and some of the plants that live here and the people who live here and sort of the general ecosystem?
MARY LATA: Well, if people want an ecosystem to be stable and not change, then they'll need a different planet, but that—I know that sounds harsh. The changes that are happening right now in the Sonoran Desert are happening really fast. The Sonoran Desert that was here 50 years ago, and certainly 100 years ago, is gone. The breadth and spread of these introduced species is such that we cannot get rid of them. Now, that doesn't mean we're going to lose a bunch of species; it means that the desert is going to kind of change its face. It will become patchier. There are some places that fire cannot burn because it's too rocky, and fortunately for us, those tend to be, amongst other things, places where Saguaros really love to grow. So Saguaros may end up retreating into those areas, but we're not going to lose it.
MARK BRODIE: So do these changes seem to be aesthetic? Are they more than that for the Sonoran Desert?
MARY LATA: Um, I think they're more than aesthetic, although they are certainly that as well. Those of us who are tasked with managing large areas of the Sonoran Desert are trying really hard to figure out what management actions are going to be supportive of whatever the ecological future of the Sonoran Desert is. But right now, we're not sure what that is.
MARK BRODIE: Does it seem as though fire is changing the Sonoran Desert more than it's actually changing other areas?
MARY LATA: It sure seems like that to me. It takes a long time for a Saguaro, for example, to become mature, and when fire goes through, it has a much bigger impact on the young Saguaro than it does on the old. I mean, it does that to Ponderosa pine too, but pine has a lot of other adaptations for fire, and Saguaro doesn't have a lot.
MARK BRODIE: Yeah, I was going to ask in what ways, and it sounds as though, as you referenced, the Saguaro is sort of the symbol of the Sonoran Desert and, as you just mentioned, like, it doesn't have a lot of adaptations, a lot of ways to sort of deal with fire; it either kind of survives it or it doesn't, and those seem to be the two options.
MARY LATA: Yeah, I mean, there's a gentleman by the name of Ben Wilder who's done some research down in Southern Arizona and he's come up with a phrase we call "grassification," which is what we're all seeing. If you drive up Highway 87 and look at where the Bush Fire burned, it's really obvious, or over where the Telegraph Fire burned, it's really obvious. The Sonoran Desert is turning into more of a grassland system, but we don't really know what the whole thing will look like. We know there will be patches where the desert vegetation is not impacted by fire, but big, big areas of it will be and they will become more grass-dominated.
MARK BRODIE: So you mentioned planning for the future, and I'm wondering what some of the unknowns are that you're trying to figure out as you're planning for the future and trying to figure out what that future might look like, what it might entail.
MARY LATA: One of the things that's a little harder to understand is the impact of fire on soil. Desert soils are really fragile, and so any kind of mechanical disturbance—be that people or wheels or hooves or anything that disturbs it mechanically—is going to leave it pretty vulnerable. We don't know as much about the impacts of heat, especially long-term, on the desert soil. And as far as longer-term changes, there isn't a ton of data out there yet that shows us what direction the vegetation might go if it starts burning a lot.
MARK BRODIE: As there's more and more fire in the Sonoran Desert, what are you looking for to see maybe how it behaves similarly or differently than it behaves in other ecosystems, or what kind of effects it has here relative to other ecosystems?
MARY LATA: Part of it's the response. What we are seeing is a system that was really young anyway; ecologically it's only about 10,000 years old, which means it was a little unstable anyway. It had components of species like mesquite or acacia that are really well adapted for fire, and then it has a whole suite of species such as small cacti that are not particularly well adapted to fire, and they were still kind of figuring it out. So now we added introduced species and they are letting fire in there, and trying to understand exactly what the signature is going to be is a challenge.
MARK BRODIE: All right. That is Mary Lata, the fire ecologist on the Tonto National Forest. Mary, thank you so much for the conversation. I appreciate it.
MARY LATA: Thanks, Mark.
-
The Show's Amy Silverman reflects on the Saguaro Land series, and the plight of the iconic Sonoran Desert cactus that is its namesake. -
The Show is exploring the desert season by season in the series Saguaro Land — through music, art, literature, food, drink, flora and fauna — and now through design. -
Journalist Caroline Tracey has watched as Instagram and other platforms have turned a spotlight on the desert in ways she finds both refreshing — and troubling. She spoke to The Show more about the trend and what it means. -
In The Show's newest installment of Saguaro Land, we learned about using the desert to make music from Kyle Bert, who has been turning agave stalk into didgeridoos for 25 years. -
Tempe artist Safwat Saleem used baking as a metaphor for describing how he and his young daughter are learning to thrive in the Sonoran Desert.
