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How the changing landscape of the Sonoran Desert has made it more at risk for wildfires

The Sonoran Desert has, in the past, generally been immune from wildfire. But new research says that’s starting to change. Ben Wilder, a Tucson-based desert ecologist, botanist and biogeographer, says a handful of fires that happened this year prove the point: the Wildcat Fire northeast of Scottsdale burned more than 14,000 acres; the Simmons Fire, Adams Fire and Spring Fire are also among those which are or have burned in the Sonoran Desert recently.

Wilder is the director of Next Generation Sonoran Desert Researchers. The Show spoke with him about what this new research has found.

Full conversation

BEN WILDER: Well, you know, again, being born and raised in the desert and I've grown up very much thinking that the desert pretty much fireproof, and looking back at the record largely supports that. So one of the main reasons, that has been is that there's just a lot of open space in the desert. You know, we can all when you go out for a hike, you can kind of move around the shrubs, try to avoid the cactus. And there's generally a lot of open space, which means that fires really won't get carried there's not that fuel, that would carry fires.

The exception to that is after wet winters. You know, when we have a great wildflower displays, when those flowers and that biomass dries down, that then can definitely carry a fire and has, but just occasional in these wet years and generally not very hot and not very large areas, but invasive species are completely changing that story to making the desert fire prone Now.

MARK BRODIE: Yeah, how much of that is because of invasive species and how much might be other factors that are making the Sonoran Desert more fire prone.

WILDER: Now, the the primary mechanism and cause are invasive species. They are the, they're the that that kind of game changer where you have the, they're creating the fuels that carry the fire. There are commingled factors here. Other other elements at play, one of them is increased ignition sources though that in B and vis species love roadways and they're dried down at this time of year and they're essentially waiting there to get sparked and caught.

And then you also of course, have many more ignition sources in our public lands from shooting ranges to perhaps some less cautious approaches to recreating that unfortunately are having dramatic impacts and actually some of the causes for some of the biggest fires that we've seen and also the, the long term drought that the Greater Southwest is in is also a factor here.

BRODIE: Right. Well, so when you talk about those invasive species, like, are these things that, that just got here on their own or any of these like? Are, are we the cause of any of these?

WILDER: Yes, that's a good question. The there's two really main types that we, that in, in, in conducting the study, we saw. One, these are grasses or small herbs, but one set is really connected to winter rainfall. These are red brome, annual grass stinknet, an annual composite and sunflower family that are rapidly expanding, especially around the Phoenix area and have rapidly expanded and can create these blankets of fuel.

The second set are species and more bunch grasses that are responded to summer rains. This is buffle grass or fountaingrass or lehmann lovegrass. Their present in Phoenix a bit more common actually in the Tucson region that's a little more accelerated what's happened in the Phoenix region and accordingly, that's why the fires seem to be, be worse thus far in in the Phoenix region.

BRODIE: So assuming then that there will be more fires in the Sonoran Desert, both in the Phoenix area, the Tucson area. What does that mean for the ecology of these areas?

WILDER: A significant amount of change. One of the, the term we're using for this change is grassification and essentially what that means is you have these grass species which were intentionally brought in for the most for the most part for erosion control, some were accidentally brought in by people as well and they respond actively to fire. In other words, they be, they be are benefited from fire. They rose strongly after fire. They're from ecosystems that fire is a part of. Whereas the desert for a large part really, it did not evolve with fire. So native Sonoran Desert species can tolerate fire to some extent we're finding what's been sprouting but certainly not repeated burns. But then these non-native, these invasives grow stronger.

So to succinctly say where this grassification is burning the native vegetation, these grasses that are evolved with fire come back stronger and replace our native desert species and essentially transform the desert into a grassland.

BRODIE: Well, so it sounds like if your assumptions are correct and the invasive species really start to take over and respond to fire the way that they have so far, it almost sounds like the, the very nature of what the Sonoran Desert is and what it looks like and sort of what vegetation is there that seems like it's gonna completely change.

WILDER: The the implications are, are pretty staggering When you, when you pull it out. However, I think it's important that we're at a turning point, meaning that there, if we let things go, if things continue unchecked and these are large scale processes. Then yeah, that is, this is where we can expect things to go, but there's a lot that can be done right now. Fire is not rampant across the landscape everywhere. It's expanding.

We outline a lot of management actions that can be taken especially in the wildland urban interface, right? You know, where cities are meeting a now flammable desert. And you know, there's a lot of nuance, it's a huge landscape. There are small scale topographical differences, meaning, you know, changes in elevation and the desert is not going to be uniformly responding to this. However, areas that do burn because of invasive species, the response is very clear and it, it's, it's a full scale transformation of that ecosystem that does burn.

BRODIE: Well, So you mentioned the wildland urban interface and I have to ask, you know, if the Sonoran Desert is more fire prone, there's some two pretty big population centers encompassed in that in terms of the Phoenix and the Tucson areas. Does that put cities more at risk? Does that put those of us who live in those cities more at risk?

WILDER: Yes. It, it does there, there's so we've been able to do live in a landscape here in the desert where, you know, fire is not really one of the things that we consider certainly relative to forest environment where you have forest fires and that's just part of your mindset and the maintaining defensible space, right? We don't even think about that in the desert. That's changing.

However, one of the main goals of this point of the, of this report is that there's time to act, right? This is this is the trends and rates of change we see in process that we can still reduce the fuel loads. I mean, we know the cause of invasive species. OK, let's remove the invasive species where we can, especially in these defensible spaces around our, our homes and businesses and areas of, of societal importance.

And we also know that the inherent patchiness that bare ground of the desert limits fire. So let's use that to our strength when we think about building field breaks and defensible spaces. 

BRODIE: All right, Ben, thank you so much for the conversation. I really appreciate it.

WILDER: Thank you.

BRODIE: Ben Wilder is a Tucson-based desert ecologist, botanist and bio geographer. He's also director of next generation Sonoran Desert researchers.

KJZZ's The Show transcripts are created on deadline. This text may not be in its final form. The authoritative record of KJZZ's programming is the audio record.

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Mark Brodie is a co-host of The Show, KJZZ’s locally produced news magazine. Since starting at KJZZ in 2002, Brodie has been a host, reporter and producer, including several years covering the Arizona Legislature, based at the Capitol.