NAU is researching how this unique, tiny cactus responds to fire

Research taking place in northern Arizona could offer clues about how some cactuses respond to fire.

Clare Aslan is an Northern Arizona University professor and a conservation biologist; she’s been monitoring the paradine plains cactus in areas burned by the Dragon Bravo and White Sage fires last year.

She says she gets that it may seem like scientists are paying a lot of attention to an admittedly very small cactus. But Aslan says trying to understand how, when and where systems recover from fire is important for managing the landscape. That’s especially true, she says, as fires become bigger and more intense.

Aslan joined The Show to talk more about this.

Full conversation

MARK BRODIE: And, Clare, could you please describe what this cactus looks like for those of us maybe who have seen it but aren't quite sure?

CLARE ASLAN: Sure, sure. So this cactus, the paradine plains cactus, is extremely small. It actually can fit in the palm of your hand quite easily. It's also very low to the ground. So when you are standing above it looking down, it often looks like it's barely poking up above the surface. It's almost flush with the ground itself.

It's kind of a little bit of an olive green color with some fairly soft spines. It won't it won't poke you like a prickly pear might do. And it contains these these flowers in April and May, which are very beautiful. They range from kind of white to a peach color that are almost as big as the entire surface of the plant. So oftentimes the flower is what you see first.

Austin Aslan

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Handout

MARK BRODIE: OK, and am I right that this particular type of cactus has some kind of unusual seasonal behavior irrespective of how it interacts with fire?

CLARE ASLAN: Yes. So this particular cactus and its close relatives have what's called contractile roots. And this means that when the cactus feels stressed, and this may be because it's very dry or possibly because it's very cold, those roots can actually contract and pull the entire plant down kind of into the ground. And they live in a very an area with very sort of loose sediment, and so that sediment can sort of sift over top of the plant, which means that the plant can actually go underground.

So, and then when things improve, when it gets warmer or when it gets a little bit wet, those roots sort of reinflate and push that plant back up, and they pop back up. And so you can go to a site and not be able to find them and go a month later and there they are.

MARK BRODIE: So does that make it any less surprising to you that these cacti maybe act a little bit differently when they come into contact with fire than other species?

CLARE ASLAN: I think it does indicate that these cacti are very responsive to their environment and to relatively short-term changes in the environment, and also that a lot of what is going on with regard to these cacti is happening underground.

And I should say that we know from old herbarium specimens where people actually dug up whole plants, so this may have been 50 years ago, that a lot of the plant is below ground. So as I describe it to you as this super tiny plant that you can barely see, that's not the entire story. There's more of this cactus going on down there.

So when it comes to fire, I do think that that might be part of the reason that we've seen some resilience in these individual plants is that they may have that kind of built-in protection that perhaps is intended for temperature or for moisture, but it may come in handy when it comes to a fire event as well.

MARK BRODIE: Interesting. OK, so tell me what exactly it is that you're going to be looking at and looking for during this project up in the area where there were some pretty significant fires over the last year or so.

CLARE ASLAN: Yeah. So this cactus is known as a species of concern. It's actually not a listed endangered species, but a number of very close relatives are. And because it's a species of concern, and actually to try to prevent it from becoming endangered, there's been long-term monitoring that's been going on. We've been tracking these cacti kind of year to year, checking out their flowering, looking at their pollinators, getting a sense of where the central populations are.

So then the fire comes along, and some of the most high-severity areas, particularly of the White Sage Fire, but also some portions of the Dragon Bravo Fire, overlapped directly with where these cacti occur.

So I went out there a few weeks after the fire was finally declared fully over last October, and remarkably found that almost the only green thing you could see in some of these sites were these super tiny cacti. So that really led us to realize, wow, these these plants, at least some of them, have survived in the immediate aftermath of the fire. We have all this monitoring data. Let's try to see if we can use that data to compare how the plants are doing now with how they were doing in the past and get a sense of how well they're going to do going forward.

So over these next couple of years, our goal is to monitor individual plants to determine if their survival lasts — basically, can they make it a whole year after the fire, particularly in cases where the plant was visibly damaged? And then do they still reproduce? Are they able to carry out their functions as this community starts to recover from this event?

MARK BRODIE: Oh, that's interesting. So is there a chance maybe that the individual plant survives but like it won't be able to reproduce? That it might be the last one of that particular kind?

CLARE ASLAN: Right, that's kind of the the question. Mainly because some of these plants do show some damage. So there's a little spot of green, which is remarkable, but when you get close, there's kind of burned cactus spines surrounding sort of in the in the soil surrounding that. So we know that there was some damage.

Also, again, because they are mostly underground and we don't want to risk disturbing them further, we don't really know whether any form of soil heating might have affected the broader cactus structure underground. So this year, we were able to observe flowers, which was really wonderful. They they did flower, but I haven't observed very many fruits, and a cactus has to invest a lot of moisture to create a fruit.

And that leads us to wonder if perhaps these plants are still so stressed out, they may be still recovering from this damage or still feeling that damage, so they haven't yet been able to make that investment in fruits.

MARK BRODIE: Do you have a sense of why it is that some of the cacti maybe had some damage and some didn't? Like is it just a matter of where the fire happened to burn, or is there maybe reason to think that some of the cacti were in the fire but didn't actually get damaged?

CLARE ASLAN: Yeah, it's a great question. I do think I'm seeing that. There's one particular area where we have an unusually high density of the plants, and that area does happen to coincide with some of the higher severity portions of the of the fire. So the trees that are above these cacti, so kind of the canopy, a lot of those trees were killed by the fire. And in that same area, I do see some individual cacti that are clearly damaged. As I mentioned, there's some burn spines, but there's still some green portions. There's a few that are totally dead and clearly burned, but then there's quite a few that look great. They kind of look like nothing happened.

And so the question I kind of have in my head, and I may never know the answer, is, is that because those particular ones happened to be underground at the moment that the fire burned, or was there some other reason that they escaped? But we do really see the entire range of conditions.

MARK BRODIE: Do you think it's possible — and maybe it's not possible to know this yet — but do you think that it will be possible to take what you learn from this particular species of cactus and extrapolate it out to look at how other species of cactus or other even other species of plants respond to fire?

CLARE ASLAN: We do know that these systems in this region are fire-adapted. So all the plants, all the plant species, will have experienced fire to some degree, and plants respond to fire in different ways.

Some of them may not survive the fire themselves, but they are able to reproduce, and their offspring will emerge quickly after fire. Others can actually survive the fire itself. It's a wide range.

I think the thing that makes this particular plant so unique is this funny behavior it has of kind of disappearing and reappearing, its rarity across the landscape, and its extremely tiny size. It's such a remarkable sort of distinction that this plant has compared to others that in terms of being the only green thing that we saw after the fire, it does make me wonder if it's giving us some insight into some new forms of adaptation to a fire that we hadn't necessarily described before.

MARK BRODIE: All right. Clare, thanks so much for the conversation. I really appreciate it.

CLARE ASLAN: Yeah, thanks so much for being interested.

MARK BRODIE: Clare Aslan is a professor at Northern Arizona University and a conservation biologist.

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