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Surviving the Pyrocene



For those of us living in the United States, forest fires have dominated headlines, as billowing smoke from Canadian wildfires has cloaked, and choked, much of the Eastern Seaboard in recent months. For more on what is happening to our planet, The Explorers Journal reached out to two luminaries in the study of nature’s pyrotechnics—storm chaser George Kourounis and U.S. Forest Service ecologist Gavin Jones, whose landmark study on wildlife adaptation in the age of the Pyrocene was published in early July.

GEORGE KOUROUNIS: Until I read your latest paper in Trends in Ecology & Evolution, I had not yet encountered the term “Pyrocene,” which is a bit surprising given how often I have ventured into forest fires during my career. Define the idea of the Pyrocene, its significance, and, if you will, how it differs from other geological periods.

GAVIN JONES: Actually, it was Stephen Pyne, the famous fire historian, who actually coined the term Pyrocene—our current epoch of time in which we’re seeing far greater fire activity than we have in the past. The key driver of it is human activity, which is causing larger, more severe, more frequent catastrophic fire events, and, in particular, more frequent intersections of those fires with human communities.

GK: What is frightening is that now, in the summer of 2023, we’re only part way through the year. In Canada, where I am based, we’ve already burned more than four times the national average, and there’s still plenty of fire season left. The fires are ramping up. They haven’t plateaued.

GJ: And, just like with climate change, people are simply calling it the new normal. Well, it’s not normal because it’s not stable. We are experiencing a dynamic, chaotic change.

GK: Your specialty is in the “dance,” if you will, between fire and evolution, and specifically how one affects the other. What are some specific ways in which fire can drive evolutionary processes and over what time frame?

GJ: My specialty is the effects of wildfire on wildlife. And, until recently, I hadn’t thought about evolution as a factor that is very much in play. As a conservation biologist and wildlife ecologist, I’ve spent most of my career monitoring populations of animals before and after wildfires. Did they go up? 

Did they go down? What were the direct, proximate effects of a wildfire on a species and what does that mean for conservation?

But in the past couple of years, I started to think about evolution as a factor, when I began noting adaptations to fire events in various species. How is fire driving that evolution? And what are those mechanisms? Evolution tends to be defined by minor and graded changes in the genetic makeup of a population with each generation. But there is also the sexy side of evolution—natural selection—which Charles Darwin so cogently studied and wrote about. If there is environmental pressure on a species, there will be differential survival rates among members of that species, depending on individual capacities to withstand that pressure. You’re going to have a changed template for that surviving population, and its potential edge when it comes to withstanding the next disturbance even better. Environmental pressures often come as a result of natural disasters, change agents that can cause significant mortality in a shortened time frame.

Fire is probably one of the most, if not the most, influential agent of change on Earth. Every ecosystem that has vegetation has a source of ignition, and thus has a fire regime—a consistent, predictable, pervasive force over millions of years, which has no doubt had an impact evolutionary change.

We often think of evolution as happening over long periods of time, but it can happen in a single generation, and it can even happen in a significant way for longlived vertebrates over the course of several generations. It was some recent work by French evolutionary biologist Timothée Bonnet that really got us thinking about this, as he has shown that there’s far more capacity for rapid evolutionary change in wild animals than we thought. If you consider fire as a key driver, we began looking at what that means for animal evolution in ecological time.

GK: Instead of talking about geologic time, you’re calling it ecological time. And you are starting to see small changes in just a few generations or less, because fire has such a dramatic effect on the entire ecosystem. In your paper, you talk at depth about species that are fire adapted—whether they are “fire naive” or “fire savvy.” Can you give me a few specific examples?

GJ: One of the examples that we talk about in the paper is the frilled-neck lizard in Australia (Chlamydosaurus kingii). These guys have come to be well adapted to wildfires, surviving under normal historical conditions in terms of fire regime. During the early part of the fire season, in November and December, we’ll typically have fires that burn along the understory of the forest while leaving the overstory intact. The lizards just climb up in the tree canopies and wait it out, having sensed the fire coming in. Historically, they have survived quite well. The concern now is that they’re going to be quite poorly adapted to changing fire regimes. There is this invasive grass that has taken hold in their habitat, which is taller, and it burns hotter, so these typical early season fires that would come in and normally not touch the canopies are now burning into the canopies as they are becoming more flammable. The consequence is that this species, which has this great adapted response to fire, is now responding inappropriately to this new kind of fire regime, and so that’s an example of what we call a maladaptation or an evolutionary trap. Their response has been correct based on evolutionary history, but is ill-suited to the new conditions.

A neat example of one animal that has capitalized on fire is the black kite, also in Australia. The black kite is a raptor, a predatory bird species that has been observed picking up burning sticks from fires, carrying them into unburned places, and dropping them in order to force prey out into the open where they can catch them. It’s nuts! They’re actually engineering the landscape and the fire regime itself through the intentional spreading of fire.

GK: Is that a learned behavior? Or is that something that is an evolutionary response? And it totally sounds like tool use. Doing their own prescribed burns! That blows my mind. 

GJ: It’s pretty wild that, in that environment, there’s been a selection for individuals that are willing to take those risks for the high payoff, right? If you think about it, it’s really cultural evolution. They’re transmitting behaviors through learning. It’s incredible.

GK: And what animal adaptations to fire do you observe here in North America?

GJ: I am glad you asked, as I have done quite a bit of work on spotted owls in California and the Pacific Northwest. While we didn’t use this example in the paper, I’m a little biased as I’ve spent 10 or 12 years studying this species from the perspective of: “What’s their ecological response to wildfire?” It has been very much from a conservation management type of perspective. How can we manage forests, and this wildfire landscape, in a way that benefits the owl, et cetera? But a few years back, we did a study that was a bit of a spur off of my dissertation where we attached GPS tags to some 25 spotted owls. And for a few years we got thousands of data points on their locations and documented their nocturnal foraging activity. Some of the questions that came up were: 

How do they interact with characteristics of a burned landscape? Do they use places that have burned severely? Do they use places that have burned moderately or lightly? What are their preferences?

What we found is that there’s a certain patch size of a severely burned forest that is kind of optimal for the owl. We found that smaller patches of severely burned forest provide these little gaps that allow the owls to hang out along the forest edge, while hunting into the open, where there’ll be little wood rats and mice and voles scurrying around. The burn area gave them a greater access to that food resource, while the forest edge concealed them from their prey as well as their predators, as the owls get attacked and eaten by hawks and great horned owls.

We found that they like these small patches of severely burned forest up to a certain point—about 10 hectares being the maximum size they’ll use. It turns out that 10 hectares is also just about the maximum, historical patch size for high-severity fire in the region over the past 10,000 years or so, based on reconstruction of fire history carried out by dendrochronologists and paleoecologists. The numbers just matched up perfectly, indicating, potentially, that owls are showing this evolutionary response or an adaptive response. In larger burn areas, which we are seeing more of now, the owls are nowhere to be seen.

GK: So, they have yet to adapt to these new fire regimes—these much bigger, hotter fires that are becoming more common and burning huge tracts of land?

GJ: We know from some other studies that we’ve done that when we have those big, hot fires, owls go locally extinct. They don’t hang out in those places that are burned severely, and the ones that do survive don’t use those landscapes. So basically, it’s just like a habitat loss situation for them. That’s one of the cooler examples in western North America that I’m very familiar with because I’ve been working on it for quite a while.

GK: I’m curious to get your opinion on the role of understanding the relationship between wildlife and fire in the context of conservation, moving forward

GJ: Our entire conservation paradigm in Western culture, in North America in particular, is what I and others refer to as “fortress conservation.” So, what does that mean? It means we find a place that we think is important, and we draw a box around it to protect it. And certainly, that’s needed in some situations, right? When wilderness areas are facing a major threat—urban development, clearcutting, and such. You protect areas for spotted owls, for example, and this is the case in the Sierra Nevada, where I spend a lot of my time working, or in the Lincoln National Forest. And, for the past century or so, fortress conservation has worked really well [laughs]; it’s very effective at stopping forces from getting into those places, including wildfire.

But now we can no longer stop wildfires from getting into those places, and so this idea that we can draw a box around something and hold the line is outdated.

It no longer works with the kinds of threats that we’re seeing to our landscapes that involve larger forces, like fire, like drought, like climate change, et cetera. And so, I think the idea that we need to embrace fire as a natural process in the ecosystem is certainly becoming much more of a prominent idea in conservation as we realize it’s an inevitable thing.

So how do you want it? Do you want it in a way where you can have some control over it? Or do you want it in a way where you have no control over it at all?

And it’s the same thing with people complaining about smoke. You’re going to get smoke, as so many of us are experiencing this summer. How would you like your smoke? Would you like your smoke in a predictable way, where you get a little bit here and there every summer? Or every10 years you get an absolute apocalyptic smoke bomb. It’s the same thing with fire.

I think that today there’s very much a heightened appreciation of the role of fire in conservation. 

Some of the other work that I’ve been involved in over the past couple of years revolves around what’s called the “pyrodiversity-biodiversity” hypothesis. This idea that, within any given landscape, the more variety of fire characteristics that you have, the greater number of species you’re going to have there. The greater variation of a landscape that’s driven by fire as a major agent of change, the more niche space you’re going to have for different kinds of species to coexist.

GK: It’s the great irony, right? You protect an area from fire for so long that it hasn’t had the chance to naturally burn out and then you get the really big fires.

GJ: By trying to protect something, you destroy the thing you’re trying to protect.

GK: The road to Hell is paved with good intentions.

GJ: It’s a good intention, yet it’s a very Western idea that man and nature are separate. The idea that we can draw boxes around nature and stay out of it is a very white Western idea, actually.

Look at a lot of Indigenous cultures— they use fire all the time to benefit their resources. Ultimately, that kind of use of fire by cultures produces resilient landscapes and diverse biota. GK: Looking to the future, what do you think we’ll see in the next decade or two, both from a fire perspective and from an evolutionary perspective?

GJ: I expect we will see a lot more. It’s getting warmer, and in a lot of our landscapes we have sort of a fire deficit. They’re due, it’s time to burn and they’re going to burn, big and hot. It’s going to get worse before it gets better, if it gets better at all. Fire is not going to leave the public consciousness anytime soon, so we have to learn to live with it.

And from an evolutionary perspective, I would expect that this is the time when we’re going to see some of the most rapid changes in evolutionary trajectories of animals in response to fire. 

If you were to write your history book 1,000 years from now, you would probably look at these next 10 years and say, that was a really critical point in the evolutionary trajectory of wildlife or animals on Earth in response to this regime, this fire regime, this global phenomenon.

We can use our crystal ball and forecast the conditions, but evolution is not a very predictable thing. It just follows its nose, wherever it goes. But I expect to see in animals some rapid evolution in the areas of sensory ecology—their ability to sense, to detect, and to respond to cues related to fire. Can they develop an earlier detection system than might enable them to escape? We’ve been seeing that evolution in response to fire can happen rapidly, but can it happen rapidly enough? That is the question.

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