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  • NATURE PODCAST

The ‘zombie’ fires that keep burning under snow-covered forests

Listen to the latest science news, with Benjamin Thompson and Shamini Bundell.

In this episode:

00:56 The mysterious overwintering forest fires

Researchers have shown that fires can smoulder under snow in frozen northern forests before flaring up the following spring. Understanding how these so-called ‘zombie’ fires start and spread is vital in the fight against climate change.

Research Article: Scholten et al.

07:39 Research Highlights

Aesthetic bias means pretty plants receive the most research attention, and ancient tooth gunk reveals the evolution of the mouth microbiome.

Research Highlight: Flashy plants draw outsize share of scientists’ attention

Research Highlight: Microbes in Neanderthals’ mouths reveal their carb-laden diet

10:04 Briefing Chat

We discuss some highlights from the Nature Briefing. This time, Voyager 1 detects a faint interstellar ‘hum’, and a trove of Neanderthal bones found in an Italian cave.

Reuters: Faraway NASA probe detects the eerie hum of interstellar space

The Guardian: Remains of nine Neanderthals found in cave south of Rome

Video: Hawaii’s surprise volcanic eruption: Lessons from Kilauea 2018

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doi: https://doi.org/10.1038/d41586-021-01360-w

Transcript

Listen to the latest science news, with Benjamin Thompson and Shamini Bundell.

Host: Benjamin Thompson

Welcome back to the Nature Podcast. This week, mysterious zombie fires in frozen forests…

Host: Shamini Bundell

And the latest stories from the Nature Briefing. I’m Shamini Bundell.

Host: Benjamin Thompson

And I’m Benjamin Thompson.

[Jingle]

Host: Benjamin Thompson

First up on the show this week, reporter Geoff Marsh has been finding out about a very unusual type of forest fire that can seemingly rise from the dead.

Interviewer: Geoff Marsh

If you look down at the Earth from the North Pole, you’ll see a ring of conifer forest circling the Arctic wherever there’s land. This vast boreal forest crosses Alaska, Canada and Siberia, and it’s one of the last intact forests on the planet. But every summer, swathes of it are destroyed by fire, releasing large amounts of CO2 into the atmosphere, and as the climate warms, the fire seasons are getting worse. Understanding how these fires start and spread is vital in the fight against climate change, and this week in Nature a paper reports a spooky and somewhat alarming source of ignition known as a ‘zombie fire’. Here’s Sander Veraverbeke at Vrije Universiteit Amsterdam in the Netherlands.

Interviewee: Sander Veraverbeke

Fires in most of the world, these days, most of the fires are started by humans, but it’s different in the boreal. In the south of the boreal, okay, there’s still humans present there and human ignition remains important, but as soon as you go further to the north there is less human presence and then the natural ignition becomes the most important, and that is lightning. So, in the forests of Alaska and northwest Canada, about 90% of the burned area actually starts with a lightning strike. And then as we found in this paper, there is another kind of source of ignition as well which is a very intriguing one.

Interviewer: Geoff Marsh

Yeah, this is the so-called zombie fires. I couldn’t quite believe what I was reading. These are fires that stay alive, smouldering under the snow all winter and then pop up again.

Interviewee: Sander Veraverbeke

Yeah, so I was looking into these areas after some big fire seasons in 2014 and 2015, and we kind of linked those with extreme lightning occurrences. But then after that, I was also looking at the satellite images from the year after these big fire years and I was really intrigued because I saw like new fires kind of starting at the edge of the fire scar from the year before, and I was like this cannot be true almost, like is it really possible that a fire would just kind of sit and smoulder there under the snow? In the winter in these areas it gets down to -40 degrees Celsius. Would it be possible that it’s flaring up again?

Interviewer: Geoff Marsh

If fires really were overwintering, or indeed happening on a large scale, it could have implications for fire management and climate change. So, Sander set his then-new PhD student, Rebecca Scholten, to verify his hunch.

Interviewee: Rebecca Scholten

So, the very first thing he taught me was about these fires, and I was a bit doubtful to be honest. I didn’t really believe that this was actually happening, but, yeah, then I got into the research and we also talked to a lot of fire managers about it and they all said, ‘Yes, this is really happening,’ and yeah, that was really exciting I guess.

Interviewer: Geoff Marsh

So, people on the ground in this north boreal forest area already kind of had a knowledge of these zombie fires, did they?

Interviewee: Rebecca Scholten

Yes, exactly. Because we were lucky enough to get reports from fire managers and they told us of about 50 fires in Alaska and the Northwest Territories where they had seen this behaviour and this is how we started off, so this really was our reference data from the ground, and from then we looked at the satellite data.

Interviewer: Geoff Marsh

Just describe what that dataset looks like and what you can tell about what’s happening on the ground from up in a satellite.

Interviewee: Rebecca Scholten

Yeah, so, basically, what we are looking at are photographs. Of course, on these photographs we can’t really see if there’s a fire smouldering in the earth or in the soils but we know that when they’re smouldering under the snow, they don’t have a lot of oxygen so they cannot spread very fast, so we would always expect these fires very close to a fire scar of the previous year. We also know that these fires reflame, again, quite early in the fire season, so even before the usual fire season starts. We also use ground-based lightning data to check if there hasn’t been a lightning strike around the area, and we also use infrastructure and settlement data to check whether any humans were around because of course also humans can set the forest on fire quite early in the season.

Interviewer: Geoff Marsh

In your opinion then, are these overwintering fires just like very interesting but very rare anomalies, or are they common enough to cause a serious problem?

Interviewee: Rebecca Scholten

I think right now, based on our research in North America, we have to say they’re pretty rare and they only make up about 1% of the total burned areas, so they don’t contribute a lot. But we did find that there is relation to climate change, so these fires appear much more often after hot summers and large fire years, and we do see that more often.

Interviewer: Geoff Marsh

So, if we know these fires can overwinter and could potentially do so more often in the changing climate, then can we use what we know about them to predict future fires and maybe do something about it? I went back to Sander.

Interviewee: Sander Veraverbeke

There is definitely useful information in both where they have a high likelihood of occurring both in space and time, so that information of course tells us that we could monitor these locations with satellites but potentially also with planes. And you could potentially also like try to send someone there to extinguish that fire when it’s still really small so it never becomes a bit flaming forest fire again.

Interviewer: Geoff Marsh

And just give us a sense of the importance of this ecosystem for greenhouse gases. How much carbon is locked up above the ground and I suppose below the ground?

Interviewee: Sander Veraverbeke

In the top three metres of these soils in the boreal there is about twice as much carbon stored as currently in the atmosphere. The fires will of course not release all of that but they can release part of that and not only by the direct emissions by the fire but also after a fire you kind of remove that insulating, organic layer and because of that the permafrost deeper down may also start thawing, and if that happens that could release additional greenhouse gases into the atmosphere. So, if we can think about ways to better manage fires in these high northern regions, that would definitely be an important asset.

Host: Benjamin Thompson

That was Sander Veraverbeke and Rebecca Scholten from Vrije Universiteit Amsterdam in the Netherlands. You can find a link to their paper in the show notes.

Host: Shamini Bundell

Coming up in the show, we’ll be hearing about Voyager 1’s latest findings from outside the Solar System. That’s in the Briefing chat. But first, Dan Fox is here with this week’s Research Highlights.

[Jingle]

Dan Fox

Scientist, scientist, how does your research grow? Well, mostly with blue flowers and taller stems, according to a new analysis of the types of plants most likely to feature in scientific studies. A team of researchers looked at 280 studies published between 1975 and 2020 that focused on plant species typical of the southwestern Alps. They found that eye-catching plants, rather than rare or endangered ones, tended to attract scientists’ attention. Plants with blue flowers were the most studied, and plants with white, red or pink blossoms were investigated more often than those with brown or green flowers. Scientists also tended to examine plants with taller stems — probably because their flowering parts are more easily accessible than are those of plants with shorter stems. The authors suggest this ‘aesthetic bias’ could sway conservation efforts in favour of attractive plants, resulting in a lack of interest in less charming, yet often more endangered, species. Get to the root of that research in Nature Plants.

[Jingle]

Dan Fox

Your mouth is full of microscopic organisms, and so were the mouths of other members of the human family tree. Now, a team of researchers have harvested some of these microbes to better understand how our oral microbiome evolved. The team found the same ten types of bacterium in samples scraped from the teeth of modern humans, Neanderthals, monkeys and apes, pointing to the animals’ common origin. But Neanderthals and modern humans harboured bacteria that the others did not, including a group of Streptococcus bacteria which often help to digest starches. And genes that enable these Streptococcus bacteria to convert starches into energy-rich sugars were much more abundant in modern humans than in Neanderthals, hinting that reliance on starches grew during the course of human evolution. Chew over that research in the Proceedings of the National Academy of Sciences of the United States of America.

[Jingle]

Host: Shamini Bundell

It’s time now for the Briefing chat, where we discuss a couple of stories highlighted in the Nature Briefing. So, Ben, what have you got this week?

Host: Benjamin Thompson

Yeah, well, for my story this week, Shamini, I’ve got something that was reported in Reuters and it’s based on a Nature Astronomy paper, and it’s all about the latest findings from the Voyager 1 probe, which is currently over 14 billion miles – or 22 billion kilometres – away from the Earth as we speak right now.

Host: Shamini Bundell

And so, Voyager 1 is outside the Solar System. I’m trying to get a picture in my head of where is the edge of the Solar System.

Host: Benjamin Thompson

So, Voyager 1 was launched in 1977 and its job was to kind of study the outer planets – Jupiter, Saturn and what have you. And it just sort of kept going, and nine years ago, Shamini, it actually exited the Solar System in a place called the heliopause and it’s obviously kept going since then and travelled a bunch more miles. And it’s been collecting data as it’s gone and it’s discovered, well, a hum.

Host: Shamini Bundell

The thing is about leaving the Solar System is what’s it studying now? There shouldn’t really be much there? What is humming exactly?

Host: Benjamin Thompson

Well, that’s a great question and of course space is called space because there’s nothing there, right? Well, actually, in turns out that’s not the case at all, Shamini, as all the space scientists are screaming. And so, what it’s actually been collecting, it’s kind of the background noise in interstellar space and it’s coming from ripples or vibrations within this kind of ionised gas called plasma.

Host: Shamini Bundell

And when you say background noise, if I was there, could I hear it? Or is that a stupid question?

Host: Benjamin Thompson

I think that’s a legitimate question, Shamini. The answer is no, which is why I’m not playing it to you now – or am I – and what exactly is causing it is currently unknown, but it is this kind of constant noise and it seems like there is some sort of previously unknown activity in this gas, in this interstellar plasma, that exists between stars.

Host: Shamini Bundell

So, is space is actually, yeah, filled with plasma, how much do we know about it and what does the humming tell us?

Host: Benjamin Thompson

It’s pretty diffuse, Shamini. The researchers behind this work say there about 0.1 atoms for every cubic centimetre in plasma and you can compare that to the air we breathe on Earth that has billions of atoms for every cubic centimetre. So, not a lot there. Exactly what’s causing it though, again, isn’t entirely known just yet, but the fact it can be measured means that researchers can see the density of plasma that Voyager 1 is sort of swimming through as it goes along. And previously what’s happened is when it left the Solar System it was able to detect these kind of bursts of activity in the plasma, and that was kind of caused by the Sun being overactive and firing out a load of stuff, and the researchers say that was a bit like detecting a thunderstorm but what this is like is detecting some gentle rain in between, which is quite lovely. And, say, good on Voyager 1, off it goes, continuing its amazing journey.

Host: Shamini Bundell

Well, I just love the idea that these sort of scientists of Voyager 1 are just sort of listening to space humming. That’s lovely, much nicer than my story this week, which is a little bit more on the gruesome side. So, I have been reading an article in The Guardian about a treasure trove of Neanderthal bones in a cave in Italy.

Host: Benjamin Thompson

Well, a couple of podcasts ago, Shamini, we had that story about evidence of deliberate kind of ceremonial human burial. Is this kind of similar to that? Do we know what happened to these Neanderthals?

Host: Shamini Bundell

Well, that’s, I guess, the big mystery, and actually this particular cave is interesting because this isn’t the first time that Neanderthal bones have been found there. So, I think the first time was in 1939 and they discovered a Neanderthal skull there and based on the damage to the skull – it had a hole in it – there was a theory at that time that, ‘Hey, this could tell us about Neanderthal burial practices or how Neanderthals treated their dead,’ and there was a theory that it was evidence of ritualistic cannibalism. Now, that hasn’t remained a terribly popular theory in the decade since, and that cave complex hasn’t been investigated now since the 50s, but in the last couple of years they’ve been looking again and they’ve been looking in particular at an area that sort of really wasn’t previously accessible and which they think a cave-in has managed to protect and preserve the bones that are there.

Host: Benjamin Thompson

So, a fortuitous event that led to these bones being uncovered then, and you’ve said bones plural there, so I imagine there’s a few that have been found.

Host: Shamini Bundell

Yeah, loads. So, I mean, I think this is the thing that has sort of most excited researchers in the field. They have found remains belonging to seven adult males, one female and a younger boy, and this isn’t all one group of Neanderthals hanging out together. They’re from different time frames, some of them as old as maybe 100,000 years old, some more recent, and the key evidence that has been obvious straight off from these bones is that a lot of them have been gnawed on by hyenas. And it’s not just Neanderthal bones – there are other animal bones there as well – and they think that maybe this cave could at some point have been a sort of hyena larder.

Host: Benjamin Thompson

Right, well, quite macabre, Shamini, my goodness. Is it the hyenas that did for these Neanderthals do we think?

Host: Shamini Bundell

It’s not 100% clear whether the hyenas maybe hunted them or whether the hyenas scavenged a dead body and then sort of dragged it back, and it’s also not necessarily the case that all the bones are from hyena kills. It could be that at some time Neanderthals themselves lived there, but what we do know is that this cave – which is now a really significant site having given up so many bones – was in a place where the Neanderthals were really doing well and thriving and lived for tens of thousands of years.

Host: Benjamin Thompson

And so, what’s next then, Shamini?

Host: Shamini Bundell

Well, I think this is just the beginning. Having all these bones is brilliant for the archaeologists and there’s a lot that bones can tell you. So, we heard from Dan earlier about a study looking at what genomes from the teeth can tell us about Neanderthals diets and similarly here they’ve sort of done a very preliminary analysis of the sort of tartar to show what they were eating. But the plan is to sort of dig a lot deeper, looking for DNA, for evidence of illnesses, pathologies, what their bones tell us about their activity levels, and they’re still looking in this cave. I think they’re hoping to find maybe evidence of tools, things that could tell us more about Neanderthal culture. But everyone is basically excited to have this sort of extraordinary find of so much material and a site that is so well preserved and could yet yield more secrets.

Host: Benjamin Thompson

Well, extraordinary is right, Shamini. What a find and thank you for bringing it to the Briefing chat this week. Listeners, if you’d like to know more about these stories and more like them but have that information delivered directly to your inbox then you should sign up for the Nature Briefing, and check out the show notes where you can find a link to do so.

Host: Shamini Bundell

Before we go, we’ve got a new video for you out on our YouTube channel. It’s about an unexpected eruption on Hawaii three years ago, and the volcanologists who’ve been trying to piece together what happened. There’ll be a link to that in the show notes. But for now, that is all for the Nature Podcast. Don’t forget, as always you can follow us on Twitter – we’re @NaturePodcast.

Host: Benjamin Thompson

And you can reach out to us on email – we’re podcast@nature.com. I’m Benjamin Thompson.

Host: Shamini Bundell

And I’m Shamini Bundell. Thanks for listening.

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