Getting blasted by a bolt from the heavens usually spells the end for trees, but some species not only survive these strikes, they thrive.
Host Belinda Smith talks with guest Cary forest ecologist Evan Gora about his research on tropical tree mortality and how the Tonka Bean tree has adapted to survive lightning strikes.
Transcript
Belinda Smith: Few phenomena are as awe inspiring as lightning.
There's a good reason we're told not to stand under a tree during a thunderstorm. If it gets struck by lightning, the liquid inside can vaporise and the tree can explode. Or a lightning bolt might hit, but leave no discernible signs of damage, but destroy the roots below. And maybe months down the track, the tree dies.
But there are species that don't just seem to survive lightning strikes. They thrive like a statuesque panamanian rainforest tree, which more often than not, flourishes with each bolt from the heavens. That's according to a study out earlier this year, and I spoke to the lead author.
Evan Gora: My name is Evan Gora.
I am a forest ecologist working at the Cary Institute of Ecosystem Studies and also the Smithsonian Tropical Research Institute.
Belinda Smith: You did this research in a rainforest in Central Panama. Is this a lightning hotspot?
Evan Gora: Central Panama receives a lot of lightning strikes, depending how you measure it. You can sort of get different numbers, but it's definitely above like the 75th percentile, um, in terms of tropical forests around the world and, and.
The amount of lightning strikes it sees and tropical force already on their own receive a lot of lightning. So that's, that's saying something. Um, in that forest, on average, there are about 12 lightning strikes that hit the ground per kilometer squared per year. Um, and in a lot of places around the world, that number's closer to like 0.5.
So it's a big number. There are a lot.
Belinda Smith: Now this area gets so much lightning because it's near the equator. So when the sun comes up, it shines directly onto the forest. Heating up the air, that warm air quickly rises into the atmosphere mixing with the cool air above.
Evan Gora: When you get this start of this vertical mixing cycle, and fundamentally at its most basic, lightning is a static shock that's produced by air mixing vertically, and it's really the same process you might have when you reach for it.
Doorknob and get zapped. Instead of that shock traveling two millimeters from the doorknob, it's traveling, you know, 10, 15 kilometers from the atmosphere to the earth's surface. And with that greater distance comes much, much greater power
Belinda Smith: despite all this lightning flashing around. I. There was pretty much no research done on how it affected the rainforest below until the seed of an idea was planted in the mind of one of Evan's colleagues back in the nineties.
Evan Gora: He was a PhD student at the time, studying invertebrates in this particular rainforest
While he was walking through the forest, lightning almost hit him. He landed like right next to him, and when he didn't die, he then walked over and looked at the trees that had been hit and they looked fine. Yeah. It was like nothing happened.
Belinda Smith: This coupled with lightning's unpredictability were two reasons it went unstudied for so long I. Luckily for Evan, who a bit over a decade ago started this lightning project, technology has made it possible to track lightning strikes as they happen.
Evan Gora: So we started using a system of cameras. Um, we've now advanced to a more advanced system of electric field change meters.
Basically fancy antennas that record the electric potential in the atmosphere. And so basically the voltage of the atmosphere and how it's changing, um, about 10 million times every second, is basically measuring radio waves as they wash across the atmosphere. And with those different systems, we can pinpoint where lightning must have occurred and then walk out in the forest and record what's happening
Belinda Smith: in the beginning.
This was easier said than done. Evan remembers the very first lightning strike they detected on the cameras
Evan Gora: when we got there. You know, we're still actually, you know, looking for. Blown up trees or trees that have dropped all their leaves or maybe some evidence of fire. And I'm walking around the forest for days at this point not finding it.
And I a tree climb as well. So I started climbing trees to get a bread to look in the canopies. I saw one tree that had a lot of defoliation, so it was starting to defoliate, so I just started to climb its neighbor. About halfway up the neighbor, I started to realize that the neighbor was losing some leaves also, and it had some beetles attacking its trunk.
And then I started to notice those flashover locations. So basically every single tree that was close to this one ends of the nearby branches were defoliating. It's actually, it's, it's necro as they turn black. If you don't know, it almost looks like they're burned. But it's actually just what happens when like a green leafy tissue rapidly dies.
Belinda Smith: It's a telltale sign of electric current jumping from tree to tree. And Evan started seeing these black leaves all around the tree he'd climbed
Evan Gora: and realise, oh, this, this tree I'm climbing has actually been struck by lightning and is damaged. And, you know, since that event, um, we've started applying that approach and we can identify those damaged locations really consistently.
Um, so that sort of set us up for. Years. We would pull these video cards from the cameras, um, run them through the algorithm track where the lightning must struck, walk out in the forest, and then confirm which trees were damaged based on this diagnostic. This this pattern of electric current jumping among trees
Belinda Smith: by tracking lightning strikes and the fates of the trees in the areas that was struck.
Over the next decade, Evan and his colleagues learned two main things. One, lightning is a major killer of the forest's, large trees.
Evan Gora: I mean, this is important because large trees are important. So the largest 1% of trees in forests, which we often call giant trees, contain about half of all the biomass, the largest tree, for example, in this forest we work in Panama, is about a thousand times larger than the medium tree, which means that this phenomena lightning that we've largely ignored in tropical forest ecology for, uh, more than a century, turns out to actually be one of the most important drivers of tree death and therefore.
Forest function in, in a way that was really, really surprising. The second big finding, a very interesting follow up to that is, you know, where we're seeing in the forest, lightning is killing a lot of these large trees, but not all of 'em. Um, we see that sometimes trees survive and not only do sometimes trees survive, but sometimes, you know, we have these directly strucked trees that are in remarkably great condition while the trees around them are dying.
And as those observations started to build up over the, the 10 year duration of this project, we noticed that some species are consistently those individuals in the center of a lightning strike that are surviving and one in particular dip. Dirks ola Ara, um, is a species we've spent a lot of time studying because it appears not just to survive lightning strikes, but actually benefit from being struck by lightning.
Belinda Smith: Yeah, you heard right. This tree in dip tricks, Ali benefits from being struck by lightning.
Evan Gora: These are trees with an orangeish, flaky bark, very large leaves. Typically these trees are 30 to 50, 55 meters in height. They have massive trunks and they also have massive buttresses at their base. So basically these like wide legs almost that, that hold them up
Belinda Smith: and they're bigger than most other trees in the rainforest.
Evan Gora: They're um, about 50% taller than average for a tree of the same diameter, and their crown areas are about 30% larger. So this suggests that these trees, even for a given diameter, are massively more likely to be struck by lightning than other species. This seems to be possible 'cause when these trees are struck by lightning, they exhibit almost no damage at all.
Evan Gora: Remarkably, remarkably healthy. And not only do these trees survive when they're struck by lightning, but those same lightning strikes tend to kill a lot of their neighbours. Um, for the lightning strikes we looked at, on average, nine of their neighbours were killed. Um, it was about two metric tons of neighbour biomass were killed in these events.
Belinda Smith: The team calculated that trees living next to Diptera Lyra had a 40% higher risk of mortality. That's how efficient lightning is at killing off Diptera neighbours,
Evan Gora: and not only are the neighbouring competitor trees killed, but also the lianas that colonise their canopies. So Lianas are woody vines.
They're actually very bad for trees. They colonize their crowns. They compete for light resources, water dip tricks. It's a very shade intolerant tree. So basically it does not handle something competing for light with it very well,
Belinda Smith: but with a handy lightning strike or two, those lianas shrivel die and fall off leaving the tree to soak up all that sunshine.
Evan Gora: Like in all these ways, we see the population benefits and then we basically took all of these data and put them into computer models to quantify how much this should matter. Um, and what we essentially find is that. Um, these species are able to reproduce about 14 fold more. Um, basically more than 90% of their reproduction is attributable to this ability to survive lightning, um, which is really remarkable.
Belinda Smith: You are listening to the side show on ABC radio national with me, Belinda Smith. So how are these trees able to withstand direct hits by lightning while surrounding species seem to just car it?
Evan Gora: Our leading hypothesis for why Diptera is able to survive lightning when many other species do not.
Actually comes down to their electrical properties. So basically, if a tree or if anything is more conductive when a certain amount of electric current passes through it, it'll generate less heat energy. You would know this at home, if you ever have any old, really old chargers or old lamps. If the wires get really hot, that's causing more resistance to electric current and basically creating heat energy.
We've gone out in the forest and measured tree electrical resistance, which so far we've only been able to do for a very small number of species. We found that Dip Rix was a particularly conductive tree species. So we see that it's very, very electrically conductive. If you put those data into a mathematical model, which we've done, um, you'd estimate that it's gonna then produce much less heat than other species, which might mean then it's gonna experience less damage.
And, and we think there's, there's likely some validity to this and it's something we're, we're pursuing now.
Belinda Smith: It's wild to think that a tree could evolve to thrive with each lightning strike, but it's even more unbelievable to think that this is the only example of this. Are there other species which seem to do well with lightning?
Evan Gora: We think this actually might be a common characteristic among tree species that really rely on a stage of their life history, where they're really large individuals that repro a lot. And we identified several species in Panama that we think exhibit the same trend, and we didn't have enough instances of them being struck by lightning.
You know, maybe one or two individuals to really quantitatively demonstrate that this is true. But we looked also at these trees, a lot of different data, and we have pretty much a smoking gun that there are several species that also survive. And then when you talk to people around the world and you look at the literature.
Some of these are anecdotes. Um, some of them have more data suggesting that there are a lot of species that might survive lightning. So this might be just this characteristic we never really knew was important, could play a major role in, in shaping forest dynamics around the world.
Belinda Smith: Even in forests, in faraway places like Australia.
Here we mostly associate lightning strikes in forests with bush fires. What happens when trees are hit and don't catch a light? To find out, I went off to Brimbank Park in Melbourne's West.
Gary Moore: I'm Greg
Belinda Smith: Moore. Oh, okay. Hey Greg.
Gary Moore: Good. Hi. I thought you liked Belinda. Thanks. Thanks.
Gary Moore: there's not that much written on lightning struck trees, so you, you don't have to be a super duper expert to, to take an interest in it.
Um, but I have been interested in lightning s struck trees for a long time, and when I get the opportunity, I go, uh, and visit them. When former students and colleagues tell me that there's been a lightning struck tree,
Belinda Smith: this is Greg Moore. He's a senior research associate at the University of Melbourne who specializes in urban trees in Australia.
Gary Moore: We, we know that some trees are growing in locations where they're more likely to be lightning struck. Uh, and we know that quite a number of those do survive. So for example, we do know that, uh, Mountain Ash. Eucalyptus Renan. Mm-hmm. Magnificent. Australian species. Hybrid. Yeah. One of the, one of the great eucalypts is quite prone to lightning strike because it's so tall.
A number of the specimens that have been struck, uh, have not only survived, but have continued to grow well. So you have a bush fire, a few of them out Nash survive. They're usually called stags or um, survivors after the
Belinda Smith: fires. The reason they're called stags is because they can lose the odd big branch here and there, and over the decades what's left can resemble antlers,
Gary Moore: and if all the other vegetation around them has gone, you've got a 70 metre tall Mountain Ash with nothing around it.
Lightning storm comes through. What are the odds? Oh, yeah. Very high. Mm-hmm. And so you often see a mountain ash that's been struck, not once, not twice, not three times, not four times, but maybe, you know, up to eight times, um, because it's been so much taller than everything else around it. And it'll do well, not just in the, uh, short term and for a mountain as short term as, you know, 30 or 40 years.
Uh, but for a hundred years later they're still going strong and un until they get struck again, or another storm gets some, they'll continue to do very well.
Belinda Smith: So the Panamanian study looked at dip tricks, lira, which grows in rainforests.
Gary Moore: So Mountain Ash don't go in a rainforest, but they do go in something that's quite close to what we would call a, a wet forest or a wet sclera fill forest in the past.
Uh, but if you think about the tropical rainforest or the subtropical rainforests up around, uh, Brisbane or Northern New South Wales, they have what are called emergence. Now emergence are the, the trees, the, the, the tallest growing trees in the rainforest. And you know that the rainforest canopy is normally pretty even, but every so often one comes up above.
The rest of the canopy, and that's the emergent
Belinda Smith: being so much taller than the rest of the canopy. That emergent tree is just asking to be struck by lightning and when it is.
Gary Moore: One of the things that can happen is that the tree dies and collapses, and it opens up the canopy. Now, as soon as you open up the canopy, you have the potential for renewal.
A tree dying here, uh, opens up. Renewal another bit there, another bit there. And over time, you, you may have a whole group of different little parts. Of communities making up this general mosaic, which gives the, the, the, the splendid diversity, not just in the habitats, uh, and micro habitats of the rainforest, but in the species.
And so in that case, you could well argue that rainforest, that, that the, the lightning strike and the storms that before these, uh, emergence in rainforest, a really good and constructive thing.
Belinda Smith: As for forest ecologist, Evan Gora, he and his team are taking their work and expanding it in a big way.
Evan Gora: Pretty much all of the really comprehensive data we have on lightning strikes, we're attracting them and going ing.
What's happening is in one old growth forest in Panama, and, and that's not enough. So we wanna understand, you know, how do the effects of lightning vary when you have forests to different ages or different compositions or maybe in mangroves versus, you know, a, a, a lowland dryer forest. So we are conducting a project now also in Panama, using these new sensors where we track lightning strikes across the entire centre part of the country.
Expanding from 15 square kilometres to 8,000.
Belinda Smith: That was Evan Gora Forest ecologist at the Cary Institute of Ecosystem Studies and the Smithsonian Tropical Research Institute. He and his colleagues published their study into lightning struck trees in the journal, new cytology in March.
