This week, President Donald Trump graced California with his bilious presence so that he could flump around the state saying stupid things about the wildfires that have been tearing along the west coast destroying homes and making the air unbreathable. It’s always hard to pick out just one idiotic thing that Trump says, since every time he opens his mouth the entire universe gets a little stupider, but a lot of attention has been paid to this particular quote, said in response to a question about how he’d like to see forests better managed. I include it here unedited from the official White House transcript:
“But with regard to the forest: When trees fall down, after a short period of time — about 18 months — they become very dry. They become, really, like a matchstick. And they get up — you know, there’s no more water pouring through, and they become very, very — well, they just explode. They can explode.”
I heard of this via my Twitch followers, who pointed out that no, trees do not explode. And when I looked up the full quote later one of the top results was from wildfiretoday.com which announced “Once and for all — trees do not explode.”
And I found all this very interesting because in fact yeah, trees kind of do explode.
Holy shit, am I making a video about how Donald Trump is right about something? And at least one obvious expert at wildfiretoday.com is wrong? I...I kind of am? Sort of? Look, 2020 is a weird time. But let me say this up front: “explode” is a problematic word here. It means different things to different people, and when I talk about how trees can explode, I may not mean what you first think of when you hear the word “explode.”
When I first moved to Northern California and noticed that everything was on fire, I heard about the nightmare that is the eucalyptus. I previously only knew the eucalyptus as a tree that produces smelly oil and koalas (note that I’ve since learned koalas do NOT grow on eucalyptus trees), but it turns out there’s more to them than that. The first thing I heard here was “eucalyptus trees are an invasive species that doesn’t belong in California” and the second thing I heard was “also they explode.”
Now, when I first heard that I did imagine a tree hanging out in a forest on a nice sunny day, and suddenly out of nowhere it literally explodes like a bomb, setting off a wildfire that destroys the entire state. That would be, well, admittedly kind of awesome (in the original meaning of the word), but that’s not what happens.
Here’s what it really means: eucalyptus trees are some of the most flammable trees on the planet -- scientists use an ignition rating of 1 to 10 with 1 being the most flammable. Eucalyptus earns a “1” along with grass. They are so flammable for a number of reasons: first of all, those smelly oils people like so much happen to be very, very flammable. So they are literally oozing accelerants. Additionally, they are extreme litterers. If left to their own devices, they will fill the forest floor below them with literal feet of bark and leaves and branches. To make things even worse, all that litter is also coated in oil, which prevents it from decomposing and make the litter EVEN MORE FLAMMABLE! Researchers are split on whether eucalyptus tolerate fire very well or if they actively fucking love it -- there’s a chance that the tree evolved the way it has because it benefits from wildfires that blast through the forest destroying everything but taking the eucalyptus’s seed pods and dropping them in newly fertile ground where they can start their lifecycle over again. Other scientists argue that the oil repels insects and the litter does other beneficial stuff and the fact that it leads to more wildfire is just a fun bonus for the tree. But everyone agrees that these trees are extremely flammable.
So when an existing fire hits them, they can dramatically “fwoosh” into flames in a way that can reasonably be described as an “explosion.” Here’s a video from Australia just last year showing a hint of how it looks, though note that when a wildfire is burning there are a lot of different things happening, like flames suddenly reaching a pocket of oxygen or behaving in weird ways when on slopes. It’s hard to find really good video of wildfires exploding like that because it’s fucking terrifying and the human holding the camera needs to run away very fast, and we don’t have any research where scientists have set fire to a stand of eucalyptus trees and filmed exactly what happens. But I challenge you to watch that video and argue that it doesn’t show something that qualifies as an “explosion.”
That said I do agree that when communicating the science of these wildfires to the general public, we probably shouldn’t say “trees explode,” and Trump’s comments and the resulting discourse show exactly why. I would bet money that some well-meaning scientist explained to Trump some of what I’ve just told you, and they used the word “explode” to mean “caught fire very quickly and dramatically.” And Trump walked away from that with the word “explode” and so he used it. What he said can be interpreted generously to be correct: trees can create litter that can act like a matchstick and when they catch fire they will dramatically light up and spread that fire. And I think that is what he meant because later he said “But if you did manage your forest, and if you removed all of that really dry and just — it’s like — “explosive” is the only word. You drop a cigarette on it, you come back a half hour later, and you have a forest fire. If you don’t have that sitting there, nothing is going to burn.”
And he’s not wrong! But it’s also worth noting that his comments are meant to spread the misinformation that these wildfires are only happening because of incompetent forest management on the part of the state of California. That is absolutely not true. He’s trying to downplay the fact that climate change contributed to this problem and will only keep making it worse by creating those dry conditions he’s talking about. He’s also trying to downplay the fact that the federal government owns and is responsible for the majority of California’s forests. All of these things can be true at once: individual human stupidity in the form of gender reveal parties started some of these fires, random weather events started some of these fires, climate change exacerbated these fires, poor forest management exacerbated these fires, planting highly flammable invasive trees exacerbated these problems, and terrible social policy has made it more difficult to get these fires under control.
So, do trees explode? It depends on what you mean by “explode.” Is Trump a science-denying narcissistic baby man who occasionally says things that are true? Yep.