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CNN REPORTER 1: I want to show you this picture out of Florida-- these pictures of a Burmese python.

ANNIE MINOFF: So we're looking at a CNN news clip from a few years ago.

ELAH FEDER: Yeah, a bit of soft news. A Burmese python was loose in the Everglades. And these snakes, these Burmese pythons are usually actually pretty good at hiding, but this one was bound to get noticed eventually.

ANNIE MINOFF: Because it was huge.

CNN REPORTER 1: 16-footer!

ANNIE MINOFF: It was the length of three people, he said, end to end--

ELAH FEDER: --ish, yeah.

ANNIE MINOFF: --and as thick as a telephone pole.

ELAH FEDER: Yeah.

ANNIE MINOFF: Local work crews spotted it hanging out by some trees, killed it with a shotgun, and then they noticed that it had this big bulge in the middle.

CNN REPORTER 1: They cut the stomach open. We won't show you that picture.

CNN REPORTER 2: Oh!

CNN REPORTER 1: I may tweet it if you want to--

CNN REPORTER 2: What was in it?

CNN REPORTER 1: A deer.

CNN REPORTER 2: Oh!

CNN REPORTER 1: Yeah. Like a 70-pound deer.

CNN REPORTER 2: That thing ate a deer?

CNN REPORTER 1: That's right.

CNN REPORTER 2: I do not like snakes. I do not like snakes.

CNN REPORTER 1: Look at the size of that thing!

ELAH FEDER: Burmese pythons-- you might guess this from the name-- come from Southeast Asia.

ANNIE MINOFF: We actually brought them over as pets. And the story goes that during Hurricane Andrew, baby snakes escaped from a breeding facility, which sounds like a horror movie, and they found that they could survive pretty nicely out in the Florida Everglades. And these things are really scary.

ELAH FEDER: Yeah. There are videos where alligators try to attack these things and the snakes, the pythons, are like, no, I am going to eat you. I'm going to eat you, the alligator.

ANNIE MINOFF: So Burmese pythons might feel like an especially dramatic case, but chances are you've actually heard a story like this before.

We move a species from one part of the world to another part of the world by ship, by plane, by accident, maybe on purpose. Anyway, a species shows up someplace new, and if it ends up doing really well in its new home--

ELAH FEDER: Like too well. Like so well that it causes economic health or ecological problems--

ANNIE MINOFF: --then we call that species an invasive species.

ELAH FEDER: Right. We've heard so many stories like this. Emerald ash borers chewing up ash trees, Asian carp crowding out native fish in the Mississippi. White nose syndrome, it's a fungus that came from Europe. It's killed over 6 million bats. This kind of thing is happening all over the world. But in the United States alone, thousands of new species have come in-- plants, insects, viruses, mammals, and the consensus seems to be, yeah, non-native species are bad news.

NATIONAL GEOGRAPHIC ANNOUNCER: A storm is gathering on the horizon.

[SUSPENSEFUL MUSIC]

An invasion, decades in the making, is underway. An alien species is staking claim to the Americas.

ELAH FEDER: National Geographic really driving this message home, that foreign species are invading. Species like--

NATIONAL GEOGRAPHIC ANNOUNCER: A killer bee.

ELAH FEDER: --zebra mussels--

NATIONAL GEOGRAPHIC ANNOUNCER: The snakehead.

ELAH FEDER: --chestnut blight.

[SCREAM]

NATIONAL GEOGRAPHIC ANNOUNCER: Asian carp invasion.

ANNIE MINOFF: Ah, all right. So what I am getting from this voice is that an army of bees and fish are swarming in, they are going to murder us all in our sleep.

ELAH FEDER: Mhm.

ANNIE MINOFF: Though to be fair, this is actually how National Geographic says beaver.

NATIONAL GEOGRAPHIC ANNOUNCER: Beaver.

[OMINOUS MUSIC]

ANNIE MINOFF: So nature documentaries are always going to hype this stuff up. But it's a problem people do take very seriously. The federal government has spent billions of dollars fending off these non-native species, on trapping and poisoning and burning them. But some people think it's all based on a flawed premise.

FRED PEARCE: I began by thinking about alien species like most of us do, as kind of a bad thing. These foreign species coming in and taking over our ecosystems.

ANNIE MINOFF: Fred Pearce, an environmental journalist.

FRED PEARCE: But the more I looked into it, the more I began to think that's a kind of phony story.

ELAH FEDER: Fred is not alone in this. There are other people, some ecologists included, who think we're getting all worked up about species that aren't really hurting us, and that what's driving the war on non-native species, it isn't science, it's prejudice.

ANNIE MINOFF: Of course, a lot of scientists and environmentalists completely disagree.

ELAH FEDER: Today on Undiscovered, the fight between environmentalists over one particular species. It's a tree. It's not one you would guess would be especially controversial.

ANNIE MINOFF: No.

ELAH FEDER: But in the Bay Area, some people are saying it's putting lives at risk, that it could kill people, that it maybe already has. So they're going after these trees. They're chopping them down. They're poisoning stumps. They are trying to protect themselves.

ANNIE MINOFF: And other environmentalists are doing whatever they can to stop them. That's coming up.

ELAH FEDER: Eucalyptus trees. On the face of it, they're pretty inoffensive. They're even likable.

ANNIE MINOFF: They're tall with bluish gray leaves. One could say majestic.

ELAH FEDER: One could say.

ANNIE MINOFF: And they smell like minty? Lemony? Kind of medicinal.

ELAH FEDER: Yeah. Definitely not scary like pythons, right? They're trees. But according to some people, eucalyptus trees are dangerous in their own way. And if you want to see just how bad they can get, Norman La Force says you just have to look at what happened in 1991.

NORMAN LA FORCE: OK, I'm pretty sure it started down in that area there. You see those two round tower things--

ELAH FEDER: Yeah, yeah.

NORMAN LA FORCE: --to the right of that?

ELAH FEDER: I was standing with Norman on the outskirts of Oakland, just by the side of a road. We were looking downhill at a clump of houses. The sun had almost set. This beautiful white fog was rolling in.

NORMAN LA FORCE: That's amazing. That's really pretty.

ELAH FEDER: It was getting pretty dark, but I could still kind of make out what Norman was pointing to. There was a slope behind one of the homes. That's where he thinks the fire started.

ANNIE MINOFF: It was Saturday, October 19, 1991, around noon. The day was warm and dry, but it wasn't too windy. So by evening, crews thought they had the fire under control.

ELAH FEDER: They kept coming back to check throughout the night, but everything looked good. You know, the situation seemed handled. You probably know where this is going.

SPEAKER 5: Here is the latest information that we have on the fire right now. Five fatalities, nine injuries, mostly injuries from smoke inhalation in that area. The mayor of Oakland--

ANNIE MINOFF: Around 11:00 the next morning, while firefighters were sweeping the area for lingering hot spots, The fire reignited. And this time it was not so easily contained. Within half an hour, people were evacuating their homes.

[SIRENS]

ELAH FEDER: Pretty soon the roads are clogged and traffic is barely moving. The situation's devolving.

SPEAKER 6: --understand they gotta leave. They gotta leave their cars here.

ELAH FEDER: In this video, a man is running between the cars urging people to get out.

SPEAKER 6: Shut them off and leave your cars and walk. All right.

ANNIE MINOFF: He's talking to a woman in the front passenger seat who's just weeping with her hands on her face. On the side of the road, the fire is burning in these wild billowing waves. Then the video cuts to people who are already on foot, weaving past standing cars.

ELAH FEDER: By the time officials declared the fire over two days later, it had consumed more than 3,000 homes and killed 25 people. At that point, it was the worst fire in California's history.

During the 1991 fire, Norman La Force was living in the hills. Norman was the guy who was showing me where the fire started.

NORMAN LA FORCE: I was actually out campaigning that day because I was running for election to El Cerrito city council.

ANNIE MINOFF: El Cerrito is a small city in the East Bay hills. And this was Norman's first time running for a seat. So of course he's going door to door, he's introducing himself, and that's when he smelled smoke.

NORMAN LA FORCE: Saw embers coming down and realized there was a fire.

ANNIE MINOFF: The fire didn't end up reaching Norman's neighborhood, and his house was fine, and he won that city council seat.

ELAH FEDER: But Norman La Force wasn't about to sit back on the sidelines on this issue. He is one of these people who gets involved in everything, not just city council. He's active in his local Sierra Club chapter. He's founded environmental groups himself. His name pops up in the local newspapers pretty regularly. And like a lot of people, Norman wanted to know how this fire got so out of control.

ANNIE MINOFF: The FEMA report printed out a few reasons, including hot, dry seasonal winds and five years of drought. Two big factors that of course they couldn't control. But Norman and other locals zeroed in on something that they could control-- eucalyptus trees.

NORMAN LA FORCE: It was quite apparent, after reading about everything and seeing it, that eucalyptus trees are very fire dangerous.

ANNIE MINOFF: Eucalyptus trees are from Australia. Californians brought them here on purpose in the 1850s. And over the next few decades, they planted these trees enthusiastically, mainly the blue gum eucalyptus.

ELAH FEDER: And if you read newspapers from the time, you would think the blue gum was the Giving Tree. It was just good for everything-- for lumber, windbreaks, shade, and medicinal oils, and just for being pretty.

CHARLES BERGQUIST AS REPORTER: Always green. It charms the eye at every season of the year. It is tall, live, and graceful. To behold it swaying in the passing breezes is to behold the poetry of motion.

ELAH FEDER: I mean, it's a fine-looking tree, but poetry of motion?

ANNIE MINOFF: [LAUGHS]

ELAH FEDER: That's strong.

ANNIE MINOFF: Yeah, that was from a particularly gushy op-ed from 1907 urging people to plant even more eucalyptus. Well, turned out eucalyptus from those plantations, the lumber was kind of terrible. It split and it warped. But it was too late. Eucalyptus was all over California.

ELAH FEDER: Now all trees, any vegetation can catch fire, and eucalyptus trees were not the only thing that burned in 1991. But there are a couple of things that make these trees especially worrying for some people. First, they are oily.

ANNIE MINOFF: The oil is actually what gives them that kind of minty smell.

ELAH FEDER: And they also shed a lot of bark and leaves, even branches. They drop all that on the ground and form a thick litter bed, which means that there's potentially a lot of fuel to burn.

ANNIE MINOFF: So for Norman, the solution to this seems obvious. Cut down the dangerous Australian trees. Let native vegetation grow back.

ELAH FEDER: And this idea, it's gained real traction. The Bay Area has cut down thousands of these trees over the past few decades. And they might have removed a lot more if it wasn't for this guy, Dan Grassetti.

DAN GRASSETTI: I've lived in Berkeley Oakland Hills since I was 13, and I'm 63 now. So 50 years.

ELAH FEDER: I met Dan at his house last fall. And while we were talking, his kitten Tony was snuggled up, kept batting at the microphone.

ANNIE MINOFF: Aw, Tony.

ELAH FEDER: You're gonna hear Tony. Anyway, while Dan and I talked, I was looking out his living room window at this green hillside.

DAN GRASSETTI: Yeah, I'm really fortunate to be-- Tony-- very fortunate to be looking out at an area that is guaranteed to not be developed.

ELAH FEDER: It really was lush and green. And this is the landscape that Dan's known since he was a kid. Eucalyptus have always been a really big part of that. But then--

DAN GRASSETTI: There was one fateful summer day while I was riding my motorcycle down Claremont Avenue, and I had to stop because there were trees falling across the road. And I parked the bike, got off, and I went up to the person who seemed to be responsible, and I asked, what are you doing? Who's doing this?

ANNIE MINOFF: It turns out it was a local volunteer group who'd gotten a grant to cut down eucalyptus trees. Dan doesn't remember getting a particularly good reason for why.

DAN GRASSETTI: So the discussion quickly went downhill.

ELAH FEDER: So Dan starts investigating. And over time, he learns it's not just this spot on Claremont Avenue. Eucalyptus trees are being targeted all over the Bay Area.

ANNIE MINOFF: And pretty soon, Dan is one of the loudest opponents of eucalyptus clearing. Asking basically, can you really prove that these trees are dangerous? Like, do you have the science to back that up? Or do you have something else against them?

ELAH FEDER: So Dan forms the Hills Conservation Network, a little volunteer group with a mission to preserve these forests. They only have a few members, but they're very ambitious. In 2015, they actually sue the federal government over plans to clear eucalyptus in the hills. They say this is just bad fire management strategy. And the government actually backs down. They settle with Dan's group, they pull funding from two big tree-cutting programs. This is a major win for team eucalyptus.

DAN GRASSETTI: It was effing amazing.

ELAH FEDER: Other people not as pleased. Norman, the guy who gets involved in everything, a lot of his activism is with the local Sierra Club. And they had actually sued the government over these plans, too, except they wanted the opposite from Dan's group. They wanted even more trees cut down.

ANNIE MINOFF: Poor government can't get anything right.

ELAH FEDER: No. Anyway, they lost that battle to Dan.

ANNIE MINOFF: And the thing about Dan that I think is interesting is it's not like he's one of these, like, bleeding-heart tree lovers who just cannot stand to see a single tree cut down. He just doesn't buy that eucalyptus trees are all that dangerous, that they are the reason the Bay Area burned so badly in 1991. He thinks people are just pinning the blame on them.

ELAH FEDER: You're saying that they're basically being scapegoated in the fire debate?

DAN GRASSETTI: I think they're being used as a-- yes, they're being scapegoated. They're being used as a way to advance an agenda, using funds that were intended for something else.

ELAH FEDER: Coming up, one possible agenda. And what Nazis have to do with invasion biology.

 

ELAH FEDER: Most of the stories that we hear about non-native species are not happy ones. Some of them are downright terrifying. But here's another story. It's from Puerto Rico.

A few decades ago, people in Puerto Rico started moving to cities. They were abandoning farmland, farmland that had once been forest.

FRED PEARCE: Now a great chance for nature to recover.

ANNIE MINOFF: Fred Pearce again, the environmental journalist we heard from earlier.

FRED PEARCE: Well, the local species couldn't do it.

ANNIE MINOFF: After all those years of farming, the soil was really badly eroded. And a lot of native plants just could not grow in it. But a foreign one-- the African tulip tree-- could.

FRED PEARCE: Suddenly the African tulip started spreading across Puerto Rico into the abandoned farmland. Then native birds started nesting in the branches of the African tulip.

ELAH FEDER: And more species came-- frogs, bats, insects. Most of them were native to Puerto Rico. Some of them weren't. But they were all living together, creating this new kind of ecosystem.

ANNIE MINOFF: So you could see that as a foreign tree invading, but from Fred's perspective, this is just nature taking over. It's just not the same nature that was there before.

ELAH FEDER: Dan with the kitten?

ANNIE MINOFF: Classic. Invasive species, by the way.

ELAH FEDER: That is true. Anyway, Dan says some people are against eucalyptus trees because they have this idea that eucalyptus just doesn't belong here. They're not from California. They weren't here until relatively recently. But this is one of the points that people like Fred are always making.

FRED PEARCE: Nature is always changing. Species are always moving in and out.

ELAH FEDER: Case in point. 13,000 years ago there were camels roaming North America.

ANNIE MINOFF: Camels.

ELAH FEDER: I didn't know this. The camels that are in other parts of the world today, their ancestors actually came from here. So species are always moving. Nature is always changing. Who is to say which species are properly native and belong here and which ones don't? That's the argument, anyway.

ANNIE MINOFF: And that might sound kind of abstract, like nature is change. But there are actually plenty of non-native animals and plants that we do like and that we actually depend on. They're just so familiar that we have stopped thinking of them as, quote unquote, "aliens." Cows, honeybees, wheat, soy, and chickens, like much of American agriculture comes from other parts of the world.

ELAH FEDER: Right. So this idea that outsider species are bad, that we shouldn't let them in, what is that actually about?

FRED PEARCE: I mean, the ecologists will hate me for saying this, but I think they are being xenophobic about this.

ANNIE MINOFF: Xenophobia, which, by the way, is not just a fear of foreign people. It can be a fear or hatred of anything foreign.

FRED PEARCE: There's an assumption that foreign species are bad in the same way that, you know, some illiberal people, if you like, make an assumption that foreign people are bad.

ELAH FEDER: Remember how Nat Geo talks about invasive species?

NATIONAL GEOGRAPHIC ANNOUNCER: An alien species is staking claim to the Americas.

ANNIE MINOFF: Some ecologists sound a whole lot like that, actually. One leading researcher once warned that a growing army of invasive species was overrunning America, and that, quote, "every part of the United States is under attack."

ELAH FEDER: And it's not just Fred who is accusing ecologists of being xenophobic. Historians, philosophers have made this accusation, even ecologists.

One of the most outspoken critics is an ecologist named Mark Davis. And he told me, yeah, this is basic xenophobia. This is us versus them. It's just how we like to divide the world.

ANNIE MINOFF: Of course, if you call somebody xenophobic or suggest that their views are somehow prejudiced, they're going to get their back up. Take what happened to a couple of years ago. Dan and Norman were invited to this local synagogue to talk about the eucalyptus question. Here is how Dan, our eucalyptus defender, started off.

DAN GRASSETTI: I wanted to start off with just a brief something to think about, and this concerns this whole native versus non-native business. So how did I get here? It turned out that my parents had to leave Europe in the early '40s because a gentleman by the name of Adolf Hitler was killing off all our relatives. And as a result of that, they became invasive species. They came to the United States and they produced me and three others, and now we're invasive species in this land.

ELAH FEDER: Now, as this is happening, Norman, he has his hands clasped in front of him and he's looking down, just fidgeting with his thumbs. And when Dan says Adolf Hitler, Norman does not say a word. But for a few moments he stops fidgeting. He looks frozen. But eventually it's his turn to talk.

NORMAN LA FORCE: And I really resent-- I have to say this, I'm sorry. I really resent the implication that I am somehow connected with the Nazis because I want to see a restoration.

ELAH FEDER: It's a widely understood principle of debates that if you mentioned the Nazis and suggest that your opponent is somehow aligned with Nazi thinking, you're very unlikely to have a productive conversation.

ANNIE MINOFF: Unless you are actually dealing with neo-Nazis or white supremacists.

ELAH FEDER: Right. But Dan, he's not just making this up. There actually is a Nazi connection here. It's a connection that haunts invasion biology because people will keep bringing it up. Michael Pollan in a 1994 "New York Times" op-ed, Stephen Jay Gould in an essay that he wrote just a few years before he died, Fred, the journalist we talked to, he wrote about it in his book too.

ANNIE MINOFF: So here's the connection. We know Nazis were obsessed with so-called racial purity. But some in Nazi Germany were also obsessed with purifying the land. A leading government botanist wanted to, quote, "cleanse the German landscape of unharmonious foreign substance. In 1942, German botanists compared the fight against Impatiens parviflora--

ELAH FEDER: Which is just a little plant with yellow flowers.

ANNIE MINOFF: --to the fight against Bolshevism. They called it the Mongolian invader, and demanded a, quote, "war of extermination."

ELAH FEDER: Michael Pollan in his "Times" piece, and Fred when I talked to him, they were pretty clear that, no, they're not saying that people who want non-native plants gone are secretly fascists or Nazi sympathizers. Even Dan, in that same debate where he brings up the Nazis, he says there's nothing inherently evil about native plant restoration. Still, for ecologists, these Nazi mentions, the xenophobia accusations, it's all pretty exasperating.

SARA KUEBBING: Yeah, the xenophobia argument, just from personal level-- it's not where I'm coming from and it's not where I think invasion science is coming from. It's not this fear of the other.

ANNIE MINOFF: Sara Kuebbing is an assistant professor in the biological sciences department at the University of Pittsburgh.

ELAH FEDER: Sara is an invasion biologist and her research is all about what non-native plants are doing to ecosystems. And no surprise, she says her field is not prejudiced against non-native species. She says there are real reasons that we worry about them, because in ecosystems, newcomers act very differently from the locals.

SARA KUEBBING: Non-native species are different because they are dropped into a place without any of the other species that they've co-evolved with. Which, for a lot of them, is probably a difficulty if you don't have the pollinator to pollinate your flowers or you don't have a disperser to disperse your fruits.

ANNIE MINOFF: A fungus to hook your roots up with nitrogen. These are mutualistic species, right? The good guys who helped you survive and reproduce back in your homeland. And maybe that's why a lot of non-native species, they end up being pretty harmless. They show up, but they don't have their friends around them. They don't have their co-conspirators. Or the climate just isn't quite right and they end up not doing that great.

ELAH FEDER: But--

SARA KUEBBING: But you also might be missing a lot of the bad guys that sort of keep you in check.

ELAH FEDER: Which could explain what happened with the emerald ash borer. When it landed in North America, it had this big, tasty buffet of ash trees in front of it. But it had left most of its predators and parasites back home, so it didn't have much holding it back, which is terrible for ash trees.

ANNIE MINOFF: And that is real. It is not xenophobia to want to stop a beetle, to want to save ash trees. For Sara, that's just basic stewardship.

ELAH FEDER: Talking to Sara and to Fred, who has been criticizing her field, it seemed like their differences were less about the facts than about emphasis.

ELAH FEDER: Like Fred, he's with Sara on this. He says, yes, some non-native species do cause problems and it's legitimate to care about those problems, to worry about it, to want to do something. He just wants to remove this assumption that all non-native species are bad.

ANNIE MINOFF: Like across the board.

ELAH FEDER: Right. And Sara, she never claimed they all were, but she doesn't want to take the risk given that some are. So in the end, regardless of which side you're on, it's pretty clear that when we're trying to decide how good or bad a particular species is, we can't just ask, is it from here? We have to look at species on a case-by-case basis.

ELAH FEDER: Which brings us back to the debate that started all of this for us-- eucalyptus trees.

ANNIE MINOFF: Right. Eucalyptus trees.  

ELAH FEDER: Norman says that they are dangerous. Dan says there isn't good evidence to back that up. What does the science say?

ELAH FEDER: I really, I really wanted to get to the bottom of this.

ANNIE MINOFF: Yeah.

ELAH FEDER: So I read up on it. I contacted wildfire experts.

ANNIE MINOFF: Eight wildfire experts.

ELAH FEDER: Mhm. And most experts told me that eucalyptus trees are a serious fire hazard.

ANNIE MINOFF: Hallelujah for an answer.

ELAH FEDER: It's-- yeah, it's more complicated.

ANNIE MINOFF: I know it is. It always is.

ELAH FEDER: There was a major exception. Dave Maloney, he's actually a retired firefighter and fire investigator. He is like one of the loudest defenders of the eucalyptus trees.

ANNIE MINOFF: In like the lineup of like, you know, six out of seven dentists recommend, he's like--

ELAH FEDER: He's--

BOTH --the seventh dentist.

ELAH FEDER: Right. He was saying to me, sure, you've got these people telling you that eucalyptus trees are dangerous. But what are these claims based on? What is the actual evidence? And the truth is, I didn't have the evidence that I was looking for-- a nice, comprehensive study that looks at all the factors that go into fires. Litter beds, oil and moisture content--

ANNIE MINOFF: Flame lengths.

ELAH FEDER: --flame lengths. Yep, you heard me talking about that.

ANNIE MINOFF: So much about flame lengths.

ELAH FEDER: We have pieces, but we don't have a study that adds up all those factors, tells us how hazardous blue gum eucalyptus trees are, and then compares them to native California vegetation, right? Because that stuff burns too, and you need to know--

ANNIE MINOFF: Compared to what.

ELAH FEDER: Right, compared to what-- what is actually worse? But it left me really frustrated because I had expert opinion, that's worth a lot, but it was mixed and I didn't have a study to back up what they were saying.

ANNIE MINOFF: And that's frustrating. But I feel like maybe it's time to step back a little bit. Fire is obviously a problem throughout California and it's one we've been hearing about more and more. This year and last California broke records for the largest and most destructive fires in its history. And with these fires no one’s pinning the blame on eucalyptus trees. They’re blaming houses built right up against all of that very flammable wilderness. They’re blaming powerful winds that dried out vegetation.

ELAH FEDER: Like the weather. Basically the weather.

ANNIE MINOFF: The weather and also climate change. Like you can’t pin any one fire on climate change but big picture you also can’t talk about California’s fire problems without talking about climate change. In other words -- California’s fire problems, they are so much bigger and more intractable than its trees.

[MOTOR RUNNING, BIRDS]

ELAH FEDER: But on a few dozen acres in the East Bay hills, not far from Dan Grassetti's house, a group of volunteers is still trying to create a eucalyptus-free zone. It's actually the same group that Dan saw all those years back, cutting down trees by the road--the Claremont Canyon Conservancy. There's still plenty of eucalyptus trees in the hills, but they've carved out this little native plant oasis. And they're making sure that eucalyptus stays out.

TOM KLATT: See that tall thing back there? Does that look like a euc to you, John? There's a 15-foot tall eucalyptus tree just off the trail--

ELAH FEDER: All I see is this pale, greenish-gray thing. It's totally blending in with the rest of the leaves and the branches. But Tom Klatt, he has an eye for this. He's a retired environmental land manager from Berkeley. And he dives right in, crawls through the bush till he reaches that euc, saws it down, dabs on a few drops of herbicide.

TOM KLATT: Yes, you got it. Hooray! Another euc has bit the dust. We found--

SPEAKER 7: Tom must be here.

TOM KLATT: Yes. This is the fourth euc.

SPEAKER 7: Oh, he's got a good eye because--

SPEAKER 8: Tom has a very good eye.

ELAH FEDER: Tom ends up nabbing eight eucs in just a few hours. And the volunteers are clearly very impressed with his haul. They told me, no, this will not stop fires from happening altogether, but having fewer eucs in general, they think it'll make them safer. But there are limits to what they can do. Even here, with all their hard work, eucalyptus are not giving up so easily.

ELAH FEDER: Is that a giant eucalyptus tree?

TOM KLATT: Yes.

ELAH FEDER: Yeah, just before we headed back to the road, I see this enormous eucalyptus tree just looming over the south side of the restoration grounds.

TOM KLATT: But unless you have $10,000, it's gonna stay there.

ELAH FEDER: That would cost $10,000 to remove?

TOM KLATT: Because it's in a very remote area. The road is right over there, but to get to this tree you'd have to go down and then come back up with huge chainsaws.

ELAH FEDER: Yeah, cutting down that one tree would cost thousands. It might be especially expensive, but cutting down big old trees is never cheap. And there are millions of eucalyptus across California.

TOM KLATT: So we'll just leave that one there.

ELAH FEDER: More than a century ago, Californians brought eucalyptus seeds from the other side of the world. They planted them across 40,000 acres for shade, for beauty, for a lumber industry that never took off. Now they've grown up into big old trees, and they're firmly rooted. Like it or not, for these Australian trees, California's home.

ELAH FEDER: Undiscovered is reported and produced by me, Elah Feder--

ANNIE MINOFF: And me, Annie Minoff. Our senior editor is Christopher Intagliata and our composer is Daniel Peterschmidt. Our production intern is Kaitlyn Schwalje. We had fact-checking help for this episode from Michelle Harris. I Am Robot And Proud wrote our theme.

ELAH FEDER: Thank you to the whole Science Friday staff as always. And also thank you to Ray Madrigal who videotaped the synagogue debate and let us use his audio. Finally thank you to the many people on both sides of this issue who spent hours talking to me, taking me for nature walks, and providing me with documents. There is so much more to this issue. We barely scratched the surface so we have some links up at our website if you’d like to learn about the science and history of invasion biology or about eucalyptus trees--

ANNIE MINOFF: Find that at UndiscoveredPodcast.org. UndiscoveredPodcast.org. And we'll see you next week.

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