How and why do trees get so old?

Daniel and Kelly talk about the science behind aging trees, and why some trees live so long. See omnystudio.com/listener https://omnystudio.com/listener for privacy information.

Speaker names marked ? are inferred from speaking time and the show’s known hosts — they are not voice-verified.

• 0:00Daniel Whiteson?

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• 2:11Kelly Weinersmith?

  The oldest tree we know of is Methuselah, a Great Basin bristlecone pine that is almost 5,000 years old. Methuselah began putting down its roots during the age of the pyramids in ancient Egypt. It also lived through the rise and the fall of ancient Greece and ancient Rome as well. Hammurabi, Nefertiti, Buddha, Pythagoras, Confucius, Socrates, Alexander the Great, Cleopatra, Genghis Khan, Joan of Arc, Da Vinci, Copernicus, Ivan the Terrible, Shakespeare, Pocahontas, Newton, Hamilton, Mozart, Napoleon, Lincoln, Darwin, Nightingale, Pasture, Edison, Gandhi, Hitler, Parks, Mandela, Martin Luther King Jr., and Betty White.

• 2:54Kelly Weinersmith?

  Generations of humans have struggled and strove, some making the world better, some making it worse, but all of them lived out their entire lives in just a sliver of the time during which Methuselah has been patiently growing in the White Mountains of California. There's something both bewildering and awe-inspiring about incredibly old trees. And today, we're going to be talking about what we know about them. How do we age trees? And how and why do some trees live so long? Welcome to Daniel and Kelly's extraordinarily tremendous universe.

• 3:44Daniel Whiteson?

  Hi, I'm Daniel. I'm a particle physicist, and I round myself up to 50 years old.

• 3:50Kelly Weinersmith?

  Hello, I am Kelly Weiner-Smith. I study parasites and space, and I round myself down to 40. You're even older than I am than I had realized, Daniel.

• 4:03Daniel Whiteson?

  Wonderful thing to hear.

• 4:05Kelly Weinersmith?

  It's all about how you round. Although, you know, I thought we had both agreed that we round up on average, but at only 42, I think I'm going to go ahead and round down.

• 4:13Daniel Whiteson?

  Yeah, no, I think that's fair. Who really needs more significant digits than one, right?

• 4:17Kelly Weinersmith?

  That's right. That's right. Do you have a favorite tree?

• 4:23Daniel Whiteson?

  Do I have a favorite tree? I love the redwoods, you know, out here in California. I gotta say, that's something spectacular about California and the mystery, the majesty of being the presence of these super tall and super old beings and thinking about all the things they've seen, experienced. I love it. I just love old trees in general. Like when you drive down a street in a neighborhood that's like 100 years old and the trees like cross over the street or have all these wiggles and branches, whereas like a new suburb with these like tiny little potted plant trees is just a little sad. So, old trees are wonderful because it's something you gotta earn. It just takes time. You know, you can't like fast grow a tree to a huge size.

• 5:03Kelly Weinersmith?

  I totally agree. When I lived in California, I had to go see the redwoods and I realized that I'd been like looking up at one of those trees with my mouth open and I was like so glad nothing had fallen into it because it was just like, I must have stood there for, you know, 15 minutes just looking at the same tree being like, oh, the things that you've seen or, you know, have been alive through. It's just incredible. And then I had the great pleasure of working at Rice University for a while, which I know is where you did your undergrad. And they've got that running track around the outside of the university that is surrounded by live oaks. And they're the ones that have those like tortuous arms that like go back, they down, they touch the ground, they come back up again. Oh, they're so gorgeous. I actually don't know how old those live oaks are, but there's something about a big tree that I love.

• 5:47Daniel Whiteson?

  Yeah, and Rice has so many trees. I think there's something in the charter that they have to have more trees on campus than students. So they really preserve the trees on the campus.

• 5:56Kelly Weinersmith?

  I can't believe they've got more trees on campus than students. If so, they gotta shut that place down, man. I don't think that's working out.

• 6:05Daniel Whiteson?

  Well, I gotta ask you, Kelly, the obvious question. Given California's redwoods and the majesty of our old trees, what does Virginia have to compare? I'm giving you an opportunity here.

• 6:15Kelly Weinersmith?

  Oh, my God, this is easy. So California is beautiful, but have you been to Shenandoah National Park?

• 6:21Daniel Whiteson?

  Oh, I have. Land of many uses.

• 6:24Kelly Weinersmith?

  Many uses? What do you mean? Like, you're gonna cut my trees down?

• 6:28Daniel Whiteson?

  No, I just remember camping in the Blue Ridge Mountains one time, and there was a sign when you enter, it's like, welcome to the Blue Ridge Mountains, land of many uses. And I'm like, hmm, I wonder what that means?

• 6:38Kelly Weinersmith?

  Yeah, I don't remember seeing that on the sign. But like, you've gone camping in the Blue Ridge. The answer is obvious. It's just so gorgeous, seeing all of those rolling hills with all the trees and the like mist coming up over them in the mornings and seeing the sunset. There's like no more beautiful view in all of the United States than what you get. I'm laying down the gauntlet, man.

• 6:59Daniel Whiteson?

  I was with you up until that point. I mean, I like the Blue Ridge Mountains. For mountains, they're cute. I mean, they're not that tall or that pointy.

• 7:07Kelly Weinersmith?

  That's why they're so nice to walk.

• 7:10Daniel Whiteson?

  I like a nice granite topped mountain, you know, like above the tree line. That's my jam. The Sierras, for example. Oh, yeah. And I just don't think you can compare to the majesty of the coastal redwoods, you know? Nothing stands up to that, in my opinion.

• 7:24Kelly Weinersmith?

  Those are beautiful. I'll give you that. I don't feel like I want to pit one natural beauty against another. But, but I can say that in grad school, I tried hiking White Mountain, where the bristlecone pines are. So we talked about Methuselah in the opening. And, you know, I was climbing up there and the air was getting thin. And I was like, ugh, feeling miserable. And, you know, so no, give me Shenandoah any day where I can breathe. It's like, I don't want to go to space. I don't want to go to White Mountain.

• 7:49Daniel Whiteson?

  Yeah, no, it's beautiful. Absolutely. I'll give you that. And you're right, we shouldn't pit one against the other. There's lots of different ways to be beautiful, and we should appreciate all of it.

• 7:57Kelly Weinersmith?

  Amen. All right. And so we had this absolutely incredible question from a listener's son about old trees. And that's what we're going to be talking about today. But before we listen to the question, I want to remind you that you can send us your questions, or you can send us your kids' questions at [email protected].

• 8:18Daniel Whiteson?

  We really love hearing from you, and we love hearing from your kids. Thank you to everybody who listens to the pod with your kid. It's a great way to start conversations about science.

• 8:27Kelly Weinersmith?

  Yay. All right, so let's hear the question that we're chatting about today.

• 8:30Daniel Whiteson?

  Hi, Daniel and Kelly. I have a question. Why do some trees live longer than other trees and why do they live longer than people? This is a great question because this is a question I've had since I was a kid looking at those redwoods and wondering like, why do they live so long? How do they live so long? What's going on?

• 8:50Kelly Weinersmith?

  Yeah, it's a fantastic question. And it was one where, when I listened to it, I thought, oh, this is another one where I don't really know the answer. And so I was thrilled to have an opportunity to do some research. And so let's start this conversation by talking about how we even go about aging trees in the first place. I think a lot of us are familiar with the idea that you can age trees based on their rings, but it's a little bit more complicated.

• 9:13Daniel Whiteson?

  So you can't just chop down the tree and count the rings?

• 9:16Kelly Weinersmith?

  Oh, Daniel. Yes, but then you're a monster.

• 9:24Daniel Whiteson?

  Well, that reminds me of that Far Side cartoon where the guy is standing there with his son and axe and he's chopped down some big tree and he's going through the history of the tree, all the things the tree has survived until, of course, that day that he chopped it down.

• 9:35Kelly Weinersmith?

  Right, but it couldn't survive us. That's sad.

• 9:39Daniel Whiteson?

  So tell me then, how do we know how old a tree is without chopping it down and counting its rings?

• 9:44Kelly Weinersmith?

  Well, for a while there, we were using relational ages. So you would say, oh, well, the tree was planted around the time the Parthenon was built or something like that. And so Pliny was using these relational ages where he would age trees based on historical stuff that was happening at the same time.

• 10:00Daniel Whiteson?

  But how would you know what historical stuff is happening at the same time? How would you know this tree was planted at the same time as the Parthenon or something?

• 10:06Kelly Weinersmith?

  I think records and institutional memory. But you're right. I mean, you don't know unless somebody happens to know, local knowledge.

• 10:15Daniel Whiteson?

  And that you can trust that knowledge.

• 10:17Kelly Weinersmith?

  Yeah, I bet they got a lot of ages wrong. That can't work great.

• 10:21Daniel Whiteson?

  I mean, I'm sure there's a lot of mythology, right? People like this tree is thousands of years old. And because people are bad at deep time, you know?

• 10:28Kelly Weinersmith?

  Oh, my gosh, so bad. And I was reading this book called Elder Flora. And it talks about sort of the history of our relationship with old trees and how we often get the ages wrong and how trees become important for religious ceremonies and stuff. So anyway, anyone who's interested in old trees, that's a good book worth checking out. But towards the end of the 19th century, and I'm surprised this wasn't common earlier, we started getting a handle on aging trees by counting their rings. So let's talk about the science behind where these rings come from.

• 10:58Daniel Whiteson?

  Yeah. Why do trees have rings and why do they have one ring per year anyway?

• 11:02Kelly Weinersmith?

  Yeah, right. Great question. Why doesn't the inside of a tree all look the same?

• 11:06Daniel Whiteson?

  Yeah, I mean, I don't have rings. If you cut me open, you couldn't count my age.

• 11:10Kelly Weinersmith?

  Well, we don't really know until we try.

• 11:15Daniel Whiteson?

  Maybe we should start with a core sample.

• 11:17Kelly Weinersmith?

  That's right. Yes, that's right. I'll get out my increment borer, but we'll get to that. So, so here's how trees grow. All right. Say you do, do the horrible act of cutting down a tree, which of course sometimes you have to do, and we all use paper. So anyway, no judgment. So you cut down a tree. You're looking at the center of a tree. The center part of the tree is called heartwood. And if it's a big tree, that center part is actually dead.

• 11:40Daniel Whiteson?

  What? Why is it called heartwood if it's dead?

• 11:43Kelly Weinersmith?

  Trees are weird, and that's going to be the theme of today's show, I think, is that trees are weird. And so, you know, the listener wanted to know why humans don't live as long as trees. And I think the answer is trees are weird. And, you know, I'll do a better job of answering that at the end of the episode, but that's the take home point. So the center is dead and it's dead because it no longer has access to water and nutrients that are coming up through the xylem, which we'll get to. So the next level you've got is the sapwood. And the sapwood is the level where you still get water that's coming up through the xylem. So you've got essentially, I think of it as like a series of tubes, but it's really like specialized cells that go from the roots up through the trunk of the tree and into the canopy.

• 12:25Kelly Weinersmith?

  And so the sapwood is getting access to that water and to the nutrients. Next to the sapwood is the cambrium. And the cambrium, maybe the cambrium, we all know how good I am at pronouncing things, is going to be very important for the rest of this episode. So this is the layer where you have the growth happening. So on one side, towards the outside of the tree, the cambrium starts producing bark. And that bark is going to build up over time and that's going to protect the tree. Towards the inside of the tree, it's producing the sapwood. So it's producing more of that like woody tissue that you would build a house out of, for example.

• 13:04Daniel Whiteson?

  Woody tissue, otherwise known as wood?

• 13:06Kelly Weinersmith?

  Yeah. Well,

• 13:08Daniel Whiteson?

  For us layfolk.

• 13:09Kelly Weinersmith?

  But wouldn't bark be woody tissue kind of also? I don't know. But you wouldn't necessarily build the house out of bark. So I was trying to be a little more specific, but.

• 13:17Daniel Whiteson?

  Yeah, well, I don't want to blow my nose on a woody tissue. So I guess it has lots of meanings.

• 13:20Kelly Weinersmith?

  That's right. That's right.

• 13:22Daniel Whiteson?

  Well, before you dig deeper, my first question is like, are these hard divisions? Is there like an edge between the heartwood and the sapwood? Or is it like a spectrum where like in the middle, there's something that's sort of hardy, sappy? Or is it really like a hard, bright line there?

• 13:36Kelly Weinersmith?

  Yeah, that's a great question. So I'm thinking back at the tree cookies, as they're called, that I've looked at. So this is like you slice through a tree at two different parts and it's sort of shaped in a circle, kind of like a cookie. And I feel like often it looks like there's a pretty clear delineation between what would be the heartwood and what would be the sapwood. The heartwood's like a different color, but it probably does have like layers that are gradations in the process of dying, essentially.

• 14:03Daniel Whiteson?

  Interesting.

• 14:03Kelly Weinersmith?

  Versus cells that are still being fed would be my guess.

• 14:07Daniel Whiteson?

  Right. And so the cambrium is the thing that's making more sapwood on the inside and more bark on the outside. Is that the only part of the tree that's growing? The tree's not like expanding uniformly, sort of like the way the universe expands. It's like only making new rings around the outside.

• 14:22Kelly Weinersmith?

  Yeah, it's only making new rings around the outside. And so say you were to like, put a nail into the side of a tree and you came back 50 years later, that nail would still be at the same height that you had put it. But it would be essentially getting like absorbed by the tree, like layers would have grown around it. And so either that nail wouldn't be visible anymore unless you actually cut into the tree. And as someone who lives out in the woods in an area where there used to be a lot of barbed wire fencing, it's amazing how often we'll cut into a tree and the chainsaw blade will get messed up because it turned out there was a barbed wire like in the middle of the tree and the tree had just grown around it. It was like, nice try, humans. I grow around you.

• 15:06Daniel Whiteson?

  And so if I had like two models of growth in my head, one where like every part of the tree is expanding. So heartwood is always heartwood just becomes bigger. Sounds like you're suggesting a different model where like sapwood becomes heartwood. Is that what's happening here?

• 15:20Kelly Weinersmith?

  Yeah. So sapwood and heartwood are both made out of xylem cells, which are the cells where you get water and the stuff that's dissolved in the water that goes from the ground through the roots and up towards the top of the tree. Both sapwood and heartwood are dead. Those xylem cells are dead. And as those xylem cells get more and more compressed, they become heartwood. So the difference between sapwood and heartwood is that the xylem cells have been compressed so much that water can't move up them anymore. And that happens as you move towards the center of the tree. So sapwood becomes heartwood over time.

• 15:56Daniel Whiteson?

  And then that heartwood basically never changes, right? Because it's dead. Now it's just structural.

• 16:01Kelly Weinersmith?

  So in most trees, that heartwood stays structural and it stays there. And so when you bore through the center of a tree, you can pull out a plug where you can see all of the lines throughout the entire life of the tree. But there are some kinds of trees, like the boa bob in Africa, where the inside is sort of not the same consistency of wood that most of us think of. And it tends to sort of decay and rot away. And so you can't use increment bores for a lot of those trees because the inside is no longer there.

• 16:30Daniel Whiteson?

  But for most trees, basically, the living part of it is like a hollow cylinder. It's more like a tube than like a filled in cylinder. And that's expanding and leaving behind its corpses.

• 16:41Kelly Weinersmith?

  Yeah. Isn't that crazy?

• 16:42Daniel Whiteson?

  That is crazy.

• 16:44Kelly Weinersmith?

  Totally nuts.

• 16:45Daniel Whiteson?

  It's like the opposite of a snake. A snake like sheds its skin, but the living part is on the inside. This is like if the skin was the living part.

• 16:52Kelly Weinersmith?

  Yeah.

• 16:53Daniel Whiteson?

  Wow, trees are weird.

• 16:54Kelly Weinersmith?

  Yes, trees are so weird. Okay. But so why does that growth leave behind rings instead of just like a homogeneous center?

• 17:04Daniel Whiteson?

  Or why is it linked to the year instead of something else, right? What's going on every year that makes this mark inside the tree?

• 17:11Kelly Weinersmith?

  Right. So you get rings in areas where there's clear seasonal differences. And that could be winter, summer, but it could also be wet season and dry season. So not all trees have rings. And in particular, these rings are either like much fainter or maybe even impossible to see in areas where conditions are more homogeneous or more similar all year long. Like a born place like California, probably. But, uh, but anyways.

• 17:35Daniel Whiteson?

  If by boring, you mean consistently wonderful, then yes.

• 17:39Kelly Weinersmith?

  All right, fine. Okay. So at the beginning of a season, the wood is a little bit lighter and it is more aimed at being able to transport nutrients and water up and down during the massive growth that starts at the beginning of the spring. And so that kind of wood is called early wood because apparently these folks are just as clever at naming things as the people who named the rings of Jupiter.

• 18:05Kelly Weinersmith?

  It was a Jupiter or Saturn where the rings are A, B, C.

• 18:09Daniel Whiteson?

  That's definitely Saturn, probably also Jupiter, though I haven't looked that up.

• 18:13Kelly Weinersmith?

  Okay. And then after the early wood, you get, do you want to go ahead and guess, Daniel?

• 18:18Daniel Whiteson?

  I'm gonna guess late wood.

• 18:19Kelly Weinersmith?

  Yeah, yep. You get late wood.

• 18:20Daniel Whiteson?

  Oh, my gosh.

• 18:21Kelly Weinersmith?

  And, and late wood, I think is more about structure. And so it tends to be tighter and closer together.

• 18:26Daniel Whiteson?

  I see. So the kind of new wood that's grown depends on the conditions on the ground. And that changes through the year and that changes the kind of wood that is grown.

• 18:36Kelly Weinersmith?

  Yep. So every year you get this pattern of like light than dark. And those are the rings that you see.

• 18:42Daniel Whiteson?

  And say again, why the late wood is darker than the early wood?

• 18:46Kelly Weinersmith?

  My understanding is that the late wood is meant to be more about structure. So it doesn't need to be so loose so that water can go up to feed the many leaves that are growing at the beginning of the season. When you're at the point where you've got all of your leaves, or maybe even the leaves are starting to come down. The new growth is mostly just about structure. And so it's a different kind of cell that looks a little bit different.

• 19:06Daniel Whiteson?

  Yeah, you make it sound like it's intentional, like the tree got together and it's like, hmm, all right. I think we're ready for some structure.

• 19:13Daniel Whiteson?

  In reality, of course, this is just sort of what has worked, right? And we're reverse engineering it.

• 19:17Kelly Weinersmith?

  Yeah, it also is responding to the environment. And so on very wet years or years with really good growth conditions, the distance between rings is much bigger because the cambrium was able to put in more rows of cells. And so you get a greater distance. Whereas in years where there's droughts or conditions are bad for some other reasons, the distance between the rings are much smaller.

• 19:38Daniel Whiteson?

  And do you always get a ring? Like, what about the year without a summer? Or when there's like a volcanic eruption and we just don't see the sun? Can you trick trees into thinking a year hasn't passed?

• 19:48Kelly Weinersmith?

  So I don't know the answer to that. I have aged fish based on their scales. So I have some knowledge of how the environment impacts aging dynamics. And there are definitely some years where it's very hard to tell the difference between the rings or to tell if there is a ring in a particular place or not. I'm guessing the same thing happens with trees. I would also guess that when you age a tree and you say it's 4,587 years, you really mean like 4,587 plus or minus 30 or something like that.

• 20:18Daniel Whiteson?

  Sure, yeah.

• 20:19Kelly Weinersmith?

  Yeah, but you can use this tool called an increment borer to go through the center of a tree and pull out a tiny little pencil shaped chunk where you can go through and you can age it by counting the rings, but you don't need to kill the tree. It can just handle this little bit of damage. It's like drawing blood from a human or something. And if you get enough of these, you can actually look at climate patterns in a region over time. And so trees give us a little bit of window into the past. One tree doesn't really do it because it could be like one year it was underneath a bigger tree and so it got shaded out, so it didn't grow as much. And then if that tree dies, you know, the next year its growth is bigger. And so there's some other stuff to pay attention to as well.

• 21:03Kelly Weinersmith?

  But we could look at climatic patterns by using these tree rings.

• 21:06Daniel Whiteson?

  Yeah, I remember reading that they use old trees for things like understanding the atmospheric carbon content and all sorts of stuff. It's like an incredible record of what's happened on Earth because it's so sensitive. It's so lucky that it works this way. I mean, I can imagine lots of other ways trees could have evolved that they didn't respond in this cyclical way.

• 21:27Kelly Weinersmith?

  I know. And also for managing fish populations, it's amazing that scales tell you how old they are. We really lucked out that nature works in this way.

• 21:36Daniel Whiteson?

  Nature is a good record keeper, right? There are hints all over the world about what happened on this planet. We just have to be good detectives and like figure out how to read them. And one thing I love about science is all this work that people have done. You know, this like yeoman work to figure out like how we can use some part of nature to reveal secrets of the universe, right? It's not, you don't just sit around and like let the universe download it into your brain. You've got to go out there and do the work and figure out like, oh, we can use this weird rock. And oh, it turns out trees do this weird thing or fish do this weird thing. Like there's so much of experimental science that's people's realizing they could take advantage of a quirk of nature.

• 22:13Kelly Weinersmith?

  Yeah. And then there's so many things you can do with it. It's like, one of the favorite things I came across was that archaeologists are using tree rings to try to date structures. So if you find, for example, a beam in an old house and you assume that it was cut down to build the house, then you can look at other tree cores in the area and sort of match up the fast growth years with the slow growth years. And then you can back date to figure out when that structure was built, even if you don't have that record anywhere. It's so amazing. The more you understand about the world, you get all of these surprising linkages that you can use to learn even more. It's, it's super cool.

• 22:49Daniel Whiteson?

  It's incredible.

• 22:50Kelly Weinersmith?

  Okay. But to get back to carbon 14 dating, it turns out that carbon 14 dating is also a method that we use to date some of the trees that we come across. So we already talked about the baobab, which sometimes rots in the inside. And so you can't use an increment bore to like, get a little sample of the tree to age it because it doesn't really have a center. But you can use carbon 14 dating and pull the innermost wood that you can find to get an estimate for how old the tree is. So these are the various methods that we use to age trees.

• 23:21Daniel Whiteson?

  So like some of the interior records essentially have been destroyed, but you still have a few. And so you can say the tree is at least 1,100 years old, or at least 75 years old, or whatever. But you don't know what you've missing.

• 23:33Kelly Weinersmith?

  Yep. That's exactly right.

• 23:35Daniel Whiteson?

  Yeah. Fascinating. Well, it's incredible to me how long these trees live. And, you know, trees to me are just stunning creatures. You know, like if we didn't have trees, or if I'd never seen a tree, and you described them to me like, hey, there are these things that build themselves out of air over time, drinking sunlight and reproduce themselves and provide oxygen. I'd be like, that's some crazy science fiction nonsense. But they're real.

• 23:57Kelly Weinersmith?

  It's amazing. And they're beautiful. And we can use them to build our homes.

• 24:03Daniel Whiteson?

  All right. Well, I want to hear all about the world record holders for oldest trees in the world. But first, we have to take a quick break.

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• 26:42Speaker 06

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• 26:58Daniel Whiteson?

  Okay, we're back and we're talking about the weird, the amazing, the beautiful, the fantastical, the Californian, the Virginian, the worldwide tree. It's everywhere and it provides us with oxygen and teaches us about the history of our own planet. So Kelly, tell us, where are the oldest trees in the world? And are they in California?

• 27:18Kelly Weinersmith?

  Maybe they're in California. There are a couple other contenders for oldest tree in the world. But at the moment, I think the most widely accepted oldest tree in the world is Methuselah, which we talked about in the intro. Somewhere between 4,500 and 5,000 years old, the coordinates are not public because they don't want people to go and like carve their names into the side of it because humans do stuff like that. Guys.

• 27:42Daniel Whiteson?

  Can we just hold on for a moment? Like back, I'm like, wow, 5,000 years old? What was happening on Earth 5,000 years ago? So this tree is like older than the Great Pyramids?

• 27:52Kelly Weinersmith?

  This tree put down its roots during the age of the pyramids. I think this is the Old Kingdom. Yeah, incredible. So it saw the fall of ancient Egypt, the rise and fall of ancient Rome and ancient Greece, like we said in the intro. So many generations of humans. It's mind boggling. I'm not very eloquent. I can't capture this adequately. It's just incredible.

• 28:15Daniel Whiteson?

  It really just gives you a sense for the tiny blip of time that we exist on this planet. And of course, even that, right? 5,000 years is a tiny blip of time for the planet. That's the thing that these old trees do for me. They give me this like tiniest taste of the deepness of time, the incredible vastness of time in the universe more broadly. And then, of course, here on Earth. So do you think that these trees are going to see, you know, the fall of our current civilization? How long do bristlecone pines live?

• 28:45Kelly Weinersmith?

  So I think the bristlecone pines that are 5,000 years old are not looking young.

• 28:55Kelly Weinersmith?

  But I do think that there are some clonal organisms that we'll talk about later, like those stands of quaking aspens that can live for over 10,000 years. And I hope that we live longer than the quaking aspen stands that are alive today. We as a species, not me personally, but I don't know. We'll have to wait and see. What do you think? Are we in imminent decline, Daniel?

• 29:17Daniel Whiteson?

  That remains to be seen. I was mostly asking about the lifetime of these trees. If you find a population of trees and the oldest ones are about 5,000 years old, that means either they evolved 5,000 years ago and they're going to live a long, long time, or that's roughly as long as they can. Like, have bristlecone pines been living for 5,000-ish years for millions of years? And this is just sort of like how long they typically live? And we're visiting the old folks home for bristlecone pine?

• 29:45Kelly Weinersmith?

  I don't know, and I don't think that most people know. What would you have to know in order to answer that question? I guess you would have to find dead bristlecone pines. You could age when they died and determine that they had been alive for 5,000 years. I suppose in these dry environments, that kind of petrified wood could exist, but I don't know if it does exist.

• 30:09Daniel Whiteson?

  Yeah, well, we can tell when a tree dies, right? Because of carbon 14 dating. And you could count its rings. So in principle, it should be possible to know.

• 30:16Kelly Weinersmith?

  You could count its rings if it didn't like. So most of the trees on my property, eventually they rot away and decay and you can't find them anymore. But if it petrified and you could find it, I don't know the answer, but my guess would be that they have been living for a very long time. But if you go out to a long enough time period, you have to start thinking about things like, well, where were they when the last glacial event happened?

• 30:37Daniel Whiteson?

  Oh, yeah.

• 30:38Kelly Weinersmith?

  And it turns out that bristlecone pines tended to be up in the mountains, high enough and out of the way enough, that they weren't bothered by the last glacial event. But it could be that there are trees out there that would live for a very long time, but they happens to be in habitats where, when the last glacier came through, it knocked them all out because they can't run away like we can. It's one of the downsides of being a tree.

• 31:01Daniel Whiteson?

  Right. That's amazing. These guys live so long, you have to think about the changing conditions of the earth when they were babies or when they were growing up. That's incredible.

• 31:10Kelly Weinersmith?

  It is.

• 31:10Daniel Whiteson?

  All right. So Methuselah is maybe a contender for one of the oldest trees on earth. What else do we find in the old folks' home for trees?

• 31:18Kelly Weinersmith?

  Well, so there was a tree called Prometheus that was also a bristlecone pine, but usually the contenders have to be trees that are still alive. But unfortunately Prometheus was cut down in its 5,000 year prime.

• 31:32Daniel Whiteson?

  Oh no. Was it by some terrible tourist?

• 31:34Kelly Weinersmith?

  No, it was by, I think, a grad student. So I know. Okay. So there was this misconception that old trees were probably the biggest trees. And that makes sense. You know, you look at the redwoods and you're like, oh, you might be so old. But actually, there's this trend where the older trees within a species tend to be the smaller ones that started their lives, growing more slowly, and maybe even over time, didn't get to be as big. They're just sort of like tiny and stodgy, and I love it. And so I think this student didn't realize that they were dealing with what might be the oldest tree on the planet. And so they were trying to get the age. The exact details of the story have been sort of lost to history, but a version of the story is that the student was trying

• 32:17Kelly Weinersmith?

  to get the age using an increment bore. So this thing where you hand crank it into the tree, and that just wasn't working out. And so they actually did get permission from the park service to cut the tree down.

• 32:28Daniel Whiteson?

  Oh, no.

• 32:29Kelly Weinersmith?

  And then when they cut the tree down, it just turned out that it was 5,000 years old.

• 32:34Daniel Whiteson?

  Oh, my God.

• 32:35Kelly Weinersmith?

  Maybe the oldest tree ever.

• 32:36Daniel Whiteson?

  That must have been heartbreaking.

• 32:39Kelly Weinersmith?

  Yes. I think that student did report later that they regretted for the rest of their life that they cut that tree down.

• 32:46Daniel Whiteson?

  Imagine surviving for 5,000 years and then some grad student is like.

• 32:53Kelly Weinersmith?

  Oh, man. Yeah, the glaciers didn't get you, but the grad student did.

• 32:59Daniel Whiteson?

  Academia comes for us all eventually.

• 33:01Kelly Weinersmith?

  Oh, man. Yep, it gets us. So anyway, tragic story. So there's also a tree in Chile, the Alarce tree. And again, sorry, my apologies if I'm mispronouncing it, but there is a tree in Alarce Castero National Park that is 80% likely to be over 5,000 years old. It's estimated to be 5,484 years old. And so that tree could win.

• 33:27Daniel Whiteson?

  Where do you think that 80% uncertainty comes from? Is that from like the rings being fuzzy? Or what we were talking earlier, like not every ring is present or visible?

• 33:36Kelly Weinersmith?

  The rings being fuzzy, I think, is a problem. Another problem is that sometimes where you go through the tree can influence how many rings you see. And so people tend to do the boring, like, you know, to get your sample at about like chest height. But I think if you go down even lower, sometimes you can get some additional rings. It's just complicated. No answer is ever as clear as you want it to be in science.

• 34:01Daniel Whiteson?

  Well, I appreciate that there's uncertainties. You know, I've seen talks in biology where you see like data plotted with no uncertainties and like a line drawn through in it. And you're like, what are we doing here, folks? So I'm always very impressed when I see biology with error bars. So kudos to you.

• 34:18Kelly Weinersmith?

  Hey, man. A lot of us understand error bars and confidence intervals and would never publish a paper without them.

• 34:26Daniel Whiteson?

  I'm so glad to hear it.

• 34:27Kelly Weinersmith?

  All right. Anyway, we had talked about that tree, the African baobab, where the inside sometimes rots out. But with carbon 14 dating and then attempts at aging the trees, using the rings for the trees where that works, we think that they can live to be as old as 2,500 years.

• 34:43Daniel Whiteson?

  Wow.

• 34:44Kelly Weinersmith?

  There's about 25 species of trees that we know of that we think can live to be 1,000 years old or older.

• 34:52Kelly Weinersmith?

  But it's important to note that not all trees live to be super old. Like, right now, it's spring in Virginia, so it's more beautiful here than anywhere else. And the dogwoods are going to be blooming pretty soon. And dogwoods live to be like 20 or 30 years. They can live to be as much as like 80 years, I think. But like, a lot of them only live to be 20 or 30 years. So it's not the case that all trees do outlive humans.

• 35:16Daniel Whiteson?

  Well, what about the famous redwoods? These are old trees also, but they're not in like the top 10 oldest trees. But they must be hundreds of years old, right?

• 35:24Kelly Weinersmith?

  Yeah, so redwoods and giant sequoias are amongst the species of trees that can live to be over 1,000 years old. So they're found amongst those 25-ish species we know of. But I don't know that there are any redwoods that are contenders for the oldest tree.

• 35:43Daniel Whiteson?

  All right, so then why is there such a huge range? Dogwoods live happily for just a couple of decades. Bristlecone pines scratch out a thorny existence for thousands of years. Redwoods become enormous over about a millennium. Why do these things live such an incredible range?

• 36:01Kelly Weinersmith?

  So this is ecology? So what do you think the answer is?

• 36:06Daniel Whiteson?

  We don't know.

• 36:06Kelly Weinersmith?

  Yeah, we don't know. Yeah, both of those work. So the papers that I read, it seems like, so you know, there are those 25 species that I mentioned.

• 36:14Daniel Whiteson?

  Yeah.

• 36:15Kelly Weinersmith?

  In many cases, they are not closely related tree species, or they're not super closely related. And it seems like we have a different answer for a lot of those different species. So for example, part of why we think the bristlecone pines have lived so long is that they manage to eke out an existence in an environment that is very dry and is up at the top of a mountain. And it's just not a nice environment for other competitors or for pests. And when they escape from these competitors and these pests, they can just focus on slow growth and they can live for a really long time because they don't have to worry about these other competitors. But then you get the redwoods in these moist environments with lots of competitors and lots of pests, and they do manage to live for a long time.

• 36:58Kelly Weinersmith?

  And so it seems like you'd need a whole different explanation to. Figure out why redwoods are able to live for so long.

• 37:04Daniel Whiteson?

  It seems to me sort of connected to the question we talked to Katie about, you know, our strategists and case strategists, like from a species point of view, it doesn't really matter if you live a long time. Another totally valid strategy is to just like have a kid every 30 years and then die off and make room for your kids, right? Like they're definitely different strategies from an evolutionary point of view that could work to probably get your species down through history, right?

• 37:28Kelly Weinersmith?

  Yeah, exactly. And additionally, our data set is complicated by things like what we've talked about already, which is, you know, during the last period when the glaciers came through, maybe there were a bunch more species that would have lived for 5,000 years, but they all got wiped out by the glaciers. Another problem is that humans have been cutting down trees for a really long time to build our houses and, you know, to build our skyscrapers, just to build a lot of different stuff. And so we have removed a lot of trees from the landscape. And so what we have left to age is maybe a subset that is less informative than it would have been if all of the trees had still been there. Or every once in a while you get an outbreak or something like the United States used to have tons of chestnuts, like everywhere I looked now there's pines and oaks.

• 38:14Kelly Weinersmith?

  If I had lived here before chestnut like, the most common tree in my area would have been a chestnut. But now we don't have any of them in the area. And so we have a biased subset from which to try to answer these questions. Why do some trees live longer than others?

• 38:28Daniel Whiteson?

  But we always have a biased subset, right? We just have the subset that happened to survive that made it through the death gauntlet of the present conditions. We never know, like on average, over a thousand parallel Earths, what would have survived? We just got the ones that happened to get lucky and happened to survive this time, right? Isn't that always true of evolutionary history?

• 38:49Kelly Weinersmith?

  Yes, I'd say it's also sort of always true with physics too. Like, you know, you only have the information that you've already created tools for. You don't know what you're missing. And so I think in general, a big part of being a scientist should involve being humble about what you do and don't know.

• 39:06Daniel Whiteson?

  No, it's important to always put this in context, right? And remember that we have a tiny fraction of the information and that fraction is biased for sure.

• 39:13Kelly Weinersmith?

  So one thing to note that we talked about earlier is that growing slowly seems to be associated with longer life for trees. And that can either be at the species level or within a species. So it looks like individuals that tend to grow slowly early in life are also the ones that tend to live longer. So if they're growing more slowly, they're investing in a denser, higher quality wood. And maybe they're also investing in stronger roots or some chemicals that can fight off pests. And so this investment in strength helps them when, for example, a hurricane or tornado comes by. Maybe they're likely to be still standing when that's done.

• 39:55Kelly Weinersmith?

  Whereas if an individual grows quickly, then the quality of the wood that they produce is less good. And so something is more likely to take them out if, you know, something like a hurricane or tornado comes through. So individuals who grow more slowly tend to be the ones that live longer.

• 40:11Daniel Whiteson?

  Well, how does this map to long and short lifetimes for other critters? Like in mammals, what's the longest lived mammal?

• 40:17Kelly Weinersmith?

  Yeah, so this idea does map pretty well to the R and K strategy stuff that we were talking about with Katie when she was on the show. You end up with some species that grow fast and some species that grow slow.

• 40:29Daniel Whiteson?

  Okay.

• 40:30Kelly Weinersmith?

  There's also this idea where if you are not growing as fast as the other mammals and you invest in growing really quickly to try to catch up, the quality of that fast grown muscle or fast grown, you know, bones, anything that you grew fast is probably not as good as if you had grown sort of slowly and invested in doing it right. So in multiple flora and fauna, we see the signature of fast growth sometimes coming at the expense of the quality of that growth.

• 40:58Daniel Whiteson?

  I guess I wasn't that interested in mammals in particular, more like animals. Cause I know that, you know, there's some sharks that have lived for hundreds of years and turtles live for hundreds of years, whereas like I know mice live for just a few years, but they're also tiny. So is this like size and age correlation work more broadly?

• 41:15Kelly Weinersmith?

  I don't know. It would be fun to do a whole episode on aging at some point. I know Greenland sharks can live to be like hundreds of years old, but I don't know why we think Greenland sharks in particular live that long. Somebody might know, but I don't know.

• 41:29Daniel Whiteson?

  Somebody's probably gone down and tried to take a core sample of Greenland shark and I bet that didn't go very well.

• 41:33Kelly Weinersmith?

  No, no, they do not look like happy sharks. They look old. You look at them and they've got like sadness in their eyes. Not that all old people are sad. I'm backing up, I'm backing up.

• 41:43Daniel Whiteson?

  Old trees don't look sad. Old trees have a grace and a beauty that's very hard to match.

• 41:48Kelly Weinersmith?

  Oh, my gosh, they do. That is true for so many ancient individuals.

• 41:52Daniel Whiteson?

  Yeah. All right. So let's hold some reverence for the old folks among us and take another break so we can gather our energy and talk about how trees live so long and answer the listeners' question about why they live longer than people.

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• 44:54Daniel Whiteson?

  Okay, we're back and we're talking about how California is beautiful and filled with the oldest, the tallest, the biggest, and probably the most beautiful trees in the world.

• 45:03Kelly Weinersmith?

  Because there's not a lot of competition, because what trees would want to live there if they could live in Virginia?

• 45:09Daniel Whiteson?

  You're saying if you could survey trees and offer them a spot in Shenandoah, they would all pick up and move?

• 45:15Kelly Weinersmith?

  Yeah, I bet. Who wouldn't?

• 45:17Daniel Whiteson?

  You might be right. You might be right. It is beautiful. All right, so tell us, these oldest trees, how is that they go about living so long? What tricks do they have under their bark that let them survive for thousands upon thousands of years?

• 45:31Kelly Weinersmith?

  So, trees are so weird and so unlike anything I've come to expect.

• 45:39Kelly Weinersmith?

  As a mammal, there are things I expect bodies to do. And trees just don't follow any of those rules. Okay, so one, and this is kind of amazing. So we talked about that cambria layer, the layer that is growing the bark while also growing the wood inside of the tree. The cells in that layer don't show evidence of senescence.

• 46:00Daniel Whiteson?

  What's senescence?

• 46:01Kelly Weinersmith?

  So senescence is like getting old and sorry, everybody, but you know, the quality of the cell sort of deteriorating over time.

• 46:10Daniel Whiteson?

  So you're saying in some trees, you can see these cambria layers aging, but in the trees that live a very long time, they just keep going?

• 46:18Kelly Weinersmith?

  I think that you don't see cambria cells aging in like any trees.

• 46:24Daniel Whiteson?

  Oh.

• 46:24Kelly Weinersmith?

  And this is why trees in general, on average, tend to live a long time.

• 46:30Daniel Whiteson?

  Oh, fascinating.

• 46:31Kelly Weinersmith?

  We're still trying to figure out why this happens, but the cells just seem to have this like fountain of youth thing going on. And so because the cells aren't aging, the things that usually kill trees isn't, you know, it just got old and stopped working, but it tends to be things like fire or insects or erosion or hurricanes. It's, you know, things external to the tree that end up being the cause of the tree death.

• 47:00Daniel Whiteson?

  This sort of seems like the tree is constantly replicating itself. Like every few years, you basically have a new tree built around the body of the old tree.

• 47:09Kelly Weinersmith?

  And so I'm going to jump out of place in my outline now because yes, it has this amazing way of replicating itself where for some trees, if it like, for example, falls over, or if some of the branches touch moist soil, the branches or the part of the tree that fell over can start putting down roots and a new sapling comes up from there.

• 47:29Daniel Whiteson?

  What?

• 47:30Kelly Weinersmith?

  Right.

• 47:30Daniel Whiteson?

  That's crazy. It's like if I put my elbow in a bowl of oatmeal and like turned into a person.

• 47:36Kelly Weinersmith?

  Another Daniel. You know, it wouldn't be like it produced one of your kids. It's like producing a clone of you.

• 47:42Daniel Whiteson?

  Ooh.

• 47:42Kelly Weinersmith?

  So like another Daniel emerges from your oatmeal.

• 47:47Kelly Weinersmith?

  I'm glad I didn't give you oatmeal when you were at our place, so.

• 47:51Daniel Whiteson?

  Cause you can't take more than one of me, that's for sure.

• 47:53Kelly Weinersmith?

  No, that's actually a world full of Daniels would have been great, but.

• 47:56Daniel Whiteson?

  Nobody believes you.

• 48:00Daniel Whiteson?

  All right. So these trees have these weird ways of cloning themselves.

• 48:03Kelly Weinersmith?

  Yeah. So they've got these weird ways of cloning themselves and they also have other weird ways of fixing themselves. Throughout the tree, there are these buds and some of the buds will like turn into branches and stems and leaves and stuff like that. But some of those buds stay dormant and while the leaves are growing, a hormonal message is getting sent to those buds. That says, stay put, don't develop, stay a bud. And so it stays a bud and doesn't do anything. But then if something happens and like that branch falls off or something and those leaves are no longer sending the message. That bud snaps into action and starts, you know, building a new stem or something like that.

• 48:45Kelly Weinersmith?

  So trees have all of these different parts that are waiting to emerge. So it would be like if your fingers were sending a message to your wrist saying, we've got enough fingers. Don't worry about it. But then if you lost your fingers, that message is no longer being sent to your wrist. And your wrist is like, time to grow more fingers. And so it's just ready to regenerate what had been lost and it's just kind of like standing in wait.

• 49:07Daniel Whiteson?

  Wow, that's incredible. That's so different from the way our bodies work. It feels so alien.

• 49:12Kelly Weinersmith?

  So alien. Yeah. Okay. And so another thing that's amazing about these trees is, you know, part of them is alive, but a lot of them can be dead.

• 49:23Kelly Weinersmith?

  And so for example, some trees and not all trees, but some trees have this system where essentially the like pipes that provide water to the like top part of the tree, the xylem. Instead of essentially like servicing all of the tree, the pipes service a very particular part of the tree.

• 49:42Daniel Whiteson?

  What?

• 49:42Kelly Weinersmith?

  Yeah. And so like with bristlecone pines, erosion exposes the roots to like dry air and it kills some of the roots. But as long as some of those roots are still in good shape, they can provide water and nutrients to like a branch or a couple of different branches. And so you can end up with like, I don't know, 80% of the tree being dead, but 20% sliver still having leaves, still being able to produce seed and still being alive. And so it's like a very slow process of death, but it still counts as alive because it can still reproduce and it, you know, it's still producing green leaves.

• 50:18Daniel Whiteson?

  I never thought about that, how one root doesn't service the whole tree. It's like this root is for that branch and this root is for that branch. And so if you kill some of the roots, you're killing part of the tree. You're not just weakening the whole tree. That's fascinating. It's like if I had 10 mouths and I need to like feed this one for that leg and this one for the other leg. And like, oops, there wasn't any oatmeal left for my right arm. So that's just going to be hungry today. And that's weird.

• 50:44Kelly Weinersmith?

  There are tree species where like one root has, you know, like multiple, we'll call it pipes that come out of it and it feeds different parts of the tree. But there are some species of tree where you get this more tight link between a certain set of branches and a certain root. And in that way, it's able to sort of die in sections and eke out in existence for longer.

• 51:03Daniel Whiteson?

  It's almost more like a community than an individual, right? They're just like a bunch of branch root systems that are sort of like growing together. And some of them die off and some of them continue. It's like a little community of mini trees.

• 51:13Kelly Weinersmith?

  So I think that comparison works better for our next example. I feel like what we just talked about would be more like, you know, everything but my hand could die, but my hand is still alive and so you'd still call me alive.

• 51:27Daniel Whiteson?

  That sounds like a horror movie I don't want to see.

• 51:29Kelly Weinersmith?

  Yeah, no, me as well. But the final example for how trees manage to live so long is cloning. So you have these trees called quaking aspens in the Rocky Mountains. And they're absolutely gorgeous. They're like, you know, these long white trees. They turn beautiful colors in the fall and their roots are able to put out what's called a ramit. Ramit is a general word for an individual clone when you have like a clonal organism. But it produces a stem will come out from the root and it will turn into a tree. And then that tree will produce more roots and then it will also have a ramit. So a stem that comes out. It's all the same genotype.

• 52:09Kelly Weinersmith?

  They're all connected by their roots and can take up over 100 acres of land. And it's all the same genotype. And so, you know, you can say, okay, well, that doesn't really match how I think of an individual. And so it's cheating to say that you get to count all of that living stuff. But they can live for like 10,000 years, we think. And so, you know, if you're willing to count that as an individual, because it's all the same genotype and has all the same genetic makeup. I'm sure there's some mutations in there, but you know, very similar. Then that can live for up to 10,000 years.

• 52:43Daniel Whiteson?

  Well, that's interesting and really challenges your philosophy of like, what is an individual? I mean, if we had human cloning and you turned 85 and we decided to make a new Kelly, would you consider that Kelly to be the same as you? And then when you died, would you feel like, no, I'm still alive?

• 52:58Kelly Weinersmith?

  I see your point, but like this tree is able to do that with no help. Like it's incredible to me and they're also able to produce seed. So they can produce this way, but they can also produce seeds that can go off and start this whole thing, you know, going somewhere else. I think it's an interesting philosophical debate about whether all of those trees in a hundred acres counts as the same individual or not. But one way or another, it's an amazing evolutionary strategy to replicate an organism's genes and get them spread throughout the environment.

• 53:29Daniel Whiteson?

  I guess it does depend on what you consider to be the individual, because in my case, to feel like I'm still alive, I would want to keep my memories, my personality, all of my experiences. And if I like butt off a new Daniel on my elbow, probably wouldn't have all those experiences. And so it wouldn't really be me, even if it had the same genotype. So there's a whole nature versus nurture aspect. Yeah, fascinating. Wow.

• 53:53Kelly Weinersmith?

  Yeah. So the listener wanted to know, why do humans not live as long as trees? And I think the answer is that trees have just gone down such a different evolutionary path than humans have, that they are able to sort of die incrementally and sort of really stretch the process out. There are a lot of pieces that all need to be working in order for our bodies to keep going, whereas trees are sort of able to do things like compartmentalize to eke out an existence for a lot longer.

• 54:23Daniel Whiteson?

  Yeah. I'm sometimes surprised that I'm living as long as I am when I have all these bits that all have to work all the time. And they all seem sort of complicated. Like we are a very elaborate meat machine. It's amazing that we keep going as long as we do.

• 54:37Kelly Weinersmith?

  I absolutely agree. And it's amazing that we don't encounter even more problems along the way, given how many things have to go perfectly in order for us to continue existing the way we do.

• 54:47Daniel Whiteson?

  Well, one thing that I think humans will continue to do as we age is to be curious about the world and to wonder and to build knowledge. And I'm just glad that human knowledge builds from generation to generation. We can pass this down. You don't have to be 5,000 years old to have 5,000 years' worth of knowledge, because we're able to inherit it from all the folks that were curious before us.

• 55:08Kelly Weinersmith?

  Yes, and it became so clear to me while researching this, just how important that knowledge is and how it builds on each other and how dendrochronology, which is the aging of trees, helps you with archaeology. And it's just, we're very lucky to have all of this cultural ability to transmit knowledge.

• 55:24Daniel Whiteson?

  It is incredible. And I love the depth of nerd-dom that exists in so many little facets of science. People have figured out how this works for trees and helps us in other areas. That requires an individual to be super fascinated by this topic and devote their life to it. And wow, I'm just so grateful that there are people out there who are curious and pushing knowledge forward in every direction simultaneously.

• 55:47Kelly Weinersmith?

  Thank you for being curious and listening to our show, and we hope to see you at the next episode.

• 55:52Daniel Whiteson?

  Tune in next time. Thank you for answering my question. You answered it really well. And it's cool how trees can be alive in some places and dead in other places at the same time.

• 56:10Kelly Weinersmith?

  Daniel and Kelly's Extraordinary Universe is produced by iHeartRadio. We would love to hear from you.

• 56:15Daniel Whiteson?

  We really would. We want to know what questions you have about this extraordinary universe.

• 56:21Kelly Weinersmith?

  We want to know your thoughts on recent shows, suggestions for future shows. If you contact us, we will get back to you.

• 56:28Daniel Whiteson?

  We really mean it. We answer every message. Email us at [email protected].

• 56:35Kelly Weinersmith?

  Or you can find us on social media. We have accounts on X, Instagram, Blue Sky, and on all of those platforms, you can find us at D and K Universe.

• 56:44Daniel Whiteson?

  Don't be shy. Write to us.

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