About this transcript: This is a full AI-generated transcript of How Trees Secretly Shaped The World — BBC Wildlife Documentary from Real Wild, published October 17, 2026. The transcript contains 17,366 words with timestamps and was generated using Whisper AI.
"NINETI MILLION MILES FROM US IS THE POWER THAT SHAPES OUR WORLD, OUR VERY OWN STAR, THE SUN. WE SEE IT SHINE IN THE SKY ABOVE US, BUT BEYOND OUR SIGHT, SOMETHING DRAMATIC IS HAPPENING. THE SUN IS GOING INTO OVERDRIVE. OUR STAR IS MORE ACTIVE NOW THAN IT'S BEEN FOR A DECADE. IT'S SENDING Eruptions..."
[00:00:00] Speaker 1: NINETI MILLION MILES FROM US IS THE POWER THAT SHAPES OUR WORLD, OUR VERY OWN STAR, THE SUN. WE SEE IT SHINE IN THE SKY ABOVE US, BUT BEYOND OUR SIGHT, SOMETHING DRAMATIC IS HAPPENING. THE SUN IS GOING INTO OVERDRIVE. OUR STAR IS MORE ACTIVE NOW THAN IT'S BEEN FOR A DECADE. IT'S SENDING Eruptions OF SUPERHEATED PLASMA AND VAST WAVES OF RADIATION TOWARDS OUR PLANET, WITH THE POTENTIAL TO DISRUPT OUR LIVES IN COMPLETELY UNEXPECTED WAYS. AT THE SAME TIME, A NEW GENERATION OF SATELLITES IS SHOWING US THE SUN IN MORE DETAIL THAN EVER BEFORE. IT'S ALWAYS PULSATING.
[00:01:19] Speaker 2: I'M HELLEN CHERESKY, AND I'M HELLEN CHERESKY. TOGETHER, WE'RE GOING TO UNRAVEL WHAT'S HAPPENING TO OUR SUN. FROM BRITAN'S LEADING CENTER FOR SOLAR RESEARCH, WE'LL USE THE LATEST SATELLITE IMAGES AND TEAM OF WORLD-CLASS EXPERTS TO DECODE THE SUN'S INNER WORKINGS.
[00:01:38] Speaker 3: THERE'S SOMETHING IN THE SUN'S ATMOSPHERE JUST SNAPPED.
[00:01:41] Speaker 1: WE'LL EXPLORE THE SUN'S MOST SPECTACULAR DISPLAYS.
[00:01:45] Speaker 2: I LOVE YOUR LABORATORY, IT'S BRILLIANT. INVESTIGATE ITS MYSTERIOUS CYCLES OF ACTIVITY. SO IT TOOK SECONDS TO GET FROM THE SUN TO THE SATELLITE. SO THAT'S RIGHT.
[00:01:57] Speaker 1: AND DISCOVER HOW OUR SUN IS BEHAVING RIGHT NOW. 70 MILES WEST OF LONDON Lies BRITAN'S ANSWER TO NASSER. THIS IS THE ROTHERFORD APPLETON LABORATORY IN OXFORD SHARE. AT RAL, SATELLITE INSTRUMENTS ARE DESIGNED AND TESTED BEFORE THEY'RE LAUNCHED INTO SPACE. AND SCIENTISTS ARE ANALYSING THE LATEST INFORMATION THESE SATELLITES BEAM DOWN AROUND THE CLOCK. IT'S ONE OF THE MOST IMPORTANT CENTRES OF SOLAR RESEARCH IN THE WORLD.
[00:02:53] Speaker 2: WE'VE SET UP INSIDE ONE OF RAL'S GIANT RESEARCH FACILITIES. SO THAT WE CAN TALK TO SOME OF BRITAN'S LEADING SOLAR SCIENTISTS. AND SEE FOR OURSELVES THE EXTRAORDINARY IMAGES THEY'RE USING TO STUDY OUR STAR.
[00:03:11] Speaker 1: WE CAN'T LOOK DIRECTLY AT THE SUN WITHOUT DAMAGING OUR EYESIGHT. BUT A NEW FLEET OF SATELLITES ARE ALLOWING SCIENTISTS HERE AT RAL FOR THE FIRST TIME TO GET A UNIQUE PICTURE OF THE SUN. IN 2006 NASA LAUNCHED THE TWIN STEREO SPACECRAFT TO OBSERVE THE SUN FROM TWO SIDES SIMULTANEOUSLY. THE SOLAR DYNAMICS OBSERVATORY FOLLOWED FOUR YEARS LATER. IT'S ABLE TO VISUALIZE THE SUN IN HIGH RESOLUTION FOR THE FIRST TIME. THESE SATELLITES SHOW THE SUN AS FAR MORE THAN SIMPLY THE BURNING DISC IN THE SKY THAT WE SEE. HERE AT RAL, HEAD OF SPACE SCIENCE RICHARD HARRISON IS RESPONSIBLE FOR ANALYSING THOSE IMAGES. SO RICHARD, HOW ARE THESE NEW SATELLITES ADVANCING OUR KNOWLEDGE OF THE SUN?
[00:04:17] Speaker 3: WELL, THE WHOLE POINT IS THAT WE NOW HAVE BUILT UP A FLEET OF SPACECRAFT, AN INTERNATIONAL FLEET OF SPACECRAFT THAT ARE REALLY STUDYING THE SUN IN PHENOMENAL DETAIL. WE CAN SEE THE SUN FROM BOTH SIDES. WE CAN SEE A COMPLETE STAR. WE'D NEVER DONE THAT BEFORE.
[00:04:33] Speaker 1: AND THESE SATELLITES CAN DETECT TYPES OF LIGHT FROM THE SUN THAT ARE INVISIBLE TO THE NAKED EYE.
[00:04:40] Speaker 3: THE BRIGHTER REGIONS HERE ARE WHAT WE CALL ACTIVE REGIONS AND THEY'RE REGIONS A BIT LIKE VOLCANOS AND EARTHQUAKES ON THE EARTH, IF YOU LIKE. THE REGIONS WHERE THE SUN IS ACTIVE. AND THERE'S A LOT OF INTERESTING STUFF HAPPENING IN HERE. YOU CAN SEE IT WITH YOUR OWN EYES. IT'S SO COMPLEX. IT'S MOVING ALL THE TIME LIKE A PLATE OF WRITING SPAGHETTI.
[00:04:56] Speaker 4: AND, I MEAN, THIS IS AN EXTRAORDINARY IMAGE.
[00:04:59] Speaker 3: WE CAN SEE SEVERAL COLORS PUT TOGETHER, SHOWING YOU THE FULL COMPLEXITY IN ALL OF ITS GLORY, IF YOU LIKE. THE TRULY COMPLEX ATMOSPHERE WRITING IN FRONT OF YOUR EYES. AND, REALLY, THIS SORT OF ILLUSTRATES IT. IT SORT OF PUTS IT IN A NUTSHELL HOW FANTASTIC IT IS TO BE STUDYING THE SUN AS IT APPROACHES A PEAK IN ACTIVITY WITH THIS WONDERFUL FLEET OF SPACECRAFT.
[00:05:20] Speaker 1: THIS PEAK IN ACTIVITY IS KNOWN AS A SOLAR MAXIMUM. IT'S THE HIGH POINT IN A CYCLE THE SUN GOES THROUGH ON AVERAGE EVERY 11 YEARS. FROM RELATIVE CALM TO INTENSE ACTIVITY AND BACK AGAIN. A CYCLE THAT'S FUNDAMENTAL TO HOW THE SUN WORKS. UNDERSTANDING THIS SOLAR CYCLE WILL HELP US DISCOVER THE SECRET LIFE OF THE SUN. BUT FOR MOST OF US ON EARTH, THE SUN IS SOMETHING WE RARELY EXAMINE IN ANY SORT OF DETAIL. TO BEGIN TO UNDERSTAND ITS EXTRAORDINARY POWER AND ITS CHANGING CYCLES OF ACTIVITY, WE NEED THE HELP OF ONE OF THE MOST DRAMATIC EVENTS IN THE ASTRONOMICAL CALENDAR: A TOTAL SOLAR Eclipse. AND TO SEE THAT, I HAD TO TRAVEL TO THE OTHER SIDE OF THE WORLD. NOVEMBER 2012, I'VE COME TO CERNS, AUSTRALIA. I'M JOINING PEOPLE FROM ACROSS THE GLOBE BECAUSE IN 48 HOURS THERE'S GOING TO BE A TOTAL Eclipse. BUT THIS ONE IS SPECIAL BECAUSE IT PROMISES TO REVEAL SOMETHING CRUCIAL ABOUT OUR SUN.
[00:06:50] Speaker 4: Cairns is a relatively small town in Australian terms, it's home to about 130,000 people,
[00:06:56] Speaker 1: but that number could swell by as much as 50,000 in the next couple of days, and all for an event that's going to last just two minutes and two seconds.
[00:07:10] Speaker 5: It's an emotional experience, it's a lovely way to sort of see the world, everyone's happy, it's fantastic, it's a natural spectacle of science.
[00:07:18] Speaker 6: I'm getting excited, yeah. I've never seen a total eclipse before and we've got our glasses and we're all set to go. We've got our fingers crossed for clear skies.
[00:07:28] Speaker 1: You can't safely view an eclipse unless you have glasses with powerful filters.
[00:07:33] Speaker 4: Hi. Hello. That's what I'm after.
[00:07:35] Speaker 3: Very last pair. No way. I was lucky. Three dollars.
[00:07:38] Speaker 4: Did you want some as well? Oh yeah, we've been searching everywhere.
[00:07:41] Speaker 3: Oh, I'm really... This is the very last pair of cans.
[00:07:44] Speaker 4: Sorry. Are you joking? Don't film this. This is horrible. There we go. This is like breaking my heart.
[00:07:50] Speaker ?: Thank you very much.
[00:07:50] Speaker 4: Thank you very much. Thanks a lot. No! It's once every 50 years or so, so make the most of it.
[00:07:55] Speaker 5: Thank you very much.
[00:07:56] Speaker 4: Thanks. Bye.
[00:07:59] Speaker 1: To get an eclipse, the moon must drift between the sun and us. At what's called first contact, the moon begins to block it. But what's extraordinary is what happens when the sun is completely covered. That moment of totality reveals something that's normally hidden by the sun's glare. The sun's faint atmosphere. The corona. And it's the corona that's key to what this eclipse can tell us. The corona is due to reveal itself at precisely 6:38 in the morning, the day after tomorrow. But the fact that we get total eclipses in the first place is thanks to an astonishing coincidence. Earth is the only planet in the solar system from where you can witness a total eclipse. And the reason for that is down to pure luck. The moon is 400 times smaller than the sun, but it's also 400 times closer to the earth. So when the moon's orbit brings it between the earth and the sun, it appears to be exactly the same size as the sun, and it's able to block out its entire surface from our view. There's a total eclipse on average every 18 months, so they're not exactly rare. But catching one isn't easy. The narrow shadow paths they trace on the earth's surface are far more likely to pass over uninhabited regions such as the oceans than a populated area like Cairns. And the timing of this eclipse is significant. Right now, we're due to be at solar maximum, the period of greatest activity in the sun's cycle. But each maximum is slightly different, so scientists need to confirm that we've actually reached it. One way to do that is to study the sun's corona during totality. Click on that.
[00:10:35] Speaker ?: Click on that.
[00:10:35] Speaker 1: And that's what makes this eclipse especially exciting. Delivery. Jay, I think we've got the box you wanted. Even to the most hardened eclipse chasers. Astronomer Francisco Diego has seen 17 total eclipses. This time, he's advising a group of 100 British eclipse chasers. But he's also brought his own equipment.
[00:11:05] Speaker 7: The sun, as far as it is, it's a very...
[00:11:07] Speaker 4: You are the most high-tech scientist I know.
[00:11:09] Speaker 7: This is an ideal container for a very delicate part of equipment.
[00:11:13] Speaker 1: You're like a blue peter scientist. It's brilliant. Can you hold this for me? I can hold that. Careful with the wind. I've got it. Yep. A camera and some homemade filters are all he needs to take detailed photographs of the corona.
[00:11:25] Speaker 7: So what I do, I remove the lens gap here.
[00:11:29] Speaker 1: And it's the shape of the corona in his photos that will tell Francisco if we're at solar maximum.
[00:11:36] Speaker 7: So the eclipse gives that opportunity to admire and to study the outer layers of the solar atmosphere. These layers, the chromosphere and the corona, are an indication of the solar activity. The shape of the solar corona is changing all the time. For example, when the corona is very round, that means the solar activity is at a maximum.
[00:11:57] Speaker 1: Francisco will have only two minutes in which to get a successful picture of the corona. But that brief window of opportunity is threatened by a more familiar force of nature. The eclipse is tomorrow morning and the forecast is not looking good. This is tropical Australia. We're going into the rainy season and the weather could obliterate the whole thing. 2am, the day of the eclipse. I'm following Francisco and his eclipse chasers inland from Cairns to get away from the rain clouds. We have to reach clear skies before dawn or we'll miss the eclipse.
[00:13:06] Speaker 4: We've pulled off the road finally.
[00:13:10] Speaker 1: It's ten past five. And the sky is lightning dramatically quickly.
[00:13:20] Speaker 4: Sunrise is going to be in about half an hour. And first contact... Follow me quick. OK, OK. And first contact is ten minutes after that. The sun has just made an appearance above the clouds. And it's got a chunk out of the top left corner.
[00:13:56] Speaker 1: The moon has begun to block the sun, but the sun is so bright that we won't notice any darkening of the daylight until it's almost completely covered. What do you think, Francisco? It's looking quite skinny now.
[00:14:11] Speaker 7: It's quite skinny. Yes, about ten minutes before totality. So this is where things are going to happen faster and faster. The darkness is going to really come much quicker.
[00:14:22] Speaker 8: You feel it. It's physical. And it's sort of terrifying, actually. Isn't it? It is. I mean, it just... Look at it. It's just... Every moment you can feel the light just dropping and dropping. It's like somebody's stealing the sun. And it's now just a tiny... hair's breadth in the sky. Yeah, we've got two minutes.
[00:14:47] Speaker 7: Two minutes to go. Two minutes.
[00:14:48] Speaker 1: And it's so cold. It's... The temperature's just completely dropped. It's like everyone's collectively holding their breath.
[00:15:10] Speaker 9: Oh, my goodness! Oh, my goodness! Woo-hoo! It's the most amazing thing. I can't believe how beautiful it is.
[00:15:25] Speaker 1: The moon has completely blocked the disk of the sun. A delicate halo is all that remains. It's the corona. Francisco now has two minutes and two seconds to get the photos he needs. It's ridiculous. Here it comes.
[00:15:57] Speaker 9: It's ridiculous!
[00:15:59] Speaker 7: Isn't that amazing? Amazing.
[00:16:04] Speaker 4: It's worth getting up at two o'clock in the morning. Absolutely. Absolutely worth getting up at two o'clock in the morning.
[00:16:20] Speaker 1: I challenge anyone to watch a total eclipse without being deeply moved. It's a glimpse into the hidden workings of the sun.
[00:16:35] Speaker 4: Makes you kind of look at it in a slightly different way afterwards, doesn't it?
[00:16:38] Speaker 7: Absolutely, yes.
[00:16:40] Speaker 4: Somehow you can't take it for granted anymore.
[00:16:43] Speaker 7: No, you cannot. And then, well, life on Earth depends on that. It has been for billions of years, really.
[00:16:51] Speaker 1: That was the first time I've ever seen a total eclipse. But what has the corona revealed? Has the sun reached solar maximum, its peak of activity?
[00:17:09] Speaker 2: Back at RAL, we can now get the answer from Francisco's photographs. An eclipse is a fabulous thing to experience. But there was a scientific reason for taking those photographs. So are we at solar maximum?
[00:17:22] Speaker 7: It looks like we are. We have pictures taken in solar minimum. For example, this one that I was taking in 1994, two cycles ago, when the solar activity was at the minimum. Can you see an axis here?
[00:17:34] Speaker 2: Really clear.
[00:17:35] Speaker 7: Yeah, the sun is very orderly, very steady, very quiet.
[00:17:38] Speaker 2: It's a very clear pattern.
[00:17:40] Speaker 7: By contrast, last year in Australia, we saw the corona in a completely different way. This is the picture we took there. Now, tell me, where is the axis?
[00:17:48] Speaker 2: It's just the same all the way around, isn't it?
[00:17:50] Speaker 7: It's all over the place. It is all over the place. Because the solar activity is blowing the corona in all directions. The sun is extremely dynamic here.
[00:17:57] Speaker 2: So this is an interesting time to study the sun.
[00:17:59] Speaker 7: Very, very interesting. We are very excited about solar maximum. And then again, the sun, in the next years, we'll come down to a quiet stage. And then this whole cycle repeats every 11 years.
[00:18:13] Speaker 2: So what causes these solar cycles? To understand, we first need to know what's going on deep inside the sun. It's a place we can never go. But we can learn a lot from something that makes the journey all the way from the core of the sun to us here on Earth. Sunlight. Sunlight, the light from the sun. We take it completely for granted. But it's still mysterious. Where did it come from? How did it get here? We think of sunlight as simply coming from the sun's surface. But its journey begins deep within our star. And what makes sunlight's journey so epic is the sheer size of the sun. The mass of the sun is two followed by 27 zeros. That is the mass of the sun in tons. And so that makes up 99.85% of the entire solar system. The solar system is basically just sun with a few little fragments circling around the outside. And it's the sun's enormous mass that creates the conditions to produce sunlight. Its intense gravitational pull forces the sun into layers, each with its own special properties. Beneath the thin outer peel is a 200,000 kilometer thick layer where hot material rises and falls. The layer underneath carries the sun's heat outwards. And around 550,000 kilometers down is the core, a 16 million degree furnace. Here, the entire mass of the sun is pushing inwards, exerting vast pressure. And this is where sunlight is born. To understand how that vast pressure creates sunlight, I've come to the National Ignition Facility, NIF in California. Sunlight exists because of a process going on deep in the core of the sun called fusion. And what's happening there is that the pressures and temperatures right in the middle of the sun are so enormous that hydrogen atoms can fuse together. And when that happens, a tiny, tiny bit of mass is converted into a huge amount of energy. And that little process is the key to a star like our sun. Without that single process, the sun would be a cold, dead star and the earth would be a cold, dead planet. So the key to the behavior of the sun and to life on earth is fusion. I'm about to see how the scientists at NIF are trying to make a tiny sun and recreate fusion.
[00:21:39] Speaker 10: All of this is about getting ignition that could change the world.
[00:21:44] Speaker 2: Here, in this dust-free environment, Beth Zanitis creates hydrogen fuel capsules smaller than a grain of rice and destined for a very violent fate.
[00:21:57] Speaker 10: This is called a capsule-filled tube assembly. It's a two-millimeter diameter plastic capsule. 192 laser beams converge on the capsule. And that plastic material blows away from the capsule when it gets hot and under high pressure. And that causes a subsequent reaction of the fuel layer to be compressed so that the hydrogen atoms fuse.
[00:22:22] Speaker 2: To get those atoms to fuse, they need to generate similar pressures to those at the sun's core. 340 billion times the pressure on earth. It's a tall order, but there is a way. The 192 individual laser beams they use are each more powerful than any other laser on the planet. And they all fire at a spherical chamber at the heart of the complex. This is the target chamber. And when the lasers hit the fuel capsule at its center, they bring the atoms together with the same force as in the sun's core. But to truly mimic our star, the NIF team needs to pull off an even greater trick.
[00:23:16] Speaker 11: Proceeding to system shot countdown state.
[00:23:21] Speaker 2: Once ignited, the fusion reaction must keep itself going.
[00:23:31] Speaker 11: Starting system shot sequence on my mark. Three, two, one, mark.
[00:23:40] Speaker 5: May I have your attention? Reparations for shot operations in Laser Bay 2 are underway. Leave Laser Bay 2 now.
[00:23:50] Speaker 2: It's not without its dangers. Before every shot, the area is evacuated. Steel and concrete doors a meter thick enclose the target chamber. A misfire from the most powerful laser in the world could cause a catastrophic explosion.
[00:24:07] Speaker 11: MOR ready for a system shot countdown clock.
[00:24:11] Speaker 2: And even the smallest fusion reaction unleashes a lethal blast of neutrons and high-energy light.
[00:24:17] Speaker 11: Three, two, one.
[00:24:26] Speaker 2: The only visible sign is this flash from the world's biggest laser as it fires. But inside that fuel capsule, they're hoping to create a tiny sun. And with it, man-made sunlight. Another day, another shot. The NIF team routinely achieve short-lived fusion. But today, still no self-sustaining fusion. Yet if we could achieve it on Earth, we'd have the sun's energy on tap.
[00:25:12] Speaker 11: Recreating a small sun in this target chamber that's not too far away is always daunting in a lot of respects. We will get there eventually.
[00:25:26] Speaker 2: It's that elusive trick of generating endless energy that makes our sun so miraculous. The result is the birth of sunlight in the sun's core in particles of light energy known as photons. But their journey is far from over. Imagine this pinball is a newly created photon. That light must now reach the sun's surface. And that is a really complex and difficult journey. Because in between the core of the sun and the surface, there is a seething mass of stuff that we call plasma. Like my pinball dodging the flippers and bumpers, the photon now has to navigate through that plasma. But my pinball, or photon, can't take a direct route out. It's forever colliding with particles of plasma moving at thousands of miles an hour. And with hundreds of thousands of miles of plasma to cross between the sun's core and its surface, a journey that should take two and a half seconds at the speed of light takes much, much longer. Even though it's travelling at the speed of light, as fast as anything can go, it's still estimated that it'll take 10,000 to a million years just to get from the core of the sun to its surface. What we think of as sunlight's journey, the 90 million miles from the sun to the earth, is only the last eight minutes of an odyssey that could have taken thousands and thousands of years. It's lovely, fantastic to think that this gentle light that's touching me now, started off in a violent, dramatic beginning right in the centre of a star, and then spent 100,000 years finding its way out of that star, and finally spent just eight minutes travelling as fast as anything in the universe can travel, the speed of light, to get to me here. But this extraordinary journey raises a question. Fusion in the core never stops. So why does the sun's activity go up and down with the 11-year solar cycle?
[00:28:36] Speaker 1: Back at RAL, that's one of the questions that interests solar scientists. The key lies in how the fusion reaction affects the sun's plasma, that seething mass between the core and the surface. To explain why this leads to solar cycles, we've been joined at RAL by solar physicist Lucy Green.
[00:29:01] Speaker 12: The heat generated by this reaction inside the sun, it heats up the gas. In fact, it super heats it. So the gases, the particles of the gas are torn apart to form plasma. Just as the hot air in the room around us is rising in packets, so the gases in the outer layers of the sun do the same thing. This is called convection. So gases get heated from below and they rise up to the surface of the sun.
[00:29:26] Speaker 1: But because this gas, the plasma, is so hot, it's also electrically charged. So as it moves up and down with the convection currents, it creates powerful magnetic fields. You start to see the magnetic field lines being wound up and eventually it becomes so strong magnetic fields rise up and penetrate the surface of the sun and that's when we have the build-up to solar maximum.
[00:29:56] Speaker 12: At times of solar maximum, those magnetic loops break out from the surface of the sun, drawing the sun's plasma with them.
[00:30:13] Speaker 1: This one loop is many times bigger than the earth, but the sun doesn't stay like that.
[00:30:28] Speaker 12: Eventually the magnetic fields disperse and they rearrange themselves and we go back to solar minimum again where you have the nice ordering of the magnetic field.
[00:30:37] Speaker 1: It does this every 11 years and though the sun may be 90 million miles away, this cycle matters to us here on earth. What is the implication of times of solar maximum for us on earth? What do we experience?
[00:30:55] Speaker 12: Well, the sun is constantly expanding out into space. Its outer atmosphere with the magnetic field is being drawn out into something that we call the solar wind. Yeah. Now at times of solar minimum, the wind is fairly ungusty, it flows quite slow. Quite light. Quite light, but at solar maximum, the magnetic fields start to get more complex and that leads to vast streams of solar wind coming our way.
[00:31:23] Speaker 1: The solar wind is a constant stream of particles flowing out from the sun. It bombards the earth. Most of it is deflected by our planet's own magnetic field. But a small amount of its energy does get through with extraordinary effects. Effects I'd always wanted to see for myself. If you want to see this evidence on earth of solar winds, you need to head right up into areas that are cold, rather sunless and rather dark. This is Lapland in Arctic Sweden. It's February. It's minus 19, and a long winter's night is about to fall. I'm here to see an old friend. She's an extraordinary woman who 15 years ago left her home in Birmingham and came to live here permanently. And all because she became bewitched by the strange and astonishing phenomenon that I'm hoping to witness too. It's called the Aurora Borealis, also known as the Northern Lights. The Aurora is the solar wind made visible on Earth. As the wind encounters our planet's own magnetic field, it sends energy down the magnetic field lines towards the poles, causing our atmosphere to luminesce in ghostly colours. Right now, at solar maximum, is the best time to see the aurora. But I still need a cloud-free, moonless night. My friend Patricia Cowan knows the challenges. She's photographed the aurora countless times.
[00:33:45] Speaker 13: Wow, so that's above here, isn't it? It is above the house, yes. That's one of the early ones that I took when I very first started Northern Lights photography. Oh, my goodness, look at that. This is where we're sitting now.
[00:33:57] Speaker 1: Really? Yeah. You see, I just think I'm going to pop with excitement if I see a sky that looks like that. When we go out this evening, am I going to get to see them? Hopefully.
[00:34:08] Speaker ?: Hopefully.
[00:34:10] Speaker 13: If we can get rid of the clouds. Yeah. We have the darkness. Yeah. We actually do have activity at this moment. Right. So what we need is for these clouds to go away. OK, well, I'm going to get outside and start blowing. And start blowing. Yes.
[00:34:32] Speaker 1: Near the poles, there's a ring-shaped zone where our atmosphere is most affected by the solar wind's energy. Lapland is slap bang in that zone, which is why it's such a hot spot for the aurora. My first attempt to see it. To the naked eye, it's very faint. But with time-lapse cameras, we can see there's definitely aurora going on up there. But although there's no moon to spoil it, there are clouds in the way. Well, it's coming up to 11 o'clock at night. And the cloud is still stubbornly hanging around. There's a few breaks in it. I've had sort of tantalising glimpses of wisps of green smoke across the sky, but nothing like the scale that we know that they're capable of. I have one more night before the moon returns and wrecks my chance of getting a clear view. But it's not just sightseers like me who are drawn here.
[00:35:50] Speaker 4: It's a perfect backdrop for scientists like Gabriela Stenberg.
[00:35:58] Speaker 1: She's interested in an important question. How well is our magnetic field holding up to the constant battering of the solar wind?
[00:36:10] Speaker 14: Let's use this nice snowball to illustrate that. It's a beautiful sun, beautiful sun over here, so from the sun now comes solar wind. Yeah. And at some point it encounters the magnetic field of the earth. Most of the solar wind now goes around like this.
[00:36:32] Speaker 1: How powerful is this solar wind? I mean, obviously we can't feel it because of all these layers of protection, but is it gale force? Is it like a hurricane?
[00:36:44] Speaker 14: What happens is it comes particles and they come very quickly. Yeah. So they move with a speed of like 400 kilometres per second. Wow. So they move really, really fast. So you get this gigantic shockwave where the solar wind slows down. This boundary separating us or our space from the solar wind is very, very, very thin. It's like a thin, almost transparent veil separating us from this blowing wind from the solar wind. And that we think is really cool. How can these really thin boundaries, how are they formed and why are they so thin?
[00:37:30] Speaker 1: So the aurora is but a faint trace of the solar wind's true strength. Out there is a violent collision where it meets our magnetic field. That thin shell gives us vital shelter. Last night in Sweden, it's tonight or never. It's about minus 30 outside and it's absolutely clear. It's been clear all day, so we're going to go out and see what's happening.
[00:38:14] Speaker 9: Oh my goodness, look at those stars. It's so clear. Oh my goodness, look at that. Look what's happening in the sky.
[00:38:31] Speaker 1: With ordinary cameras, you can see it faintly. But it's with the time lapse cameras that we can capture the full glory.
[00:38:44] Speaker 4: Look at that, it's just spanning the whole of the eastern sky like a giant sort of green rainbow.
[00:39:01] Speaker 1: Under this balaclava, I am grinning like the Cheshire Cat. It's mesmerising, isn't it? You can't kind of take your eyes away from it. The aurora is a stunningly beautiful display of the solar wind. But also a reminder of its enormous power. And the protection we get from the Earth's thin magnetic shield. So what would happen if we were ever exposed to the full force of the sun? It's a question that the scientists back here at RAL have been studying intently. The solar wind is a mere hint of the vast amount of radiation and particles that the sun sends our way. It's known as solar weather and its impact on Earth can have a more alarming side. Richard Harrison, head of space science at RAL, is an expert on its most violent form, solar storms. So Richard, we know that the Earth is protected from the full force of solar weather by the Earth's magnetic field. But is there any danger that that magnetic field could be breached?
[00:40:20] Speaker 3: Well, the best way to answer that is actually to look back at the sun's atmosphere again. And these wonderful magnetic loops in the sun's atmosphere. Like elastic bands sort of writhing around, being tied up in knots. And you might expect occasionally something might break. So in these regions you see here, that happens. This image here is actually from helium in the sun's atmosphere. And you see a huge cloud erupting there. That's a billion tons of mass from the sun being ejected into space. So something in the sun's atmosphere just snapped.
[00:40:55] Speaker 1: These gigantic solar storms are called coronal mass ejections. They're the most high energy events in the solar system. And the sun unleashes more of them at solar maximum than at any other time. They can hurl clouds of plasma towards us at alarming speeds. To cover the 90 million miles from the sun, seen here reduced in scale on the right, to the Earth on the left, can take less than a day. And as Helen found out, they have the power to overwhelm the Earth's defences.
[00:41:38] Speaker ?: And they have the power to overwhelm the Earth's defences.
[00:41:47] Speaker 2: Solar storms can destroy satellites. Silence communications. Ground aircraft. But the link they threaten most in our modern lives is our dependence on electricity. If you have any doubt, take a look at this booklet. It's published by Lloyds of London, who are insurers, and they wrote it with the Rutherford Appleton Laboratory. And I think one of the most interesting sections is where it lists the potential impacts that disruption to the power supply would have. And this is important because our power grid is one of the things that's most vulnerable to a big solar storm. The highly charged particles of coronal mass ejections can induce powerful electrical currents on the Earth's surface. overloading circuits and melting transformers. And the reason it matters so much is that everything is interconnected. And so if we lost power, we'd not only lose lighting and heating and the ability to cook our food, we also, for example, lose our fuel because pumping stations rely on having electricity to pump the fuel out of their reservoirs, sanitation, water supplies, communication systems. We know we're vulnerable because we've been hit in the past. In Quebec, the entire power grid went down after a solar storm in 1989, plunging millions into freezing darkness. But we're not helpless. There are precautions we can take against the effects of solar weather. We're already building systems and technologies that are resilient. But it would be even better if we could prepare for specific storms. But for that, we need to know when they're going to arrive. We need an early warning system. Unfortunately, there's one in this building right here.
[00:44:09] Speaker 5: The forecast now trending downward. There were several filaments that erupted or disappeared.
[00:44:17] Speaker 2: The Space Weather Prediction Center in Colorado is the only team on the planet solely dedicated to watching for solar storms.
[00:44:26] Speaker 5: In the next three days, no alerts or warnings are currently issued.
[00:44:30] Speaker 2: The aim is to alert governments, power companies and the aviation and space industries that a storm is on its way. Even a few hours warning can help them prepare. Chief Forecaster Bob Rutledge is going to teach me how to predict solar storms.
[00:44:48] Speaker 15: Space weather really starts with sunspots. What that sunspot is doing, how much is it changing, and how complex are those magnetic fields underneath those spots. Are really what we use to say how likely are we to have significant activity.
[00:45:01] Speaker 2: What are the different events that could happen?
[00:45:04] Speaker 15: When we get a solar flare, that's the start of the event. That's the giant explosion. We see that in this image, like in X-rays. So it's a brightening in light and radio waves. So that's our first clue. The last piece is, does the portion of the sun's outer atmosphere that sits above that, you know, a billion tons of plasma, does it get blown into space as well? So we start to watch, you know, other images of the sun. Like this, for example, where we've blocked out the sun and we watch for the faint pieces of that atmosphere being blown into space. So the ones that go off to the side, albeit beautiful, don't really matter to Earth.
[00:45:40] Speaker 16: Right.
[00:45:40] Speaker 15: It's really looking and seeing, is it coming our way or not? And if so, how fast? And when do we expect it to get here?
[00:45:51] Speaker 2: These images are coming from the same new generation of satellites used by the scientists at RAL. They're our eyes in space that keep watch over the sun. I can see it with visible light. Magnetic fields. X-rays. On a typical day near solar maximum, the sun will send out three coronal mass ejections. Fortunately, today there haven't been any. But dramatic events can happen with little warning. You've got a video here of a very special event.
[00:46:40] Speaker 15: I've picked out from late October 2003 of really, probably the last significant, really big round of space weather activity that we had. We've blocked out the sun so we can see the atmosphere. You'll see the eruption. And then look at that massive cloud. Really symmetrical. It looks like a halo coming straight at you. It was going at tremendous speed. So it made it here in just under a day. So we have the levels one through five, just like a hurricane or tornado. And it was pegged at that five level storm.
[00:47:06] Speaker 2: It was as big as it gets. That solar storm took out the power grid in the Swedish city of Malmo. Tens of thousands were left without electricity. On that occasion, the earth was only struck a glancing blow. But we can't be sure that next time we'll be so lucky.
[00:47:31] Speaker 15: Today, if we saw this happen again, we'd be able to give our partners in the key industries, like the electric power industry, a heads up to say, hey, prepare your systems, and keep them as safe as you can.
[00:47:51] Speaker 2: We're only just beginning to understand solar weather. But we can't afford to ignore it. I've been looking at the sun all day. And yet I haven't actually seen very much sunlight. And now it's got dark. Here's what gets me about today. Imagine the big weather events we have on earth. You know, thunderstorms and even bigger than that, hurricanes. And then take a step back. And all those massive events suddenly become tiny specks on the earth, sailing through this solar weather, which is even bigger. We've come a long way from the idea of the sun as simply a giver of light and warmth. It's effects on our planet are far more complex.
[00:48:44] Speaker 1: Thanks to solar scientists, our sun is being revealed as a dynamic, vigorous fusion reactor, pulsing through its 11-year cycle and belching plumes of highly charged particles in our direction. As the scientists at RAL have shown us, that 11-year solar cycle has become the heart of how we understand the sun. Many of the more surprising effects the sun has on our lives depend on how its activity rises and falls through the cycle.
[00:49:18] Speaker 2: But scientists are now beginning to explore a radically new idea. That these cycles are not as set as we once thought. The latest research suggests that the cycles themselves could be changing. We could be living through bigger shifts in the sun's behaviour than we thought. The clue comes from a phenomenon that astronomers have been observing for centuries. Sunspots. They've been known about since long before the era of satellites or even telescopes. Looking directly at the sun without proper filters is clearly a terrible idea, because you could really, really damage your eyes. But that didn't stop early astronomers from trying. And just sometimes, maybe at sunrise or sunset or on a cloudy day, they'd see something that made the sun worth looking at – tiny dark spots. And for years they just assumed that those spots were planets that were passing between the earth and the sun. And then the telescope was invented and Galileo could draw diagrams like these and map out where these dark spots were. And it became apparent that they're actually part of the surface of the sun. Thanks to those early astronomers, sunspots are one of the few bits of evidence we have about the sun's long-term behaviour. And new research is revealing something surprising about them. The key is how they're created. Sunspots are caused by the magnetic fields deep inside the sun. And we can't see those magnetic fields directly. But the sunspots are offering us some clues as to what's going on. And we know that the more active the sun is, the more sunspots there are. As the sun approaches solar maximum and the magnetic field lines beneath its surface become tangled, the flow of plasma within is disrupted. Hot material from the interior can't rise to the surface. The result is zones of cooler plasma – sunspots. They're like windows in the sun's surface through which we can study what's happening inside the sun itself. The McMath solar telescope in Arizona is the largest in the world. 17 years ago, a study of sunspots began here, led by a group of astronomers, including Matt Penn. They began to look at the average strength of the magnetic fields in the sunspots. Something no one had tried before. So what got you started on this study?
[00:52:42] Speaker 17: So we wanted to take regular observations of the sun to find out what sunspots were doing over time. We know that the number of sunspots increases and decreases in the solar cycle. Actually, that's how the solar cycle was discovered, by early observations of sunspots. During solar minimum, there'd be zero or five sunspots on the disk. During maximum, there could be a hundred. So during that 11-year period, we were wondering what was happening to the magnetic field in sunspots. Was it increasing along with the number of sunspots? Was it flat or was it doing something else? We just didn't know.
[00:53:12] Speaker 2: And is it what you'd expect?
[00:53:14] Speaker 17: Well, no. It turns out that the data showed us something completely different.
[00:53:21] Speaker 2: Matt and colleagues are using an ingenious way of measuring the strength of the magnetic fields and sunspots. A change in the infrared light coming from them. So this is a really lovely, simple method because you can point your telescope at any point on the sun and just from the light coming out of it, this simple thing of watching how these spectral shapes change. You can see exactly how strong the magnetic field is anywhere on the face of the sun.
[00:53:48] Speaker 17: Exactly. So what we're doing is measuring the magnetic field with the spectral line and we've done a survey of about 3,000 sunspots over the past 10 years, measuring the magnetic field strength in each sunspot.
[00:54:00] Speaker 2: And what they've discovered is surprising. Instead of rising and falling in line with the solar cycle as expected, the magnetic strength of sunspots has been steadily decreasing year by year. Right back in 2000, the magnetic field is quite high and it's just gradually gone down and down and down over the past 10 years, really quite consistently.
[00:54:24] Speaker 17: So a decreasing trend means that in the future, we may not have any sunspots at all.
[00:54:28] Speaker 2: It's an extraordinary result. The trends suggest that over and above the familiar 11-year solar cycle, there are bigger patterns in the sun's activity. And in the long term, we may be heading for an extended quiet period, what solar scientists call a grand minimum. Intriguingly, we've been here before. Thanks to those historical records, we know that around 350 years ago, sunspots almost vanished for 70 years. So it looks as though the sunspots could be dying away. If that happens, what difference does it make to us?
[00:55:20] Speaker 17: Right. If sunspots do go away and we enter a new grand minimum, there are possible effects on the climate. But records suggest that the temperature in Europe, for instance, decreased during the last grand minimum.
[00:55:36] Speaker 2: A grand minimum would be a double-edged sword. It might mean fewer solar storms, something in our favour. But it could also mean a dramatic change in our weather. The previous grand minimum coincided with a period of brutally harsh winters in Europe and North America. So this is a sort of intriguing time, right? Because you can see maybe just the start of these big changes, but you can't quite see why they're happening, but there are potentially very big impacts if they do. Exactly. This data suggests that the sun is going through a major change, a global change on the sun. So in the long-term life of the sun, we'd love to know what's going on.
[00:56:20] Speaker 17: If this trend does continue, it may be evidence of a bigger cycle in the sun's behaviour that we've only just begun to glimpse.
[00:56:29] Speaker 2: But the sun works on such vast timescales, even several hundred years of data can give us only a tantalising clue. So we've been watching the sun for a few centuries, but we don't know what was happening when the pyramids were being built or when the dinosaurs were alive or a billion years ago. And we don't know what's going to be happening a billion years into the future, so we're just seeing this tiny, tiny sliver of the lifetime of the sun, and it's really hard to imagine that in this enormous timescale. And that's the big challenge that lies ahead for solar scientists. What's emerging is that even the pattern we thought we knew, the 11-year solar cycle, isn't the full story. There are bigger, longer-term patterns in the life of our sun, and they could have profound influences on our planet and on us.
[00:57:48] Speaker 1: What's incredibly exciting is just how quickly our knowledge of the sun is growing. And thanks to huge technological and scientific advances, its surprises are gradually being uncovered.
[00:58:00] Speaker 2: And next time you feel the sun warm your cheeks, or you admire a sunrise, it's worth remembering just how complex and wonderful our local star really is.
[00:58:30] Speaker ?: And next time you feel the sun. And next time you feel the sun. And next time you feel the sun. And next time you feel the sun. And next time you feel the sun. And next time you feel the sun. And next time you feel the sun. So now you feel the sun. And next time you feel the sun. And next time you feel the sun. And next time you feel the sun. And next time you feel the sun. And next time you feel the sun. And next time you feel the sun. And next time you feel the sun. And next time you feel the sun. And next time you feel the sun. And next time you feel the sun. And next time you feel the sun. And next time you feel the sun.
[00:58:52] Speaker 18: And next time you feel the sun is around. Three trillion trees blanket our world. From spectacular cherries in spring. To the golden maples of North America. And the strange looking baobab trees of Madagascar. They can bring us joy. And even keep us alive.
[00:59:24] Speaker 19: All these amazing trees around us. Give us the air that we breathe.
[00:59:29] Speaker 18: But what do we really know about their hidden world?
[00:59:33] Speaker 20: As you get closer to the tree. It just gets more and more remarkable.
[00:59:38] Speaker 18: In this series. We'll follow their incredible lifespans.
[00:59:43] Speaker 21: There are trees alive on earth today. That are as old as the great pyramids.
[00:59:48] Speaker 18: As you get older. Discover how trees communicate.
[00:59:51] Speaker 22: This whole wood is interconnected. And that opens up so many possibilities.
[00:59:57] Speaker 18: And learn how they survive. In some of the toughest places on earth. This time we're following trees as they reach adulthood. When they do the most extraordinary things.
[01:00:22] Speaker 19: But what's really incredible is that they're actually talking to each other. It's just amazing to see these explorers root. In the face of incredible odds.
[01:00:34] Speaker 23: Unfortunately it's been struck by lightning twice.
[01:00:37] Speaker 24: You had chimneys belching out. Smoke. Soot. And this tree managed to deal with that.
[01:00:46] Speaker 18: You'll never look at a tree in the same way again. Soot. Arribing at adulthood is a major milestone in a tree's life. Some trees get there quickly. Apple.
[01:01:11] Speaker ?: Pear.
[01:01:12] Speaker 18: And cherry trees. Bear fruit as young as five years old. It's a visible sign that they've reached maturity. Others, like the slow growing hemlocks of North America. Can take up to 300 years to become an adult. And once they're mature. Some species like this olive tree. Can be in their prime for a thousand years or more. These adult years are the busiest of a tree's life. Tree guru Tony Kirkham spent 40 years working at Kew Gardens. He's visiting one of his favorite trees. An English oak.
[01:02:20] Speaker 19: This is a lovely oak tree. It's probably around 75 years old. It's gone through the teenage mode. It's gone through adolescence. And it's coming into adulthood now.
[01:02:39] Speaker 18: And rather than slowing down at 75, this tree is just getting going.
[01:02:48] Speaker 19: Unlike us people, where we get to a certain age and we stop growing, we may put a little bit more weight on as we get older. A tree is dead opposite to that. Trees continue to grow. So it's putting on about 50 centimeters a year in height and spread. And with that, more leaf. So this is all this year's growth. So it's fresh, fresh shoots. And this is growing pretty fast, this tree.
[01:03:21] Speaker 18: Tony is visiting at the beginning of the day. An especially important time for a tree. To prepare for the day ahead, this oak is doing something surprisingly familiar. It's stretching.
[01:03:42] Speaker 19: It's getting ready for a hard day's work. Those branches lift by about 10 centimeters in preparation for catching that sunlight.
[01:04:04] Speaker 18: Experts have only recently discovered that trees sleep at night, relaxing their branches down. Then, just before dawn, they raise them up. And angle their leaves towards the sun. Ready to create the food they need to grow taller and stronger through adulthood. As this oak wakes up, so do more than 2,000 other species of living things that call it home.
[01:04:45] Speaker 19: The oak plays host to the most different living organisms of any other tree in Britain. It's from mosses, lichens, insects, mammals, birds. A whole range of living things. It's a high rise zoo for all these species. It's in pretty good condition and hopefully this tree will be around for several hundred years.
[01:05:20] Speaker 18: Every tree on earth has lodges. Countless creatures who live amongst their leaves and branches. Many just want a safe place to stay the night. But some need the tree for their survival. Beetles burrow beneath a tree's bark. Woodpeckers may look beautiful, but they inflict serious damage in their search for food.
[01:05:58] Speaker ?: It's in pretty good condition. It's in pretty good condition. It's in pretty good condition.
[01:06:02] Speaker 18: Unable to run away from these pesky pests, trees have developed some ingenious ways to defend themselves. And one of the most remarkable is communication. Incredibly, trees can talk to other trees and warn them when they're under attack. Professor James Logan is at Broadwoodside near Edinburgh. He's an expert in how living things communicate.
[01:06:43] Speaker 25: Any time that I'm around trees, I'm in absolute awe. They're the geniuses of nature in many ways and they do it in such a secret way. I'm in this fantastic avenue of hornbeam trees. These trees are about 24 years old and there couldn't be a better place to come to explore how trees communicate with each other. When we think about communication as humans, we think about everything that we're seeing or that we're hearing around us. Trees obviously don't have eyes and they don't have ears, but what they do have is the ability to produce smells, chemicals in the air. And as I'm standing here under this tree, this tree is producing loads of chemicals. There's an aerial soup of chemicals around me that this tree is using to communicate with.
[01:07:36] Speaker 18: The smelly messages from the tree start when a caterpillar, or larger animal, chomps on one of its leaves. Remarkably, the tree knows it's an animal disturbing its leaf, rather than just the wind, because it's able to detect the attacker's saliva as it chews.
[01:08:00] Speaker 25: When they start to get munched, what's happening inside the tree is it initiates a defence system. So the tree starts to produce chemicals that actually taste really bitter to put off the insects. What's really incredible is that when this leaf is being attacked, it's sending a signal to the rest of the tree. So all the leaves on the tree start to produce the same types of chemicals that make it taste really bitter to protect the entire tree.
[01:08:26] Speaker 18: But it doesn't stop there. The alarm call is carried even further on the breeze.
[01:08:35] Speaker 25: When this tree is being attacked by insects, not only is it sending out signals to protect itself, but it's actually sending out signals to the tree next door. Now these two trees might be metres and metres apart, but actually that tree is communicating with this tree. They're actually talking to each other. This tree is sending out a chemical signal telling this tree that it's being attacked. So this tree actually receives that signal and starts to produce the same chemicals as if it was being attacked to protect it as well. Every tree in this avenue will be picking up on the same signals. It's almost like a highway of information.
[01:09:27] Speaker 18: And sometimes we can smell the signals ourselves.
[01:09:34] Speaker 25: If you walk into a pine forest, you know, you're hit with this amazing smell of pine.
[01:09:41] Speaker 18: The familiar scent is in fact our noses detecting the chemical alarm calls released by the trees. And without even realising it, we could be benefiting from them.
[01:10:01] Speaker 25: We've all heard about getting out into nature to do us some good. And if you walk into a forest, there's something quite pure about the smell. It feels like it's cleansing you. But there is actually some scientific evidence to this because some of those chemicals have been shown to have a really good effect on our health, lowering our stress, being good for our mental health. And I tell you what, this is good for the soul.
[01:10:27] Speaker 18: Trees in the prime of adulthood may look static, but they're buzzing with activity. And they're flourishing in landscapes across the globe, even in our cities. But how do some of the eight million trees in London beat the odds to thrive for 300 years or more? Trees can flourish in some truly remarkable places. Including our very busiest cities. In America, around five and a half billion trees line its streets and parks. Providing shade and colour amidst the urban grey. One of the world's leafiest cities is London. The UK's capital has nearly eight and a half million trees. Almost as many as there are people. In spring, its streets erupt in pastel pinks. And reds and golds brighten up an autumn day. But what does it take for a tree to thrive in the urban jungle? Historian and Londoner Josh Levine is tree hunting on Cheapside, one of the capitol's oldest streets.
[01:12:25] Speaker 24: Here, emerging out of the city of London, is a tree. And it's much older than all of these buildings that stretch down here.
[01:12:40] Speaker 18: This is a London plane tree known as the Cheapside Plain. Josh thinks it's the oldest tree in the city of London. But he has the pictures to prove it.
[01:12:57] Speaker 24: This is going back to the 19th century. And it gives you a real sense of how this must have been going way back. With the tree looming over, as the tree still does, you can see the horse and carriage. You get a sense of just how different everything was.
[01:13:17] Speaker ?: The images date back over two centuries.
[01:13:18] Speaker 18: So Josh believes the plane tree was planted around 300 years ago.
[01:13:28] Speaker 24: It is from some time in the 18th century. We don't know when exactly. But we know that by 1841, people were talking about it as though it was a venerable tree, a magnificent landmark.
[01:13:42] Speaker 18: What's amazing about this tree is that it's endured everything London has thrown at it. Especially the city's grime.
[01:13:54] Speaker 24: If you think about Victorian times, you had the most polluted atmosphere. You had chimneys belching out, smoke, soot. And this tree managed to deal with that.
[01:14:08] Speaker 18: Three centuries ago, Londoners discovered that plane trees can thrive in places where pollution chokes other trees. Josh can reveal how they've flourished for so long.
[01:14:25] Speaker 24: And here we are really close up to it. I mean, you can look at it in all its gnarled glory. And what was so great about them, the reason they survived, was because of this. Their bark.
[01:14:43] Speaker ?: The bark comes off.
[01:14:44] Speaker 24: So in an area like London, which was, think about it, you know, in Victorian times, absolutely filthy. What could survive here? I mean, people could barely survive here. A tree that could survive was this one. Because the impurities would go into the bark, into the covering, and then it would fall off. And it could rejuvenate. It could live again.
[01:15:10] Speaker 18: All year round, plane tree bark flakes away, taking the pollution with it and revealing fresh growth beneath. This process allowed the Cheapside Plain to survive the 65-year-long Victorian era, when pollution was at its peak. But another challenge came four decades later. To explain, Josh needs to climb to the height of the tree's canopy.
[01:15:57] Speaker 24: I've got a view that you just don't normally see. It's a great way to see the tree. I mean, there's the tree down there. And then there's this astonishing site. This is St. Paul's Cathedral.
[01:16:10] Speaker 18: During the Second World War, this area was devastated by German bombers. Aerial photographs taken in 1945 reveal the aftermath of the Blitz.
[01:16:24] Speaker 24: And you can see the total devastation. You can see things have been flattened everywhere.
[01:16:31] Speaker ?: So what's left? St. Paul's. It survived.
[01:16:35] Speaker 24: And the other thing here to have survived is just below us. It's the tree.
[01:16:46] Speaker 18: St. Paul's. St. Paul's is a famous symbol of London's wartime resistance. But the Cheapside Plain is an equally lucky and special survivor. Today it's one of more than 100,000 London planes that line the capital's streets. From Westminster to Wembley. It's believed that every year London's trees combine to remove nearly two and a half million tons of pollution from the air.
[01:17:26] Speaker 24: Let's face it, living in London has always been difficult. But a tree that's able to adapt to the circumstances, a tree that's able to rejuvenate itself, that's the one that's going to do well in London.
[01:17:38] Speaker 18: There are 70,000 different species of tree on the planet. And many of them have found remarkable ways to adapt to their landscapes. On the edge of the Arctic Circle, the temperature can drop to minus 45 degrees. But this icy world is still home to willows and birches. And they've found a special way to survive. These are dwarf willows and dwarf birches. There are entire forests where no tree is more than a metre tall. Being close to the ground protects them from the worst of the freezing winds and helps them to survive. At the opposite extreme, in the dry, dusty plains of North America, the roots of jacaranda and juniper trees spread up to 30 metres away from their trunks in the hunt for water. So remarkably, these trees can grow flowers, even in the middle of a desert. Even the more hospitable landscape of Italy is home to a tree that has adapted to survive. The elegant Italian cypress. Nestled in the rolling landscape of Tuscany is a vineyard that produces the world-famous Chianti wine. It's owned by Count Sebastiano Caponi, the 20th generation of his family to look after this land.
[01:19:54] Speaker 26: The cypress trees have become kind of an icon of the Tuscan landscape. People, when they come to Tuscany and they see the cypress line drives, they fall in love with it. The drive was planted by my great-grandfather, Piero Caponi, around the end of the 19th century and beginning of the 20th century. Every time I come home and I see these beautiful trees, it's definitely a wonderful and warm welcoming for me.
[01:20:20] Speaker 18: Cypress trees have been planted in Italy since before the Romans, 2,000 years ago, to mark boundaries and to protect buildings from the wind. Adult cypresses are long living. They can survive up to a thousand years. And they have a remarkable ability to protect themselves from a particular enemy.
[01:20:49] Speaker 26: Wildfire. We had a couple of fires two years ago due to the drought and we have to be careful, you know. We have to be careful because a single spark in a matter of minutes and hours will burn down acres and acres of woodland.
[01:21:08] Speaker 18: But the clever Italian cypress uses fire to its own advantage. Like pine or fir trees, they grow cones to hold their seeds. But the cypress has two different types of seed cone. The first opens to release its seeds as soon as they're ready.
[01:21:40] Speaker 26: You see all those cypress cones, the kind of mature ones are the brown ones. Yeah, these are the open ones. This is the typical you find on the floor in the woods, you know. Once they open, the birds will come and they will spread the seed around and then new saplings will grow.
[01:21:54] Speaker 18: But there's a second, special cone that has developed to deal with wildfires.
[01:22:01] Speaker 26: The fire ones are the closed ones. They can stay shot like that for many, many years. You can see this is a mature one over here and they will open up only at very, very high temperatures.
[01:22:15] Speaker 18: As our summers get hotter, this landscape is increasingly vulnerable to the threat of wildfire. Whilst the trees themselves will die in a fire, the intense heat opens up the special cones. So the seeds, usually sealed inside, are released. And new cypress trees can grow tall in the landscape.
[01:22:43] Speaker 26: I think the major ability of Italians is to create beauty. And this is a part of that beauty. These trees are part of that beauty. And Tuscan would be a very different thing without them.
[01:22:58] Speaker 18: Trees in the prime of adulthood really do the most extraordinary things. But what we can see above ground is just the beginning. We'll discover that it's below the surface where the tree is hiding its greatest secrets. The rolling countryside of southern England is home to majestic oak, ash and beech trees, many hundreds of years old. Like most trees, we can only see them above ground. But this seemingly normal hedgerow holds something intriguing beneath it. Tree expert Tony Kirkham is entering a mysterious underworld. To understand what's happening below the surface of a tree.
[01:24:10] Speaker 19: This is Hell Lane in Dorset. It's a hollow way. And basically it's a sunken lane. The trees line either side. They're growing over and they join in the middle creating this secret tunnel. It's very atmospheric. It's mystical, it's magical.
[01:24:39] Speaker 18: This ancient pathway was created over centuries as thousands of people walked across the land. Pushing the soft sandy soil in between the trees lower into the landscape.
[01:24:54] Speaker 19: The great thing about this place is that you can see tree roots. I think they fascinate me so much because they're underground, they're out of sight. We don't see them. It's a hidden life of a tree.
[01:25:10] Speaker 18: A tree's roots defend it from one of its great enemies.
[01:25:16] Speaker ?: The wind.
[01:25:22] Speaker 18: Trees can flex and bend in a breeze. But as they grow taller, they become more vulnerable to the impact of the wind.
[01:25:34] Speaker 19: So here we have a tree that's about 15 to 20 metres tall. And these are ash trees. And everybody would believe that below ground would be a mirror image of what we see above ground in order to support that height and stop it blowing over on a windy day like today. But actually that's a myth. And tree roots are very shallow.
[01:25:58] Speaker 18: Surprisingly, most tree roots grow sideways, just below the surface.
[01:26:04] Speaker 19: It's about the tree roots gripping the soil. So you can see this amazing root, this amazing lateral anchor root. That's an anchor root. And the primary objective of a root is to support that tree, to stop it blowing over and for it to be able to grow tall and reach up into the sky.
[01:26:24] Speaker 18: Even as adults, trees keep growing taller. And they continue to grow new roots exactly where they need them.
[01:26:33] Speaker 19: As the trees move in the wind, like on a windy day like today, as they move, the tree sends signals down to the root system saying, "I need more roots on this side. I need more roots on this side." The different parts of the tree talk to each other and create these roots.
[01:26:56] Speaker 18: But roots aren't just anchors. A growing tree has up to 30 miles of them to take up water and nutrients from the soil. The thirstiest trees can suck up three and a half thousand litres of water a day. Enough to fill nearly 20 bathtubs.
[01:27:20] Speaker 19: So this is a lateral root coming off the main anchor root. We have these laterals coming down. They will produce these more fibrous roots that have the ability to absorb moisture. Most trees, the root systems are a maximum of a metre deep. In fact, about 90% of tree roots are in that top 10 centimetres, where there's lots of water, oxygen, nutrients. And as a tree grows, that lateral root system will grow with the tree.
[01:27:53] Speaker 18: Some adult trees can have as many as five million fibrous root tips to nurture them. And whilst the parts of the tree we see above the surface weigh five times more than their roots, it's these hidden underground heroes that are performing the most incredible feats.
[01:28:15] Speaker 19: It blows my mind all the time, even though I've been working with trees for 50 years, still fascinates me how they stand up.
[01:28:27] Speaker 18: Trees in their prime can thrive in many varied landscapes. Some stand tall as magnificent loners. Others grow in long, majestic avenues. And perhaps the most atmospheric of all, in vast woodlands. The Woodland Trust's Kylie Jones Mattock looks after a collection of trees near the North Wales coast. It's a rare piece of forest that really comes to life in the autumn.
[01:29:15] Speaker ?: It's an amazing place. It's a place full of life.
[01:29:21] Speaker 22: It's an ancient place too. I really love this time of year. In October, the leaves are just starting to turn. These individual trees, on their own, each tree isn't that old. But there have been trees growing together here for hundreds, if not thousands of years. And when a woodland has been that well established, really special things start to happen.
[01:29:56] Speaker 18: When trees grow together in a woodland, they can do something extraordinary. Use their roots to share water and food with one another. But this act of generosity only happens with the help of a go-between. And it's in the autumn that it starts to reveal itself.
[01:30:18] Speaker 22: Just as the trees are starting to close down for the autumn, the fungi show their true colours. They bring us this splash of colour and they come in purples and reds, colours that you don't see in nature as often. You get to this glimpse into the hidden world of the forest.
[01:30:47] Speaker 18: Whether they're toadstools, mushrooms, or puffballs, fungi can seem otherworldly. But what we see is just the tip of the iceberg. Beneath the surface, there's a much larger part of the fungi that spreads far and wide across the forest floor.
[01:31:24] Speaker 22: Just by lifting a rock, you can really lift the lid on the hidden world of the forest. Intertwined with all these roots are a network of microscopic fungal threads. They intertwine with the roots, wrap round them, even penetrate them. This whole woodland here is absolutely riddled with fungi, twisting and interconnecting beneath our feet. And these tiny threads enable the trees to get to places they couldn't otherwise reach.
[01:32:01] Speaker 18: The fungal threads attach themselves to a tree's roots and help it gather the nutrients it needs from the soil. Experts like Kylie are only just beginning to fully understand how much trees rely on this incredible fungal network. Because the threads also connect the trees to each other. They link one tree's roots to the roots of its neighbours. Binding hundreds of trees together.
[01:32:47] Speaker 22: What makes those links between all the trees in this forest over a vast area is this fungal network. Which means this whole wood is interconnected. A bit like a complex web of cables connecting the whole of this woodland. This whole wood is part of a wood wide web.
[01:33:09] Speaker 18: Some experts believe the trees could make use of this incredible hidden connection to support one another in times of need.
[01:33:19] Speaker 22: To help us visualise this wood wide web, I'm going to have a little go at recreating it with some low budget tech. So, these lights represent all the things that pass within the network between the trees.
[01:33:44] Speaker 18: Because the fungal strands link the roots of different trees, the fungus could move nutrients from one tree that's doing well to a neighbouring tree that can't find enough food on its own.
[01:34:03] Speaker 22: For example, a small oak seedling like one of these growing under the shade is going to struggle to survive. But the parent tree can actually channel nutrients, sugars to that young sapling so it can survive and thrive in the forest just waiting for its chance to grow up into the canopy.
[01:34:25] Speaker 18: One cubic inch of soil can hold as much as eight miles of fungal threads and the connections could spread for miles. So, if a tree on the far side of the woodland is struggling for water, trees with plenty on the other side could share what they have.
[01:34:46] Speaker 22: The other trees in the forest could be using their fungal network to support that tree to ensure it survives. It's a fantastic system and we're really just on the verge of understanding all the things that this wood web achieves.
[01:35:02] Speaker 18: This woodland is a community, an entire forest of trees that could potentially be sharing resources, allowing each other to thrive, all via hidden connections we never see.
[01:35:17] Speaker 22: We just have no idea what the potential is, but we do know that these connections are going to be incredibly important to the health, the resilience, the survival of our woodlands as they face challenges in the future.
[01:35:30] Speaker 18: Trees have astonishing ways to flourish, even in our changing world. And when they're harmed by forces they can't control, they can even heal themselves in the most surprising and ingenious ways. Have you ever been among birch trees and looked closely at their trunks? They're dotted with what look like eyes that follow you through the forest. These are scars, reminders of whole limbs that have been lost in the past. And they are the perfect example of how adult trees can heal themselves. It happens as trees get taller. When new branches grow higher up, their leaves block sunlight from reaching those on the older branches below. So the tree deliberately amputates the old branches by cutting off their food supply. And they fall away, leaving behind the eyes. But what happens when trees are harmed by forces they can't control? Whether it's a violent storm, a run-in with a grumpy elephant, or even a bear with an unscratchable itch. Injuries are an inevitable part of a tree's life. If there's one place to be a wounded tree, it's at the Royal Botanic Gardens at Kew. This world-famous sanctuary in London looks after 2,000 different species of tree. From all over the planet. Cecily Withall is a member of Kew's tree gang. The equivalent of an on-call doctor service. This morning she's doing her daily rounds.
[01:38:16] Speaker 23: Things like lightning, wind, or even human intervention can harm a tree. It's really important for us, as a unit in the tree gang, to really make sure that these trees are, one, safe for the public, to be looking at them and being around them, but also maintaining them so that they have huge longevity in front of them, make sure that they can outlive our time here, which is the most important thing.
[01:38:42] Speaker 18: First stop on Cecily's round is a rather extraordinary patient.
[01:38:52] Speaker 23: This tree was planted in 1814 and is a Corsican pine. Classed here at Kew as one of our unluckiest trees.
[01:39:04] Speaker 18: At 30 metres high, this pine towers over the trees around it. But it's height means it acts like a lightning rod for any passing storm.
[01:39:20] Speaker 23: Unfortunately, it's been struck by lightning twice. Trees don't really have a defence mechanism to stop them being struck by lightning. If a tree is struck, it can die instantly. 50% of strikes will kill a tree. When lightning hits a tree, the water internally in the trunk and the stems will completely turn to gas instantly.
[01:39:48] Speaker 18: The extreme power of a lightning strike, up to 300 million volts, can split an entire tree in two. Luckily, the Corsican pine survived. The lightning only travelled down the outer edge of the tree.
[01:40:08] Speaker 23: What we can see from the damage on this tree is just bark. You can see on the front of the bark where it's exploded off of the main trunk.
[01:40:17] Speaker 18: Like human skin, a tree's bark is its first line of defence. A tough outer layer that shields the vulnerable wood beneath. And when a wound does go deep, the tree seals around it, stopping any infection before it can cause more damage.
[01:40:39] Speaker 23: They might not be able to completely get rid of the wound itself, but fortunately for us, the trees stopped that wound becoming any larger. The tree really is its own doctor and can heal and seal those wounds away so they don't spread throughout the rest of the stem.
[01:40:57] Speaker 18: But this unlucky tree hasn't just survived two lightning strikes. Nearly a hundred years ago, it was hit by a small aeroplane.
[01:41:11] Speaker 23: The aircraft itself was seen to remove the top of the tree, hit the canopy and a limb came down and ripped the bark off.
[01:41:19] Speaker 18: Luckily, the pilot survived. And the tree sealed off the injury. At 211 years old, this Corsican pine is a true survivor. Like so many trees across our planet, it's doing extraordinary things to thrive in its prime.
[01:41:49] Speaker 23: So the tree is named the unluckiest tree at Kew, but I really don't think so. I think if it's managed to survive two lightning strikes and a plane hitting the canopy. It's still here growing strong. I think it's pretty special.
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[01:43:22] Speaker 19: All these amazing trees around us give us the air that we breathe.
[01:43:27] Speaker 18: But what do we really know about their hidden world?
[01:43:31] Speaker 20: As you get closer to the tree, it just gets more and more remarkable.
[01:43:36] Speaker 18: In this series, we'll follow their incredible lifespans.
[01:43:41] Speaker 21: There are trees alive on Earth today that are as old as the Great Pyramids.
[01:43:46] Speaker 18: Discover how trees communicate.
[01:43:49] Speaker 22: This whole wood is interconnected, and that opens up so many possibilities.
[01:43:56] Speaker 18: And learn how they survive in some of the toughest places on Earth. So far, we've learned how even the mightiest trees begin life as tiny seeds. And we've followed them as they thrive through their midlife years. In this final episode, we'll meet the surprisingly sprightly elder statesman of the tree world.
[01:44:28] Speaker 22: As trees get old, they get really exciting.
[01:44:32] Speaker 19: When the old tree's had enough, that newly-rooted branch can start to grow.
[01:44:38] Speaker 18: And we'll join them through the final stage of their remarkable journey.
[01:44:43] Speaker 21: When a tree dies, you get to see its past life.
[01:44:48] Speaker 20: It may look dead, but actually, it's doing far more than the eye can see.
[01:44:55] Speaker 18: You'll never look at a tree in the same way again. Trees are extraordinary for so many reasons. But possibly the most amazing to us is their incredibly long lifespan. They say it takes an oak tree 300 years to grow. 300 years to live. And 300 years to die. But this third chapter in a tree's long life is full of surprises. Especially when some of the oldest trees on the planet can live for nearly 5,000 years. But how do you tell the age of a tree? Professor Mary Gajan from Swansea University investigates the life stories of ancient trees.
[01:46:17] Speaker 21: Trees are just absolutely wonderful things. They're some of the biggest, most majestic natural things that we see in our environment. And they also grow with us. A tree that's small when we're small will be a big, tall, majestic veteran as we age. And that way that trees grow is really important. Because it means that we can find out things about that tree's life history. From looking inside them. So we've got this lovely healthy sycamore. They're a really common tree in our woodland. And looking at it, we can tell a few things about it. It's health, it's history. But if I want to know more about what it's experienced, I need to look inside the tree trunk. And we use this to take a small core from inside. So there's a little bit of hard work to get the core sample out.
[01:47:17] Speaker 18: For a tree this large, having a core taken is just like us getting a blood test. The tree will soon seal over the small hole.
[01:47:28] Speaker 21: I'm going to pop this in to slide underneath the core. Nice. Lovely core then. And it's just really small. So what I can see is what look like stripes inside this little piece of wood. And they are the growth rings. Trees don't grow in a haphazard way. They grow one ring every year. And time is marked through this core in these series of light and dark bands.
[01:48:01] Speaker 18: The faster growth of spring makes a lighter colored band. Slower growth in late summer and autumn makes a darker band. 365 days of the tree gathering sunshine. Making its food and growing bigger and stronger. All compressed and recorded in light and dark rings. Counting the number of these rings tells us the exact age of a tree.
[01:48:35] Speaker 21: So that history is hidden inside its trunk. Everything that has gone on in its long life.
[01:48:43] Speaker 18: But tree rings don't just mark the passage of time. They can also reveal something remarkable. A tree's memories. Because not every ring is the same size.
[01:49:00] Speaker 21: Where you see a wide ring. Something good has happened to this tree in that year. Maybe it was very sunny. There was lots of water. And the tree was able to grow a lovely wide tree ring. And that history of what's gone on in the woodland. It's almost like a diary that the tree records as it grows through time. And we can have a look at that diary and read it.
[01:49:27] Speaker 18: Incredibly, tree rings can offer glimpses into specific events in our history. And reveal how the tree reacted to them.
[01:49:39] Speaker 21: This is a piece of oak from the south-east of the UK. And this tree died in 1982. And the outside rings are nice and wide. We can see 1982, 81, 1980, 79, 1978, 77. And then we reach, in 1976, there's suddenly an incredibly narrow ring.
[01:50:03] Speaker 18: In 1976, the UK was hit by the worst drought for 250 years. For the nation's trees, it was a battle for survival. As they competed for the scarce water that remained underground.
[01:50:22] Speaker 21: It was an incredibly dry spring and summer. And thousands of trees didn't survive that drought. But this tree's a real survivor. It managed to hang on, even though it could only grow a really narrow ring.
[01:50:35] Speaker 18: This traumatic drought left its scar in the form of the narrow ring. But what's really interesting is what the tree did next.
[01:50:45] Speaker 21: Its neighbours probably didn't do so well and died. Because in the years after 1976, this tree grows really wide rings to take advantage of that space as it recovers from that drought.
[01:51:02] Speaker 18: After the drought, this stump's remarkable diary was recorded how the tree responded to it with six years of healthy growth.
[01:51:13] Speaker 21: So the trees have memory. In some sense, the rings inside their trunks are their memory. Trees are all individuals. And this one was able to recover quickly and grow wide rings. But not all trees do that. Sometimes those traumatic events stay in the tree's memory for decades and decades. You see the memory of that recovery in years and years of slower growth and narrower growth as the tree gives itself time to get over that event.
[01:51:50] Speaker 18: Scientists are only just beginning to understand how long tree memories can last. And even if these lessons in life could be passed on to the next generation.
[01:52:05] Speaker 21: One of the most useful things about looking at how a tree like this has responded to a drought in the past is that it gives us clues about how trees might respond to droughts and to extreme events in the future as our climate changes.
[01:52:21] Speaker 18: So if trees could learn from events in their past, what other secrets do they keep for an incredibly long life? And which trees have survived to become the oldest living things on Earth? This is Traquare House. Scotland's oldest continually inhabited home. It's hosted passing kings and queens for over 900 years. And in its grounds are Europe's longest living trees. Yews. Yew trees can grow up to 20 metres tall. And their canopies of evergreen, needle-like leaves can spread across 300 square metres. Expert Tony Kirkham has come to uncover the tricks these trees use to reach a ripe old age.
[01:53:37] Speaker 19: I know I have many favourite trees, but this is one of my favourites. And many people think it's quite a boring tree because it's green, you know, it's just a bank of green. It looks pretty bland from outside, but actually when you get inside, I think you'll be in for a real surprise. Oh, wow. Wow. It's cathedral-like. You come inside and it's like being inside a room of trees. Yeah, it's quite special. All you can hear is a wind coming through that upper canopy. And the light, the shimmering light, playing tricks on your eyes. It's going to be good to explore this.
[01:54:48] Speaker 18: This yew tree is an estimated 1,000 years old. It would have been a young sapling when William the Conqueror invaded England in 1066. As a mature tree, it's vast and has grown a huge umbrella-like canopy consisting of millions of tiny leaves.
[01:55:10] Speaker 19: One of the interesting things about this tree that allows it to live for so long is that every part of the tree is toxic to humans, animals and birds. So the leaves, the branches, the bark, the wood.
[01:55:25] Speaker 18: The fact they're so poisonous means yews have been linked with death for thousands of years. It's why graveyards are home to many of the UK's oldest yews. And because few creatures can harm them, the trees just get on with growing bigger. Over time, this tree's branches have entwined with other yews. As more than 900 years old, they're only now considered mature trees. And could live for another 2,000 years. But they face a big problem. As they grow taller and sprout more branches, their trunks will grow wider to support the extra weight. Eventually, the trunks will get so wide, they will start to rot. From the inside out.
[01:56:30] Speaker 19: Unfortunately, most of the ancient yews in the British Isles, the centre's rotted out, so they're hollow.
[01:56:39] Speaker 18: But these trees already have a plan for extreme old age.
[01:56:44] Speaker 19: Yews are amazing trees. And if you imagine that, you know, there's a trunk and these long sweeping branches are the arms or the legs of the yew.
[01:56:57] Speaker 18: Before its main trunk rots away, this wise old tree has changed the way it grows its branches. Rather than growing up, they're growing sideways and then downwards.
[01:57:11] Speaker 19: This is where this huge branch, it's come all the way from the main trunk, which is probably about eight or nine metres. And you can see here, it's touched the ground. Where the branches touch in the ground, it's generated roots, so it's independent. It's now got its own root source and this is a separate plant, but identical to the original parent.
[01:57:32] Speaker 18: Over the next few hundred years, the tree's strategy is to stop maintaining the old trunk and let it rot away entirely. The newly rooted offshoot will become the new trunk of the tree.
[01:57:46] Speaker 19: This next phase where the tree is growing out will be the second generation of this tree. And it will be self-sufficient on its own root system and will no longer need that parent trunk to survive. It's a fantastic thing to see.
[01:58:07] Speaker 18: With its new trunk, from which it will eventually grow more branches, this tree is essentially moving. Very, very slowly. Around a metre every century.
[01:58:20] Speaker 19: Most people think that trees stay put and they're in one position, but they're not. They're not static things. This is a walking tree, it's no longer static, it's heading south. So the yew tree is adapted to be long-lived. A tree that's been around for a long time and likely to be around for a lot longer.
[01:58:56] Speaker 18: In a warmer corner of Europe, there's another tree that proves getting old doesn't necessarily mean slowing down. The sun-soaked coastline of Puglia in southern Italy is the perfect place for olive trees to thrive in their sunset years. Antonio Antico's family has farmed olive orchards here for generations.
[01:59:30] Speaker 27: I work here with my father, with my grandfather, and we've been here for a lot of time. But the trees are here so much longer.
[01:59:39] Speaker 18: Puglia produces half of all Italy's olive oil. 40 million trees grow in an area smaller than Wales.
[01:59:52] Speaker 27: In this field probably we have more than a thousand trees and each one has different ages.
[02:00:00] Speaker ?: We have more than a thousand trees.
[02:00:02] Speaker 18: We have more than a thousand trees. Olive trees are fantastically well adapted to the hot and dry Mediterranean climate. They're evergreens, keeping their leaves all year round. The leaf's silver sheen is thanks to tens of thousands of tiny hairs, which trap moisture. So they stay cool and hydrated in the sunshine. The trees take their time, growing extremely slowly. So slowly, it's thought their twisted trunks could be shaped by the spinning of the earth itself. And one gnarly beauty here is estimated to be more than a thousand years old.
[02:00:58] Speaker 27: This tree is one of the amazing trees of this place. You can see by its size, its shape is one of the oldest.
[02:01:08] Speaker 18: It's believed to be one of the oldest olive trees in the world. So, what's its secret?
[02:01:19] Speaker 27: These trees can live so long because when they grow older, they just get wider. So they are really resistant to any kind of weather.
[02:01:31] Speaker 18: As the centuries have passed, this tree has grown wider rather than taller. With its sturdy shape, it won't topple over in strong winds. And being short means it's also less likely to be struck by lightning.
[02:01:52] Speaker 27: When we grow old, we start to get weaker. The value trees, when they get older, they get stronger.
[02:02:02] Speaker 18: Scientists have only recently discovered that the older trees get, the faster they grow. But rather than grow higher branches that would break in the wind, they pack on the weight around their trunks. And because they are bigger, old trees are better for our planet too. The older they get, the more carbon they lock away in their wood. So the more they're helping to combat climate change. Incredibly, every year, this magnificent old statesman bears olives. As juicy as when it was a teenager.
[02:02:50] Speaker 27: It's so amazing to see that it's still alive and still produce olives. And we can get more oil with these trees.
[02:03:03] Speaker 18: After a long, hot day in the orchard, Antonio can enjoy olive oil from his favourite thousand-year-old tree. But in the surprising world of elderly trees, we haven't reached the limit yet. These are the White Mountains, 250 miles from Los Angeles in California. Home to the oldest living trees on the planet, the bristlecone pines. 3,000 metres high, this rocky terrain is bone-dry in summer and ice-cold in winter. So the trees grow incredibly slowly. Their trunks expanding by just three millimetres a decade. And rather than using valuable energy to grow a fresh set of leaves each year. Bristlecone needles last for up to four decades. 20 times as long as most evergreen leaves. The oldest bristlecone pines are an incredible 4,850 years old. Making them as ancient as the great pyramids of Egypt. In the world of ancient trees, there are even more magical places and unique species to discover. Ancient forests that sustain millions of different creatures. And we'll discover one remarkable tree that's been around for hundreds of millions of years. All over the world, if you know where to look, you can find the most incredible trees. From dragon blood trees growing on islands in the Arabian Sea. To something very special in the Andes Mountains in South America. A tree that's one of the oldest species on earth. The weird and wonderful monkey puzzle. Expert Tony Kirkham is at Benmore Botanic Garden in Western Scotland. To reveal the surprising secret behind this long living spiny specimen.
[02:05:55] Speaker 19: Wow now, this is another one of my favourite trees. The monkey puzzle from Chile. It is an incredible tree. It just doesn't look real. It looks plastic, but believe you me, it's not soft. And why do we call it the monkey puzzle? Because where it grows in Chile, there are no monkeys. But it was introduced in 1795 to the UK. And as it was growing, everyone wanted to see this plant. And a barrister looked at this tree and said, Wow, that is amazing. That would puzzle any monkey to climb it. And today it retains that name, the monkey puzzle. And if you try and touch this, it's pretty spiky. It is a prickly customer. And they've got these points on the end that, you know, would deter any grazing animal. So if you look at a tree like this with all this protection and armour, and you think, well, you know, why does it need all this? What animal is likely to feed on this?
[02:06:52] Speaker 18: The answer is monkey puddles are protecting themselves from dinosaurs. These trees have been growing on Earth for 200 million years.
[02:07:10] Speaker 19: Imagine if we were in this forest 200 million years ago. It was tall trees up to, you know, 50, 60 metres, and several thousand years old. And imagine those huge footprints of a dinosaur coming into this forest to feed on them. These long necks that would reach up into these canopies. And that's why these scale-like reptile, sharp-pointed leaves are there. They've evolved for protection from feeding dinosaurs.
[02:07:37] Speaker 18: Ancient trees designed for a prehistoric world. From one of the planet's oldest trees to one of its most ancient forests. The Amazon rainforest in South America has been growing for an estimated 55 million years. Today, 400 billion trees live in its tropical climate. Some of them are staggering 3,000 years old or more. The rainforest is home to the largest collection of living things on Earth. Three million different species, many found nowhere else, live among the trees. Five thousand miles from the Amazon, there's another patch of ancient rainforest. But its location may come as a surprise. Northwest Wales. It's looked after by the Woodland Trust's Kylie Jones Mattock.
[02:09:02] Speaker 22: Well, it's got to be one of my favourite places in the world. It's a temperate rainforest. But that doesn't really capture how magical it is. Many people really don't understand that we have such a thing in the UK. A temperate rainforest is a woodland where this sort of beautiful weather is quite unusual. It rains. It rains 200 days of the year.
[02:09:32] Speaker 18: It's believed that 5,000 years ago, rainforests like this covered a fifth of the whole of the British Isles. Now it exists in just 1% of the country. In precious pockets of ancient woodland. It's like a piece of the Amazon in miniature in the UK. Formed over thousands of years, these woodlands are bursting with life. Much of it living on centuries-old trees. Like this giant sessile oak.
[02:10:14] Speaker 22: As trees get old, they get really exciting. That last third of a tree's life is when they get really interesting. There are some really old, gnarly specimens. And they're really important. Because they create this whole world that supports so much other life.
[02:10:34] Speaker 18: Just like in the Amazon, the twisted old trees create a perfect habitat for other living things. Including plants and lichens found nowhere else in Great Britain.
[02:10:48] Speaker 22: The tree provides this little microclimate, this little micro-world for so many other species to grow.
[02:10:56] Speaker 18: A single oak like this can be home to around 2,000 different species. Busy beetles and bustling millipedes living among its many nooks and crannies.
[02:11:11] Speaker 22: To really appreciate the rainforest, you do have to get up close and personal. There's a whole new world that appears. The textures, the shapes, the colours.
[02:11:26] Speaker 18: This ancient Welsh rainforest has thrived for thousands of years. And it's still the perfect place for trees to live to a ripe old age.
[02:11:39] Speaker 22: That sense of tranquillity. The sense that you're also in a really ancient place. It's got to be one of my favourite places in the world.
[02:11:54] Speaker 18: No matter how many years a tree lives for, eventually it will meet its end. But like everything in the extraordinary long lifespan of trees, this last chapter can span entire centuries. So, how do trees die? Insects can kill them. Especially when they attack en masse. Extreme weather is another common culprit. But there's one killer that can wipe out entire species of trees. Disease. The south coast city of Brighton is home to what is now one of the UK's rarest native trees. The elm. Kerry Pickett is one of many locals who treasure the precious elms of Preston Park.
[02:13:08] Speaker 28: I think the thing about trees is that they have a very calming atmosphere. People get something from trees that is not actually tangible, but we're all drawn to them. I do think that people come to visit the park to see the trees. People call it the People's Park and it really is because everyone is so proud of this area.
[02:13:38] Speaker 18: Elms can grow up to 40 metres, taller than a ten storey building. And a healthy tree can live up to 800 years.
[02:13:52] Speaker 28: The thing about the trees is that they're huge. What I like is the branches kind of look like they're coming back down to the earth, joining the earth again. It has quite a distinguishable bark. It's really crunchy. It's very tactile. You do want to stroke a tree when you see it like this.
[02:14:13] Speaker 18: Elms used to be a common sight across the UK. But in the 1970s, disaster struck. Dutch elm disease wiped out 90% of Britain's elms. Over 25 million trees. The disease is a microscopic fungus carried onto the tree by a tiny beetle. The fungus blocks the tree's circulatory system. Causing it to die from a lack of water. It's the job of Brighton's arboriculture manager, Peter Small, to protect the city's precious surviving elms.
[02:15:05] Speaker 29: We're hugely committed to preserving the city's trees. It is unique in terms of diversity and number of elms. There's nowhere else like it in the UK.
[02:15:19] Speaker 18: The key is to spot signs of infection before the beetle can lay its eggs.
[02:15:27] Speaker 29: This piece has had all the bark stripped off. The beetle will begin a journey underneath the bark along its central groove, laying eggs along either side. Each one of these tiny lines is a new beetle. And then they fly on to find the next bit of elm to repeat the process.
[02:15:49] Speaker 18: They've been fighting the disease in Brighton for over 50 years. For more than 90% of infected elms, the only solution is to chop the tree down. To stop the beetle and fungus from spreading.
[02:16:08] Speaker ?: I love trees.
[02:16:09] Speaker 29: I don't like felling them. It's devastating. Certainly for some people who've grown up with these trees since they were young. You know, people who were born in the city and remember these trees from their childhood.
[02:16:23] Speaker 18: And there's one tree in Preston Park that Peter is particularly keen to protect.
[02:16:30] Speaker 29: We believe it's the oldest English elm in Europe, over 400 years old.
[02:16:38] Speaker 18: This single ancient elm once had a neighbour. Together they were known as the Preston Park twins.
[02:16:47] Speaker 29: So you can see from the photograph a really nice shot of the twins. But the tree on the left was the other twin.
[02:16:56] Speaker 18: A few years ago, one of the twins caught Dutch elm disease.
[02:17:01] Speaker 29: That unfortunately was removed in 2019. Tragic loss.
[02:17:07] Speaker 18: The hollow trunk of the felled tree is now a poignant sculpture for locals to remember it by. But then, despite Peter's drastic action, the worst happened. The remaining twin also showed signs of the disease.
[02:17:27] Speaker 29: A couple of summers ago, there was an area of wilting, yellowing, on the very tips of a branch. That was confirmed to be a very early elm disease infection.
[02:17:39] Speaker 18: In an effort to save it, Peter's team cut away a huge area of the tree's canopy. For now, it survives.
[02:17:49] Speaker 29: The remaining twin, as you can see, is in good health. It's a solitary twin, but, you know, the name continues to be used. Fortunately, it's looking healthy and long may remain so.
[02:18:05] Speaker 18: No matter what disease or catastrophe it survives, the life of every tree must come to an end. But that's not the end of this story. What happens in the tree afterlife is extraordinary. Over the course of this series, we've followed the fascinating life cycles of our planet's trees. Every spring, colour blankets the earth. Turning to green as fresh leaves burst from branches. Then, as summer ends, the spectacle of autumn. Throughout their long lives, trees do remarkable things for our planet. They even help us to breathe. As leaves make sugar to fuel the tree, they breathe out oxygen. The vital gas that we, and almost every other living thing on earth, relies upon. But we don't just need trees whilst they're alive. Once they've died, they continue to help us. As they return to the place they came from. The soil. Scientist, Cecilia Reid, follows the journey of trees from life into death and beyond.
[02:19:58] Speaker 20: For many people, trees come to mean something very personal and precious. So it's no wonder we grieve its loss when it dies.
[02:20:09] Speaker 18: This is Betchworth Estate in Surrey, which tends to 100,000 trees. Most are doing well. But some, like this oak, have died. It's being left to decay naturally, which means people like Cecilia can appreciate its value after death.
[02:20:37] Speaker 20: We tend to think of oak trees as pretty sturdy, strong and resilient trees, which they are. But just like human beings, a few too many knockbacks can just completely destroy them. Its twisted branches and scarred wood tells us stories of a long, hard life.
[02:20:56] Speaker 18: After three centuries of life, this noble giant recently died of oak decline. A mix of stress, pests and diseases overwhelm the tree. To a point where it could no longer fight back. But after death, new life is moving in. To feast on the two dozen tons of wood the tree built up over the centuries.
[02:21:32] Speaker 20: As you get closer to the tree, it just gets more and more remarkable. Oak trees are known to host the most animals and living creatures in the UK. But even though this tree is no longer alive, there are still plenty of creatures, bugs, birds, all kinds of species that are making a home here. There are even these small little wasps. I can see two here that are actually burrowing, oh my goodness, into the hold.
[02:22:07] Speaker 18: These are parasitic wasps. Laying eggs into the hidden grubs of other insects, feasting on the tree. A grisly fate for a grub, but a sign of how much new life this single tree will generate.
[02:22:24] Speaker 20: It just goes to show how nature is definitely profiting from this great big guy who, even though he's dead, is still giving so much.
[02:22:35] Speaker 18: The hollows of a dead tree also offer safe places for large birds to nest. And other new life is also moving in.
[02:22:47] Speaker 20: If we look down here, we can see hundreds of fungi feasting away at the base of this tree. Life is literally finding a way to renew it, to reuse it, to kind of create its own renaissance. This striking skeleton of a tree will soon start to lose its branches. And then eventually the main trunk will fall down as well, becoming something we call fallen dead wood. So here we have a fallen piece of dead wood and it does look pretty old. I mean, the kind of rusty, like, iron colours are seeping through, giving it this lovely autumnal, aged look. So this dead wood, as we can see, it's on the ground, it's connected with the earth, with the soil. Wood decomposition is an essential recycling process and also a really natural part of every tree's life.
[02:23:49] Speaker 18: It can take 50 years for a dead tree to fall and another century to decompose. And that process takes an army of demolition experts.
[02:24:02] Speaker 20: This piece of fallen dead wood is being, bit by bit, eaten away by bugs, basically. And they play a really important role in digesting the dead tree's wood. These bugs will then become food for those animals such as maybe shrews or badgers or foxes. So we have this gorgeous recycling of life itself going on right in front of our very eyes.
[02:24:27] Speaker 18: Incredibly, 40% of the UK's woodland wildlife depends on dead wood. That's at least 5,000 different species. This is nature's way of recycling. The creatures feasting on the dead tree gradually break down every part of this once great oak. And the tree becomes part of the soil beneath our feet.
[02:24:58] Speaker 20: A single handful of forest soil can contain way more living organisms than the total number of human beings on planet Earth, which I think is absolutely remarkable.
[02:25:11] Speaker 18: Just as trees benefit our planet in life, their legacy continues in death.
[02:25:18] Speaker 20: The trees are a natural defence against global warming. The reason being is that they, on a daily basis, continuously absorb carbon dioxide and then they store that carbon in their body. When they die and start to decompose, it's helping to store some carbon safely away underground, protecting us and the surface of our planet from a dangerously warmer future. I think we owe these glorious ancient friends a big thank you. They are the ultimate cycle of life and the ultimate legacy.
[02:25:56] Speaker 18: We still have much to learn about the secret lives of many of the trees on Earth. But as we walk through a park in spring, visit a much loved family favourite, or stroll through an ancient woodland, we can stop to appreciate their incredible inner world. Trees are beautiful and fascinating. Above all, they're vital to our own lives, to our health and that of our precious planet. We'll see you next time.
[02:26:45] Speaker ?: We'll see you next time. Thank you. Thanks for joining us. We'll see you next time. Bye. Bye. Bye. Bye. Bye. Transcription by CastingWords