- 2 days ago
The dramatic life of the oak tree, a species that makes extraordinary transformations as it meets the challenges of the four seasons....
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00:00:00One tree is an icon of the British countryside.
00:00:04It is, of course, the oak.
00:00:11Today we begin an extraordinary experiment.
00:00:14We want to understand this species as never before.
00:00:18And to do that, we will film this one remarkable specimen
00:00:22for an entire year.
00:00:27Armed with the latest technology,
00:00:29we will investigate how our oak battles to survive
00:00:33through four very different seasons.
00:00:35In autumn, we go underground to see how its roots
00:00:39stocks up on precious resources.
00:00:41What we are looking at is a highly dynamic system.
00:00:45In winter, we discover the sophisticated strategies
00:00:48our tree uses to take on everything
00:00:50the elements can throw at it.
00:00:53In spring, we find out how it senses the world
00:00:57and how it even has its own form of language.
00:01:00It talks to itself as a chattering goes on
00:01:03across the whole canopy.
00:01:05And in summer, we'll see it fight predators
00:01:08hell-bent on eating it alive.
00:01:12Over the next 12 months, I want to see the world
00:01:15as our tree does and tell its amazing story.
00:01:19Wow!
00:01:21In the coming year, I can't predict exactly
00:01:23how well it will fare, badly or well.
00:01:26But I can promise you one thing.
00:01:28You will never look at an oak tree in the same way again.
00:01:54The oak we've chosen to follow for our year-long experiment
00:01:57stands in Whiteham Woods, just outside Oxford.
00:02:02It's a rather special tree.
00:02:06For a start, it's almost 400 years old.
00:02:10That means it was a sapling during the battles
00:02:13of the English Civil War.
00:02:16It was laying down its roots as Isaac Newton described gravity.
00:02:22And it matured as Britain underwent its Industrial Revolution.
00:02:29What's more, our oak is in a rather special place.
00:02:34In 1942, the University of Oxford acquired Whiteham Woods,
00:02:40our oak's home.
00:02:41Specifically so scientists could research British woodland.
00:02:46And I know these woods extremely well.
00:02:49I taught biology at Oxford for 20 years,
00:02:52and my students and I used to come and study
00:02:54the countless insects that live here.
00:02:59The climate, bird populations, the soil.
00:03:02Scientists know a lot about Whiteham,
00:03:05and this will help us better understand our tree
00:03:07and how it changes as we follow it through the year.
00:03:21Our year-long experiment begins in late August,
00:03:24and the first task is to assess our tree's condition.
00:03:28To do this, forestry scientist Dr Matt Disney
00:03:31and Dr Eric Casella will create an incredibly accurate
00:03:35three-dimensional map of our tree.
00:03:38This is done by firing almost two billion pulses
00:03:41of laser light at our oak.
00:03:47The end result is this beautiful image of virtual oak.
00:04:00A year from now it will help us find out how our oak has fared,
00:04:03how much it's grown and how much new wood it's made,
00:04:07even how much oxygen it's released.
00:04:14We get some information straight away.
00:04:17Our tree is some 90 metres tall and 30 metres wide.
00:04:22But for me there's another quite astonishing and quite unexpected detail.
00:04:30One of the really interesting things that we can get from these data
00:04:33is we can estimate the total number of leaves on the tree
00:04:36and then from that...
00:04:38Without counting them?
00:04:38Without counting them manually.
00:04:40And I'll tell you, I have manually counted leaves on an oak tree just recently
00:04:45and it's not a fun job.
00:04:47And being able to do it in an automatic way
00:04:49without getting your hands dirty like this is far preferable.
00:04:52How many?
00:04:53Well, we think that there are around 700,000 leaves on this tree.
00:04:58To me, the fact that you can tell how many leaves this tree's got is just incredible.
00:05:05How many?
00:05:06It's amazing, isn't it?
00:05:07The total area of those leaves is about 700 metres squared.
00:05:11So, to put that in a bit of context,
00:05:13that's about three tennis courts worth of leaf area.
00:05:19Our oak needs all these leaves because they capture sunlight,
00:05:23the source of all its energy.
00:05:27But now, in late August,
00:05:29our tree is acutely aware that sunlight will soon become a precious commodity.
00:05:41As autumn approaches, the days shorten and the temperature begins to drop.
00:05:52To survive, our oak must transform itself.
00:06:18It may look as if not much is happening, but all across our tree, a dramatic process is taking place.
00:06:25Our oak is beginning a colossal redistribution of its resources.
00:06:28Well, it's been through this process hundreds of times before, but each time is no less challenging.
00:06:39To see what our oak is really up to, we need to picture what's going on beneath its bark.
00:06:51As autumn begins, throughout all the branches and leaves,
00:06:55a hubbub of chemical messages are now being sent and received.
00:07:02These chemicals are known as hormones,
00:07:04and our tree is producing them to prepare itself for the autumn.
00:07:12Well, it may seem odd, but just like us, trees have hormones.
00:07:16These chemical messengers flow through the body of the tree,
00:07:20controlling and managing all sorts of important processes.
00:07:23In us, these hormones are responsible for some of the biggest changes we'll go through in life,
00:07:28like pregnancy and puberty.
00:07:30In our tree, they're responsible for an equally crucial change.
00:07:36As autumn gets underway, driven by hormonal signals,
00:07:40trees begin to break down pigments and nutrients in their leaves to store over the winter.
00:07:50They begin to eat themselves.
00:07:56The result is a spectacular change in the colour of the leaves.
00:08:04Once the nutrients have been extracted,
00:08:09trees like our oak will then start to shed their leaves to conserve water and energy in the coming months.
00:08:20But how exactly does our tree know when it's time to begin this huge change?
00:08:31For a very long time, people assumed changes in autumn were triggered simply by a drop in temperature.
00:08:38But what happens if there's an unusually cold spell in summer?
00:08:42How does our tree know not to drop all its leaves?
00:08:46It turns out that trees rely on a far more sophisticated method than temperature alone to sense the changing seasons.
00:08:55In their own way, they can see what's going on.
00:09:05Well, this should give you an idea of how most plants see the world.
00:09:09While you and I can perceive a wide range of colours,
00:09:12trees like our oak are only able to sense the red light in the spectrum.
00:09:17And they can do this thanks to an incredible chemical pigment in their leaves called phytochrome.
00:09:25Phytochrome, a substance in our oak's leaf cells, is incredibly sensitive to the red light that makes up part of
00:09:31the sun's rays.
00:09:36It's a kind of chemical stopwatch that is also able to measure the hours of sunlight and darkness.
00:09:44So as the nights get longer, the phytochrome acts like a signal telling the tree that autumn has begun.
00:09:53This means that all the hormones that prepare the tree for the cold months kick in at exactly the right
00:09:59time.
00:10:04It's now October and our tree is not only dropping leaves,
00:10:09it's also time for our oak to release its most precious cargo.
00:10:14Autumn is not just a time for preparing for the cold, it's also when our oak releases its offspring out
00:10:21into the world.
00:10:23We're all familiar with acorns, but this really is a masterpiece of evolution.
00:10:28Inside this little capsule is not only the genetic code to make one of these,
00:10:33it also comes packed with food and protection from the elements,
00:10:38meaning this seed has all it needs to survive the winter.
00:10:42To spread acorns, the tree relies on the help of animals like jays and squirrels,
00:10:47who often store them underground and then forget where they are.
00:10:54But the oak has an ingenious trick to improve its acorn's chances.
00:11:00It varies the number of acorns it produces from year to year.
00:11:04Some years there are thousands, others, like this year, there are very few.
00:11:13While acorns are the perfect food for our friend here,
00:11:16the fact that she can't rely on oaks all the time means she has to find other sources of food.
00:11:22But every five or ten years, oaks have what is called a mast year.
00:11:27They produce such a deluge of acorns that all the acorn eaters just simply can't cope.
00:11:32They're overwhelmed, no matter how hard they try.
00:11:34And this means that the chances of one acorn germinating and surviving
00:11:41becomes dramatically increased.
00:11:45With help from the local wildlife,
00:11:47at least one of our oaks acorns dropped this autumn is likely to germinate next year.
00:11:53And when it does, it will be a spectacular event.
00:12:03Fueled by nutrients locked up within the acorn, our tree's offspring is brought to life.
00:12:24A chute reaches upwards to find sunlight.
00:12:32While a root penetrates beneath to find water.
00:12:52In just a few months, this acorn has developed into an infant oak with its very own leaves.
00:13:04This tiny organism is now able to fend for itself.
00:13:17The success of the oak is largely dependent on the animals that help disperse its acorns.
00:13:24And there's one species that in the last 300 years has been particularly helpful.
00:13:32And that's us.
00:13:34In the 18th and early 19th century, there was a frenzy of oak planting in Britain.
00:13:42In just six years, it was reported that one military officer managed to plant 922,000 oaks.
00:13:52The reason for this surge was simple.
00:13:54Britain had the world's most powerful navy, and nearly all of her ships were made of oak.
00:14:04This is the HMS Victory, famous for defeating the French fleet at the Battle of Trafalgar.
00:14:11The ship is a product of almost 6,000 oak trees, reimagined by some of Britain's finest shipwrights.
00:14:25This vessel and hundreds like it were the reason for Britain's insatiable demand for oak.
00:14:35Climb inside and you see oak everywhere.
00:14:43This is the lower gun deck of the HMS Victory.
00:14:47Many of these sturdy oak timbers have been here since the ship first set sail in 1765.
00:14:53At night, hundreds of men would sleep jammed together in hammocks slung from oak beams.
00:15:00And at meal times, they would eat together at these oak tables.
00:15:08For the crew of the HMS Victory, oak surrounded them.
00:15:11It encased them and it kept them alive against the elements.
00:15:18The oak timbers of the victory withstood the terrifying power of the sea.
00:15:30They managed to cross the Atlantic Ocean in hurricane season.
00:15:34They survived furious battles and innumerable volleys of cannon fire.
00:15:41They saw death and destruction on a colossal scale.
00:15:47And it was an oak hull that cradled Lord Nelson as he bled to death.
00:15:55Each of these spectacular oak planks has borne witness to and survived the many violent and dangerous battles on board
00:16:03HMS Victory.
00:16:04But this wood actually predates the building of the ship by hundreds of years.
00:16:08This wood is a product of medieval acorns that dropped all over Britain.
00:16:13And if you look closely, you can still see the story of their lives etched into the grain.
00:16:20The way oaks live, the battles they face in the natural world,
00:16:26and their incredible adaptations are what makes this species so uniquely useful for building ships.
00:16:38The curved bows of the oak evolved to support the vast canopies of leaves,
00:16:44allow ships to be curved, yet maintain the strength to withstand the full force of the ocean.
00:16:56By planting and cultivating oaks, humans have been able to travel between continents,
00:17:04and spread our species to almost every corner of the planet.
00:17:11Harnessing the strength of this unique organism, we have been able to overcome even the most treacherous of oceans.
00:17:26Back at our tree, it's now late October, and autumn is well underway.
00:17:32Our oak is now getting six hours less sunlight per day than it was in peak summer.
00:17:37And as the sun is the tree's only energy source, it must stock up and store resources for the winter.
00:17:47Crucial to how it does this is the tree's root system,
00:17:51a hidden subterranean world every bit as complex as the world above.
00:17:57I'm extremely keen to investigate how this works, but that's no easy task.
00:18:03Digging up our tree to see its roots would kill it.
00:18:07So to investigate, we are going to excavate the root system of an oak sapling,
00:18:13in its entirety.
00:18:18This is East Malling Research in Kent.
00:18:22For over a hundred years, they have been experimenting with roots and plants to help develop better yields.
00:18:28And they have given us a unique opportunity to get an insight into what's going on beneath the ground.
00:18:36The process begins by digging a metre and a half deep trench.
00:18:42It's only then the real hard work can begin.
00:18:48An oak's root system, even a very young one like this, is incredibly complex and fragile.
00:18:55And that means it can only be excavated by hand.
00:19:01We are trying to ensure that no root, no matter how small, is damaged.
00:19:07And that means the team must be meticulous in their work.
00:19:13It's a painstaking process that will take ten people almost two weeks to complete.
00:19:22But once it's done, we can begin to understand the subterranean world of the oak.
00:19:29Well, this is absolutely incredible. Look at how much soil they've had to remove to expose the root system of
00:19:36this tree.
00:19:36It's only 15 years old.
00:19:38And several tons of earth have had to be shifted.
00:19:42This is something you'll never see in a month of Sundays.
00:19:46And it's something I haven't seen ever before.
00:19:49But just look at the size of this. Look how far they go out.
00:19:52And as you go further and further out, these rootlets get finer and finer and finer,
00:19:56until you're almost, well, you're further out than the tree is tall, virtually.
00:20:04With the roots exposed, we can get a glimpse into their hidden world.
00:20:09Under extreme magnification, we can see these strange threads.
00:20:16They are known as mycorrhizal fungi.
00:20:19They grow all over the oak's roots and help them extract phosphates,
00:20:24a vital nutrient locked inside rocks in the soil.
00:20:31Now, I've just pulled out this little piece of rock here,
00:20:34and I think I can see fungal threads that were actually attached onto this rock.
00:20:41Yes, so there's plant-inaccessible phosphate in that rock.
00:20:45And what the mycorrhizal do is they go inside of the rock and they pull out the phosphate
00:20:50and they can transport that then into the plant and into the root system,
00:20:53whereas the plant wouldn't be able to do that on its own.
00:20:55So the oak tree simply isn't able to access the phosphate in this without the fungi?
00:21:02No. No.
00:21:02Pythia is much smaller and it can penetrate inside of the rock
00:21:05and take the nutrients back into the plant.
00:21:11The tips of the fungi can apply pressure equivalent to the inside of a car tyre.
00:21:17And this means they can physically penetrate parts of the rock to extract nutrients.
00:21:24These are the hidden helpers that allow oaks to get food from the most inaccessible of places.
00:21:33So essentially what we've got here is an oak tree, like any other oak tree,
00:21:36which is totally dependent on a vast army of microscopic fungal filaments,
00:21:44without which it wouldn't survive, and it's a sort of win-win for each of them.
00:21:48They're helping each other.
00:21:49They both require each other to survive.
00:21:51If you stretched out the root system of a mature plant,
00:21:53you would expect it to have about five miles, miles and miles of their root system.
00:21:59However, if you then stretched out the mycorrhiza network,
00:22:03that actually would spread around the entire world.
00:22:06For a single tree?
00:22:08The more I see this system, the more, you know, what I thought of as a complex system,
00:22:17is actually probably a hundred times more complex.
00:22:24To see this root system in its full glory, we are going to take our sapling out of the ground.
00:22:33And put it on display in one of the outbuildings at East Malling.
00:22:51This is what an oak tree in autumn really looks like.
00:22:55At the top, we see leaves are being drained of their nutrients.
00:23:01Below, a vast branching lattice of roots evolved to keep the trees standing
00:23:06and extract water and minerals from the soil.
00:23:13It is here that our oak will store much of its food over the winter months.
00:23:18But laid out like this, the roots are not just beautiful.
00:23:22They also tell us a fascinating story.
00:23:27Now, Peter, to the untrained eye, this just looks like a tangle of roots.
00:23:32But you can tell a story about the tree now.
00:23:35I think we can, because what we can see is a root, as you can see, going down here,
00:23:40before it heads off out in that direction there.
00:23:44And this is almost certainly the root that was inside the acorn.
00:23:49And it's headed on down in this direction. It's grown on down.
00:23:52And then in the place that this was growing, we've got some rock underneath, some sandstone.
00:23:58And this root has hit that rock.
00:24:01And you can see it's branched. It's sent out many branches to try and find a way around the obstacle.
00:24:07And it's sent this one off in that direction.
00:24:11Beneath our oak at Whiteham, the roots, like this sapling, will be a kind of map showing the structure and
00:24:18composition of the earth in which they live.
00:24:23Within the forest, there's a very heterogeneous distribution of nutrients. It's not uniform.
00:24:28And this particular tree has responded to that by producing this plethora of roots, this network of roots in this
00:24:38area, to fully exploit that resource.
00:24:40And presumably once that particular patch of resource here has been used up, it'll just go away.
00:24:46Yes. These roots are ephemeral, they'll die off very quickly, and the plant will invest its resources elsewhere.
00:24:53So it's a highly dynamic system.
00:24:56It's not just fixed and immobile.
00:24:59No. Absolutely not.
00:25:00What we're looking at here is something which is sensing its environment, responding to its environment, and utilising resources in
00:25:11a very dynamic way.
00:25:19At 15 years old, this sapling has developed an amazing system of roots.
00:25:26Our tree at Whiteham will have roots many times thicker, spreading out anywhere up to 30 metres from the trunk.
00:25:35They may seem excessive, but our tree will need them, not just for nutrients, but to keep itself standing.
00:25:46As its last leaves are finally shed, our oak is now fully prepared for the difficult conditions to come.
00:26:17As winter begins, our oak now enters its most perilous season.
00:26:27To survive, it has stripped itself of leaves, revealing an otherworldly beauty.
00:26:38Our tree needs to stay alive, using almost no energy.
00:26:47But in this dormant state, our oak will have to face everything from gale-force winds to sub-zero temperatures.
00:27:02Well, it's now the depths of winter. Our tree is bare, and it's facing some of the harshest conditions it
00:27:07will have to endure all year.
00:27:09At night, the temperatures are going to drop well below freezing, and out of the shelter of the forest, the
00:27:14winds are going to be hitting the top of this tree at full force.
00:27:17To get some idea of what the tree experiences, I'm going to be sleeping, or trying to sleep, 40 feet
00:27:24up there.
00:27:26While our tree looks lifeless in winter, oaks provide a home to species ranging from spiders and wood lice, to
00:27:34bats and owls.
00:27:36They all utilise the great size and stability of the oak to provide shelter.
00:27:44A tree is not just a tree, it's a home.
00:27:51I've always wanted to experience what it might be like to live in an oak tree.
00:27:56And now, I'm finally getting the chance, even if it is just for one night.
00:28:09Getting up to my perch is no mean feat, but it gives me a totally new perspective.
00:28:15Yeah, feels good.
00:28:25Once I'm safely ensconced, it's time to try and get some sleep.
00:28:34At this height, you get a sense of how big a space this really is.
00:28:39For a hibernating bat or nesting owl, our oak would provide everything they need to stay safe over the winter.
00:28:50But for me, sleep is not coming easily.
00:28:55I did hear a couple of noises earlier.
00:28:59Which I thought might have been deer or...
00:29:06I'm sure I heard a fox.
00:29:12Well, it's about 3 o'clock in the morning and it's pretty cool.
00:29:16It's just under 3 degrees.
00:29:18And I'm toasty in my sleeping bag here. I've got these layers of down.
00:29:24And that really insulates me pretty effectively from the cold.
00:29:28And that is working pretty much like the bark of the oak tree, which is an effective insulator.
00:29:34The same principle that is keeping me warm is also keeping our oak and its inhabitants warm.
00:29:41Its thick bark is acting like a blanket.
00:29:46But temperatures in winter can drop below minus 10, and in those conditions, the bark is not enough.
00:29:57Because water expands as it freezes, if our oak were actually to freeze solid in winter, it could cause catastrophic
00:30:05damage.
00:30:07So the oak has an additional strategy.
00:30:10In the lead up to winter, it withdraws some of the fluid from its delicate living cells.
00:30:17It dehydrates itself.
00:30:20What liquid is left contains high concentrations of sugars that act as a kind of antifreeze.
00:30:30It's what allows our oak to survive not just one cold night, but many tens of thousands of them.
00:30:42Well, I came up at night last night in the dark.
00:30:48And it's now apparent just quite how high I am off the ground.
00:30:54Thankfully for me, it was a pretty still night.
00:30:56It's cold, but it's not windy.
00:30:59And the view you get from here is certainly worth it.
00:31:02But it does give me an absolutely unique experience of life in an oak tree.
00:31:14From up here, you really begin to appreciate the scale of our tree.
00:31:18It is a huge habitat.
00:31:22In winter, while our tree might look lifeless, it is actually a vital part of the ecosystem at Whiteham.
00:31:30Our oak is crucial to the survival of countless thousands of insects and other animals over the inhospitable winter months.
00:31:44It's now mid-January and we're going to take a new and very different digital scan of our tree.
00:31:51By imaging the tree without its leaves in these stale conditions,
00:31:55we should be able to get a much more accurate estimate of the weight of our oak's wood.
00:32:01And this will be essential to understanding how the tree changes over the year.
00:32:06Dr Eric Casella from the Forestry Commission is braving the cold for us.
00:32:11And the model he is creating will allow us to see our tree in a totally new way.
00:32:23Eric's scan reveals the sheer complexity of our oak.
00:32:29Using this model, we can work out that our tree is made up of almost ten tons of wood.
00:32:35But the scan also reveals more.
00:32:38Its branches are distinctly clustered to one side of the tree.
00:32:43Our oak has directed the growth of its branches away from the sides shaded by the forest and towards the
00:32:49area that receives most sunlight.
00:32:52It's uniquely optimized its shape to suit its position.
00:32:57But this phenomenon is not just above ground.
00:33:00An oak's root system adapts to help them stay standing in winter.
00:33:05To see how this works, I want to try something that has never been done before.
00:33:10I want to simulate the effects of gale force winds on an oak.
00:33:17This is a forestry commissioned research site just outside Edinburgh.
00:33:21And here, they're doing pioneering work, examining the strength and stability of many different tree species.
00:33:28They have allowed me in for the afternoon to come and watch one of their experiments.
00:33:34Today, for the first time, they're going to study how an oak tree behaves during a storm.
00:33:41Some people might be a little bit shocked that you're just about to pull down a perfectly healthy oak tree.
00:33:47What's the reason for doing it?
00:33:49Well, one of the reasons that we do this is to assess the stability of trees and forests.
00:33:55And without doing this, we don't know what happens when a storm hits.
00:33:58You're trying to simulate the sorts of forces that that tree would experience in a high wind.
00:34:04Exactly.
00:34:05Before we pull it, the tree must be rigged with sensors to monitor exactly how it behaves under stress.
00:34:12Once everything is set, it's time to get back to a safe distance and begin the pull.
00:34:31Keep moving.
00:34:33Keep moving.
00:34:34Keep moving.enser
00:34:35.inctions.
00:34:39It's definitely going.
00:34:55Beautiful.
00:35:01With the tree down, Paul and his team can now analyse the results.
00:35:07At what angle did the tree suddenly become sufficiently tilted over that it fell on its
00:35:16own?
00:35:16In this case it was only six degrees.
00:35:19That's nothing.
00:35:20That's like that.
00:35:21That's correct, yeah.
00:35:23So that tree actually, you know, it's got very shallow roots, it's not very big is it?
00:35:29No, that's exactly what it is.
00:35:31You can see when we looked at the roots that it was very shallow.
00:35:35While at first glance it may seem this oak came down quite easily, it would have taken
00:35:39a force 10 storm to produce the same effect as Paul's winch.
00:35:45That size of storm can produce 12 metre waves at sea and has gusts of wind anywhere up to
00:35:5090 miles an hour.
00:35:53This oak was in fact amazingly stable given its relatively shallow roots.
00:35:59It's likely our oak has grown much deeper roots and with its huge spread of branches it is
00:36:05able to dissipate the force of the winds much more effectively.
00:36:10It means that our tree can withstand much harsher conditions.
00:36:15That a large heavy structure like our oak can remain standing over 400 winters is a remarkable
00:36:22feat of evolutionary engineering.
00:36:25And much of what has made it so successful at surviving the cold and the storms of winter
00:36:31has also made it useful to us.
00:36:40For thousands of years oak has been an essential building material.
00:36:46By slicing and shaping trunks of oak into regular lengths we are able to build all manner of
00:36:53shelters to protect us from the elements.
00:37:02In the harsh winter months oak timbered houses have kept us safe for centuries.
00:37:08And thanks to the durability of the wood many of these incredibly old buildings still endure
00:37:14today.
00:37:16But there is perhaps one building above any other that showcases the extraordinary properties
00:37:22of oak timbers and just what they can help us create.
00:37:30Built in the 13th century it remains one of the most imposing and impressive structures in
00:37:36the British Isles.
00:37:38And at its heart is oak.
00:37:57This is Salisbury Cathedral.
00:37:59It's one of the masterpieces of British medieval architecture.
00:38:03Looking at its size and scale it's hard to believe this building was created almost 800 years ago.
00:38:10And throughout its incredible structure everywhere you look oak has been put to use.
00:38:19During its construction an incredible 2,641 tonnes of oak were employed to help build the cathedral.
00:38:35But it's not until you ascend above the vaulted plaster ceilings that you can really understand
00:38:41how important this single species of tree has been.
00:38:58This building has within it whole forests reimagined and remoulded by human hands.
00:39:17Now these oak beams have been here for a very long time.
00:39:21In fact these are among the oldest of the oak beams here.
00:39:24Yeah, the area we're in now is 13th century timber.
00:39:28It's been tested and it was felled in 12 spring of 1222.
00:39:39The roof here can be dated so precisely thanks to patterns in the wood.
00:39:46As an oak grows it makes large amounts of new tissue in the spring followed by a much smaller
00:39:52amount of denser wood later in the year.
00:39:56This rapid then slow growth gives the appearance of rings.
00:40:01If the summer weather is good a tree will grow a much wider ring and that gives us a tantalising
00:40:08snapshot of the past and its climate.
00:40:12By looking at similar patterns across many different samples it's possible to date pieces
00:40:17of oak with extreme precision.
00:40:21It's even possible to tell where an individual oak tree was growing.
00:40:26And it turns out to build this amazing roof the local craftsmen used oak from as far afield as Ireland.
00:40:34These two don't look quite the same to me.
00:40:37No, if you look at the rings closely, this is Irish oak.
00:40:42The tree rings are really tight together because the summer and the winter almost blend into one another.
00:40:50English oak, they have hotter summers so they have a better growth rate during the summer.
00:40:55It makes it stronger and it's also slightly lighter as well.
00:40:58Which when you're putting thousands of tons of oak into a roof structure, you know, it all adds up.
00:41:06It all adds up, yeah.
00:41:09With Salisbury's spectacular roof completed, its builders decided to add one extraordinary feature.
00:41:18A monumental spire that must have filled the medieval population in the surrounding area with absolute awe.
00:41:28Today, it still remains the largest spire in the UK.
00:41:33And inside is an incredible lattice of oak timbers.
00:41:40I tell you, if you didn't, if you didn't like heights, this would be,
00:41:46this would be not much fun for somebody.
00:41:48This is quite an amazing feat of engineering, really.
00:41:52And it was essentially an afterthought after the cathedral was built.
00:41:56And they've had to do this ingenious framework to help them build it.
00:42:01Yeah, a thousand people were working on it.
00:42:03They were doing it to get closer to God, if you like.
00:42:05So it was their vocation, their way of life, to be closer to heaven.
00:42:11But you just look up and marvel and you almost think it's divine intervention, isn't it, really?
00:42:16It is probably one of the most amazing structures I've ever seen.
00:42:36Well, you do get an amazing sense of the countryside from up here.
00:42:40But don't forget, it's the oak forests growing down there.
00:42:43The fact that they can withstand all that the weather has to throw at them,
00:42:48even in the harshest of winter.
00:42:49And the strength and durability and resilience of the wood that they gave,
00:42:54that made structures like this possible at all.
00:43:01Oak is an incredible building material.
00:43:03But even today, we have yet to come anywhere close to creating structures
00:43:08with the economy and beauty of the oak tree in its natural form.
00:43:21As the winter deepens and temperatures drop down below freezing,
00:43:26our oak structure will really be put to the test.
00:43:29I want to find out exactly how healthy our oak is
00:43:33and how many more winters like this it might be able to endure.
00:43:41Thanks to some ingenious new technology, we now have the power to look inside it and find out.
00:43:48This is very similar to the MRI scanner that we use on the body.
00:43:52So it takes slices through the body, we take slices through the tree,
00:43:55and we're just trying to determine whether the wood is sound or not.
00:44:00As electrical currents are passed through the tree,
00:44:03a map is created that will reveal the internal structure of our oak.
00:44:07Well, there's the image. What does that show us?
00:44:11Well, what it's showing us is we've got wet and dry areas basically, George.
00:44:15The dry areas are in red, some of them around the outside of the stem.
00:44:19The bulk of the stem in the middle is blue, but there are breaks in that,
00:44:22and that suggests to us that there's something wrong with the inside of the stem.
00:44:26It's not a natural picture. Clearly something has happened and we need to investigate that further.
00:44:32This tiny gap between the roots of our oak may look unremarkable, but inside is a hidden world.
00:44:39Let's get this into position so you can see.
00:44:42Oh, that's quite a big hole, isn't it?
00:44:44Ooh.
00:44:45And we can see all that decayed wood.
00:44:47So we've got a very, very large cavity where the heartwood is missing,
00:44:52and we can see fingers of wood hanging down where the fungus has rotted out the wood between it.
00:44:57We call it the Eiffel Tower fungus. It really only affects the lower part of the stem and leaves the
00:45:02tree
00:45:02effectively standing on its buttresses like this buttress here, a bit like the Eiffel Tower on its four legs.
00:45:08Hence the name.
00:45:09We've got multiple legs, hence the name.
00:45:11Now, I mean, even though that is quite a big hole, it's clearly not having a hugely harmful effect of
00:45:17the tree.
00:45:18It's still here. It's still growing.
00:45:20Absolutely. It's still got these feet in the ground, if you like, and still draw up nutrients and water,
00:45:25and give it a firm footing in the ground, even though the heart's gone,
00:45:29and it could still be there in another 500 years.
00:45:34It's likely our oak will still be standing here, alive and growing in the landscape of the 26th century.
00:45:44But after this vast span of time has passed, the fungus eating away at our trees inside
00:45:50and the age of its wood will mean it looks quite different.
00:45:56Scattered across the UK are a select few oaks that have survived over a thousand years,
00:46:03and they give us clues about our tree's ultimate fate.
00:46:15This is the Bowthorpe Oak in Lincolnshire, and over the last one thousand years,
00:46:21its insides have been almost entirely hollowed out by fungus.
00:46:35Each valley, ridge, and peak in its wood tells the story of the battles this tree has faced.
00:46:52It's bark looks like the surface of an alien world.
00:47:04Sculpted by huge passages of time.
00:47:10Sculpted by huge passages of time.
00:47:42The Bowthorpe Oak is a window into our tree's distant future.
00:47:47The Bowthorpe Oak is a window into our tree's distant future.
00:47:50But for now, our tree is thriving.
00:47:53It has endured everything the winter has thrown at it and is ready and waiting to once again come to
00:48:00life.
00:48:15As the temperature warms and the forest is bathed in sunlight,
00:48:19the countless plants and animals in Wighton Woods come to life.
00:48:26Once again, the forest is reborn with colour, movement, and life.
00:48:38And for our oak, this will be the season of most dramatic growth.
00:48:44After many months in a state of suspended animation, our oak is beginning to come to life.
00:48:50The buds are finally starting to burst, and our tree is about to undergo one of the most dramatic changes
00:48:57of the year.
00:48:57In the next few weeks, this oak is going to have an epic growth spurt.
00:49:06To capture this transformation, we are setting up two specially designed cameras.
00:49:12Bolted to the spot, they will take over 100 pictures each day,
00:49:16and allow us to compress this spectacular event into a timescale we can appreciate.
00:49:26Just like our tree, the cameras will be powered by the sun, and will capture images continuously for the next
00:49:32six months.
00:49:34With everything set, the cameras are started.
00:49:45As winter ends and spring begins, over 700,000 individual leaves emerge across our oak.
00:49:58It's a truly astonishing change.
00:50:16This remarkable transformation needs huge amounts of water.
00:50:21Hidden from the naked eye, at its peak, our tree will be pumping 70 kilograms of water each hour out
00:50:28of the ground.
00:50:31By looking at the oak wood just beneath the bark with a microscope, we can see how this huge quantity
00:50:36of water gets moved around the tree.
00:50:40These intricate pipes are known as the xylem vessels, and they run through a layer known as the cambium,
00:50:46that carries water upwards from the roots to the leaves.
00:50:52And thanks to some ingenious technology, we can now measure exactly how much fluid is moving through them.
00:51:01With the help of Dr Lucy Rowland, I'm going to set up an experiment that I hope will reveal
00:51:06exactly how much water our tree is taking up, and how this changes over the spring.
00:51:13This is a sap flow monitor, and as water travels up the xylem tissue, these probes heat it up.
00:51:20By measuring how quickly this heat is carried away, the device can calculate how much water is flowing
00:51:26through the trunk of the tree. Over 24 hours of measurements, we see our tree's water consumption
00:51:33varies dramatically. This is at night, when we don't have sap flowing up through the tree.
00:51:39And this peak here, this is lunchtime-ish yesterday, when we have maximum flow up through the stem of the
00:51:46tree.
00:51:46And you can see here that we've got about 10 kilograms of water per hour yesterday lunchtime,
00:51:54going up through the tree. And that will increase as the leaf area of the tree increases.
00:52:00Yeah, so the more leaves that come out on this oak over the next few weeks, the bigger that this
00:52:07peak is going to be.
00:52:09As we move through the next two weeks of spring, our tree begins to consume ever more water in the
00:52:15middle of the day.
00:52:18It reaches a peak of over 60 kilograms of water an hour as more and more leaves emerge.
00:52:31But leaves are not all our tree is now producing. It's now late April and for a precious few weeks,
00:52:38our oak grows these strange new structures. Their role is to ensure the future of our tree
00:52:46and the continuing success of the oak.
00:52:50These fragile little objects are known as catkins, and they are oak's male flower.
00:52:56And it's the appearance of these every spring that signals the start of the oak's reproductive cycle.
00:53:01And if you look carefully inside each of these little blobs, you'll find it's completely packed with grains of pollen.
00:53:10But these pollen grains are only half the story.
00:53:14Our oak will also produce a female flower,
00:53:17but not until later in the spring.
00:53:20It means that these pollen grains will need to find a female oak flower on another tree
00:53:24if they want to pollinate, and that means taking to the skies.
00:53:35In spring, an oak tree like ours can release up to two billion individual particles of pollen.
00:53:41And inside each one of these tiny grains is the unique DNA of our tree.
00:53:47Blown around by the wind, they can spread for miles, but their mission is simple.
00:53:52Each grain is seeking a chance encounter with a female flower on one of the other 5,000 oak trees
00:53:58in the surrounding woods.
00:54:03Filling the air above the forest, billions of our oak's individual pollen grains
00:54:08are scattered by the spring breeze.
00:54:17Up close, we can see how complex this tiny vessel really is.
00:54:22A thick warty shell protects the delicate genetic cargo inside,
00:54:27as gusts of wind carry it for miles.
00:54:34This is the target of our oak's pollen grains.
00:54:38A female oak flower.
00:54:44If the pollen is lucky enough to land here, it will fertilise the flower.
00:54:48And over the next few months, the female oak flower will combine its genetic material
00:54:53with the pollen to create a tiny acorn, a descendant of our oak.
00:55:08The yearly act of pollination is crucial for the long-term future of the oak.
00:55:13But at Whiteham, they have been using pollen to open up a unique window into its past.
00:55:19This is Marley Fen.
00:55:21It's an area of Whiteham Woods that's remained largely unchanged for thousands of years.
00:55:26And over that time, as plants and trees reproduce every spring, the air is filled with trillions and
00:55:32trillions of pollen grains that eventually end up in this peat here.
00:55:37As pollen settles on the surface of the fen, plants, leaves and other biological matter
00:55:43gradually build up on top of it.
00:55:46Over time, layer upon layer of pollen becomes preserved within the soil.
00:55:52Inside this somewhat unremarkable looking mud, an incredible story has been preserved,
00:55:58one that records in detail the ebb and flow of various trees and plants in the area for the last
00:56:0412,000 years.
00:56:05But to uncover the story hidden in here, you have to dig down.
00:56:11And that's what Dr Helen Walkington and her team have been doing for the last 10 years.
00:56:18They use a long metal tube to extract thin cylinders of peat from the fen.
00:56:27This four-metre-long core can tell scientists how the landscape and vegetation at Whiteham Woods
00:56:33has changed since the end of the last ice age.
00:56:42This soil from four metres down was on the surface 12,000 years ago and shows Britain then was a
00:56:49cold and barren place.
00:56:53So we've got here clay-rich material with lots of iron and fragments of rock.
00:56:59So I don't know if you can see here, but there are rock fragments within it.
00:57:04So it tells us that there was lots of erosion in this landscape.
00:57:07And that's how we know that there wasn't much vegetation at the time.
00:57:11Without plant roots to hold the soil in place, the landscape of Britain after the last ice age was prone
00:57:18to rapid changes.
00:57:20But as we move along the core, more and more pollen begins appearing as plants of all kinds take hold.
00:57:27As the climate warmed, it meant oak was able to move north and 9,000 years ago its pollen appeared
00:57:35for the first time at Whiteham.
00:57:38This material would represent organic matter that would have been moved into Marley Fen 9,000 years ago.
00:57:46And at the same time, oak pollen would be blowing around in the atmosphere and would settle out on the
00:57:52surface.
00:57:53And gradually all the material and the rest of the core would be on top and pushed down.
00:57:57I find it incredible that I can actually put my finger on that piece of core and touch the exact
00:58:03part of the history of Whiteham where oaks came in.
00:58:079,000 years ago.
00:58:099,000 years ago. I can actually physically connect with that.
00:58:12Yeah.
00:58:12And what are humans doing at this time?
00:58:15At this time, we don't have humans at this point.
00:58:20This is it. This is pristine.
00:58:22Once the humans do come into the landscape, things start changing very quickly.
00:58:28Moving through the core to nearly 2,000 years ago, cereal grains begin to appear at Whiteham and this signals
00:58:35a new type of human activity.
00:58:39Cereal grains are brought in by the Romans and they need to completely clear the landscape to make space for
00:58:45fields to cultivate them.
00:58:47The cereals, we don't know the exact type of cereal that they were growing because the shape of the pollen
00:58:52grains doesn't unlock that for us like it does for the trees, which we can get down to the species
00:58:57level.
00:58:57But certainly, yeah, the Romans would be using this landscape to grow food and then as we progress up the
00:59:05core, we find that oak becomes less dominant at this height.
00:59:11It's still present, but it becomes less dominant and that's because humans have set about clearing these landscapes on a
00:59:19much, much greater scale.
00:59:20The oak tree that we're filming in Whiteham Woods is going to be growing somewhere about here?
00:59:27Yeah, it was probably an acorn around 0.7 meters, something like that.
00:59:33And so over that, that represents the period of time that your oak tree's been growing.
00:59:38But at least it shows that things change over time and there have been huge, huge changes in 12,000
00:59:47years, which is a very short piece of Earth's history.
00:59:49Absolutely. And in 12,000 years, those changes have been natural and human induced and there's a kind of interplay
00:59:58of those at this site.
00:59:59And I'm sure that in the next 1,000 years, that will be the case as well.
01:00:05The oak's pollen offers us a vivid glimpse into challenges trees face over vast spans of time.
01:00:12But right now, our tree is gearing up to face a much more imminent danger.
01:00:26It's now late May and our tree is in full leaf.
01:00:31The oak boughs visibly droop with the weight of the new material they have to support.
01:00:37But this abundance of young, soft leaves are extremely vulnerable.
01:00:42A great threat is now emerging and our tree must react quickly if it wants to survive.
01:00:49This is the larva of the winter moth.
01:00:51It may not look very much, but this is one of the oak's most fearsome enemies.
01:00:56This little chap will eat an incredible amount of food to become adult.
01:01:00In fact, it will eat up to 27,000 times its own weight in young oak leaves.
01:01:06And right now, there are countless thousands of these caterpillars infesting our tree.
01:01:11But our oak isn't powerless in the face of this attack.
01:01:17After the oak's new leaves first emerge, for a short while, the winter moth caterpillars, amongst others,
01:01:24will gorge themselves.
01:01:27Unprotected from these attackers, our oak would struggle to survive the summer.
01:01:33But incredibly, our tree is actually able to recognise exactly what's happening to it and respond.
01:01:46It's a very interesting story.
01:01:46Professor Sue Hartley has spent much of her career looking at the ways plants defend themselves
01:01:51against insect attacks and was one of the first to recognise just how sophisticated trees like our oak
01:01:58really are.
01:02:00How does an oak tree know it's being attacked?
01:02:03Well, that's really interesting.
01:02:05This is a winter moth and it's about to tuck in and you can see that when they eat
01:02:10the leaf, they chew the edge and they're really messy eaters.
01:02:16Saliva's going all over the leaf, there's lots of goo on the leaf surface.
01:02:20And within that saliva, there are chemicals that the oak tree can recognise.
01:02:26While we might see or hear approaching danger, the oak senses it chemically.
01:02:32It's hard to appreciate as we have no analogous sense, but it's an incredibly fine-tuned and refined system.
01:02:41This chemical signalling is really sophisticated, so our oak tree can tell whether it's a caterpillar or whether
01:02:49it's a different kind of herbivore like a sap sucker, an aphid that feeds in a different way.
01:02:55And it's even better than that. The oak tree can tell the difference between big caterpillars and
01:03:01small caterpillars. The age of the caterpillar can be detected.
01:03:04That is amazing. Once our tree has sensed it's being attacked in one place, it's actually able
01:03:10to signal to itself to warn other parts of the attack.
01:03:15It produces something called wound hormones and those hormones move all around the plant in the sap
01:03:21system and that tells the plant to turn on its defences in other parts of the tree. And they
01:03:27also cause airborne signals to be released that also travel all around the tree. So the defences are
01:03:33ready all over the place. So if one branch, if that little branch there was suddenly attacked
01:03:38by lots of caterpillars, the tree would know and it would protect all the rest of itself.
01:03:43It would start to, yes. It talks to itself and there's a sort of chattering goes on across
01:03:49the whole canopy. Once our tree knows it's being attacked, it begins to produce poisons
01:03:55that will stop its attackers in their tracks. The main defences in oak are chemicals called
01:04:03phenolics and tannins. Now that's what you have in your tea cup. I mean that's what gives tea
01:04:08a taste. Tea contains a lot of tannin and it's tannin that produces that bitter flavour in tea
01:04:15because the tannin binds with protein in your mouth, your saliva and gives it that sort of bitter taste.
01:04:23And that's exactly what happens when the insects try and feed. They find that the chemicals in the
01:04:29oak leaves will bind to the proteins in their digestive system and stop them growing so well.
01:04:34So it may look like the tree is just a big green heap of food but eating it's not that
01:04:40easy.
01:04:41It's a real challenge to eat plants. They're full of defences and they're very clever and they're able
01:04:48to detect the things that attack them. They've had millions of years to evolve to do that
01:04:52and they've got a very sophisticated armoury.
01:05:01After keeping the insect hordes of early spring at bay, our tree can continue its rapid growth.
01:05:08But now a new danger is emerging. An outlandish group of insects that have hijacked our oak's growth
01:05:16for their own ends. They are without doubt the strangest and most sophisticated foe our oak will face.
01:05:32This is a gall wasp. By laying its egg in a female oak flower it causes a profound change in
01:05:43the way our tree grows.
01:05:47It induces a kind of tumour known as a gall to grow in place of an acorn.
01:05:57Inside the gall a grub develops feeding on the nutritious tissues within while being given shelter from enemies.
01:06:07This bizarre structure is the perfect nursery.
01:06:17This particular structure is known as a nopper gall and it is the product of just a single species of
01:06:23wasp.
01:06:24These wasps always produce this type of gall.
01:06:28But there are many other species of gall wasp and they can induce very different shaped growths.
01:06:38The remarkable thing about galls is their sheer diversity.
01:06:42There are several hundred species of gall wasp and each one makes a gall of a specific shape and size.
01:06:49But galls are not just random overgrowth of the oak. The gall wasps are actually using chemical signals
01:06:55in very subtle ways to hijack the developmental machinery of the oak at an early stage.
01:07:03The exact way each species of wasp manages to produce such individual and unique galls is still somewhat of a
01:07:11mystery.
01:07:13But it seems they may actually be altering the oak's DNA.
01:07:18Genetically engineering it to grow a home for their young.
01:07:23The myriad of different types of structures these wasps create for their offspring is simply staggering.
01:07:31But of all the weird and wonderful types of oak gall there's one that has a strange connection with the
01:07:37human race.
01:07:39One type of oak gall has shaped our history.
01:07:43That's because for a thousand years it was the source of a special kind of ink with which nearly all
01:07:50our historical documents were written.
01:07:55Crushed, mixed with water, iron sulphate and gum arabic, the humble home of the Andracus cholerae wasp is transformed into
01:08:06a cheap and extremely long-lasting ink.
01:08:10This is the National Archives at Kew.
01:08:14In the vaults of this building are housed over a thousand years of British history in the form of millions
01:08:20upon millions of documents.
01:08:24Stored in these unassuming boxes is our past and a huge amount of it is recorded in gall ink.
01:08:32So almost any document of any importance had to be written or was written using ink made from oak gall.
01:08:42That's right it's the most important ink that we have in western history.
01:08:46What made it so good as an ink?
01:08:49It's an indelible ink so it's very hard to remove and you can see in some of these documents here.
01:08:58These are from the trial of Guy Fawkes.
01:09:01No.
01:09:02Yes, we're very lucky to have them.
01:09:04The actual records?
01:09:04Yep, these are the actual records of Guy Fawkes's trial and here you can see
01:09:10a nice example of how indelible the ink is.
01:09:15So here the scribe has made a mistake and to correct his error he's actually had to scrape
01:09:22the surface of the parchment off, remove the ink from the surface and then rewrite over it.
01:09:29You can see this dark patch here and the difference in the colour because this part of the ink was
01:09:34put on much later.
01:09:35This is a really good illustration. These kinds of legal documents had to be kept in ink that was going
01:09:42to last,
01:09:43had to be written in ink that was going to be lasting. So they're written on material parchment
01:09:48that's more durable and they're written with an ink that is not going to just vanish before your eyes.
01:09:54But oak gall ink wasn't just used for official documents. Everyone from poets, musicians and mathematicians
01:10:02to fine artists used this ink to record their thoughts, feelings and ideas.
01:10:09The whole of Western civilisation between, from about the end of the Roman period to the 19th century,
01:10:17our most important texts are in iron gall ink.
01:10:20It seems just a bizarre twist of fate that all of this, and there are how many thousands of documents
01:10:28here
01:10:28which are written in this ink, began because a tiny wasp laid an egg in an oak bud that grew
01:10:36into a gall
01:10:38and that provided the basis for essentially our recorded history.
01:10:42That's right. What is surrounding us is just a small fragment of all the documents
01:10:48that survive from those 1400 years of history.
01:10:54From wasp to gall to human hands, this little quirk of evolution has shaped human history.
01:11:10This incredible ink brought us the Magna Carta and the American Declaration of Independence.
01:11:18It has brought us the music of Mozart and Bach and the drawings of Rembrandt and Leonardo da Vinci.
01:11:30Thanks to gall ink, we have Isaac Newton's theories and the letters of Charles Darwin.
01:11:39The Magna Carta and the American Declaration of Independence.
01:11:40The Magna Carta has enabled us to record our past, to express our most profound ideas,
01:11:45and to share our deepest emotions.
01:11:48The Magna Carta and the Magna Carta
01:12:05It has brought out its leaves, it has spread its pollen for miles around,
01:12:09and it has repaired the damage sustained over winter.
01:12:13Now, as the insect populations grow ever larger,
01:12:16this mighty organism is finally ready to face its most challenging season.
01:12:38It's now June, and under the intense sunlight, trees and plants are working at full capacity.
01:12:50For the countless life forms of the forest, it's a time of plenty.
01:12:56And at the centre of this frenetic activity is our oak.
01:13:06There are hundreds of insects that depend on the oak for sustenance,
01:13:11but I want to see the insects us humans don't normally come across.
01:13:17The ones that live high up in the oak's canopy.
01:13:26Well, it's now the height of summer, and the tree is in full leaf.
01:13:31There's even some acorns beginning to swell.
01:13:34This is just an enormous cathedral-like space.
01:13:41What's very frustrating when you're on the ground is that you know there are lots of fantastic insects and animals,
01:13:51but you can't reach them.
01:13:54So the only way to get to them is to climb.
01:14:06I can just find a nice place to stand.
01:14:13Wow. There we are.
01:14:22Wow.
01:14:27This is a very privileged view of an oak tree, and one that only an insect would have.
01:14:36There are some insects up here that you'll never see from the ground.
01:14:46I can just shake the foliage, try and get some insects in the bag.
01:14:58I'll bet there's lots of good stuff in here.
01:15:01Now, the next bit of kit is the pooter.
01:15:05That allows me to suck insects out of the net without handling them,
01:15:11because lots of these things are very small.
01:15:19So, let's see what we've got.
01:15:21High up in our tree, there is a wealth of life.
01:15:24This is where the good stuff will be.
01:15:27Mmm.
01:15:33But to get a sense of its diversity and the unique adaptations of creatures up here,
01:15:38we have to take a closer look.
01:15:41And we can do that under the microscope.
01:15:45Now, I've got quite a few insects in here.
01:15:48I think we'll just empty them in there and just hope for the best.
01:15:50Great.
01:15:51I'll just whack them in.
01:15:52Sure it will be fun.
01:15:53Oh, big earwig there. Look at that.
01:15:57What is absolutely amazing with this machine is the quality of that image is just breathtaking.
01:16:06Well, that is the head end of a cricket.
01:16:10And she's having a preen here.
01:16:12The very interesting thing about these insects is that they have their ears
01:16:15on the front leg, on the knees of the front leg.
01:16:18And there we go.
01:16:19You'll see a little opening there.
01:16:20And that is the opening of her hearing organs, which are here and here.
01:16:25And by having their ears on their front legs quite far apart,
01:16:29you're able to triangulate and know exactly where that sound is from.
01:16:34Now, let's see if we can see anything else here.
01:16:36There are absolutely minute things in here.
01:16:40Tiny little thing, a mite, absolutely minute.
01:16:44And there are probably millions, tens of millions of these up a tree.
01:16:49That animal is tinier than the claw on the hind foot of the cricket.
01:16:56This spectacular variety of insects are all at their most active in summer.
01:17:01And many of them are specially adapted to eat our oak's leaves.
01:17:05This is a plant hopper, and it's able to suck out sugary sap from individual plant cells.
01:17:12When these sap suckers attack on mass, it can be devastating to the delicate leaves of our tree.
01:17:19There are many, many different insect species who call our tree home.
01:17:23But there are a select few who have a special relationship.
01:17:28Species that have evolved to specifically take advantage of the oak.
01:17:34This is one of our tree's infant acorns, finally beginning to emerge.
01:17:40It's a beautiful, intricate structure.
01:17:46But something here is not right.
01:17:49This strange black hole is a sign this acorn has been tampered with.
01:17:58The culprit is one of the most highly specialised and bizarre species on the oak.
01:18:12The acorn weevil.
01:18:20Look at that!
01:18:23Is that not just the most beautiful thing?
01:18:27This is an animal that's evolved specifically with oak trees.
01:18:31And it lays its eggs in acorns.
01:18:33And it's got this enormously long beak that comes out of its head.
01:18:38At the end of that beak are a pair of tiny jaws.
01:18:41And it drills deep into acorns to lay its egg in the acorn.
01:18:47And she has these peculiar antennae, which are elbowed, hinged.
01:18:53And as she drills into the acorns, she can fold them back along the side of the head.
01:19:00Our weevil also has highly specialised bi-lobed feet.
01:19:05With which it's able to grip onto the smooth surface of the oak's acorns.
01:19:14Weevil to see them this close brings you into their world.
01:19:19You can understand the mechanics of what they have to do, how they have to live.
01:19:34It doesn't get any better than this, really.
01:19:36That is just evolution at its most wonderful.
01:19:44The acorn weevil is just one of many insects up our tree.
01:19:48On one single branch there's a beautiful and deadly lacewing.
01:19:52Other insect predators such as a damsel bug and a comb-footed spider.
01:19:58And the tussock moth caterpillar who can feast on our oak's leaves.
01:20:03All of these insects have found ingenious ways to use the oak for their own ends
01:20:08and extract food from it in some way or other.
01:20:13And it's not just insects.
01:20:16Us humans also consume oak.
01:20:18In fact, we can drink it.
01:20:21To discover more about this, I'm going to the land of my forefathers.
01:20:28Scotland.
01:20:31This is the Scotch whisky experience in Edinburgh.
01:20:34With 3,384 different bottles, it's the world's largest whisky collection.
01:20:41To be legally called a Scotch whisky, the alcohol must be stored in oak barrels for at least three years.
01:20:48Whisky is, in essence, oak-flavoured alcohol.
01:20:53Does the growth of the oak tree affect what the whisky will eventually be?
01:20:59Yes, it absolutely can do.
01:21:01Generally, what happens in Quercus species is the tree lays down material in two distinct parts of the year.
01:21:08In springtime, it lays down early wood, which is like a sponge, very porous.
01:21:13The rest of the year, late wood, which is hard and dense.
01:21:18The early wood is more porous or spongy, therefore it can give forth more flavour.
01:21:23So if you're really fussy about the type of barrel you want to use, you will go for so-called
01:21:29tight-grained oak,
01:21:30typically 12 to 16 growth rings per inch if we're going to get very specific about it.
01:21:36By treating oak barrels in different ways, by charring them and seasoning them with other wine and spirits,
01:21:43it's possible to release multiple chemical compounds from the oak, leading to an incredible diversity of whisky flavours.
01:21:51So what we've got is actually a very complicated system.
01:21:57All these compounds which give flavour to the whisky, how many different flavourings are there, would you think?
01:22:05I would say that there's probably between 50 and 100 different compounds we can identify that have come out of
01:22:12the oak wood that can influence the character and flavour of the whisky.
01:22:16So when you drink your mature whisky, all these lovely buttery flavours, the soft texture in the palate,
01:22:23the sweetness, the vanilla, the coconut, the almond, all of these flavours are drawn directly from the good quality oak
01:22:31wood.
01:22:32The multitude of flavours that whiskies possess are testament to the complexity of the oak's wood.
01:22:47From weevil to human, there are many hundreds of species that eat or consume the oak in some way.
01:22:54But what does our tree eat? Where does it get its energy from?
01:23:00The answer is, of course, the sun.
01:23:03And at the height of summer, this process, famously known as photosynthesis, is at its peak.
01:23:14To see how the tree does this, we need to look at its leaves under the microscope.
01:23:24These strange openings are called stomata and they suck carbon dioxide from the atmosphere into the leaves.
01:23:34Then, powered by sunlight, this carbon dioxide is combined with water and turned into sugars that our tree feeds on.
01:23:44But as they photosynthesise, our oak's leaves perform one final magic trick.
01:23:52Out of the many billions of stomata, pours oxygen.
01:23:58It is perhaps the single most important process in the natural world.
01:24:09At the height of summer, our oak, its magnificent structure and its hundreds of thousands of leaves,
01:24:15are able to bask in the sunlight and convert it into food.
01:24:20In the process, it pumps out the oxygen that we all rely on to stay alive.
01:24:27In this single act, our oak is performing a feat that we have yet to match.
01:24:40As August begins, it's now been a year since we made the first digital model of our tree.
01:24:47Thanks to the detailed measurements we've taken over the year, and the weather data from Whiten Woods,
01:24:53it's now possible to make estimates that reveal the ways our tree has changed.
01:25:00Despite its age, our tree has grown.
01:25:04Over the last 12 months, it has been extracting carbon dioxide from the atmosphere through its leaves,
01:25:09and some of this has been refined into carbon and forged into new wood.
01:25:17While our oak's great size and age means that new growth is extremely thinly spread,
01:25:23it has increased in size. In fact, our tree has created 230 kilograms of new wood.
01:25:31This much material has literally been plucked from thin air.
01:25:36To help it grow and photosynthesize, our tree has had to consume huge quantities of water.
01:25:43Thanks to our sap flow data, we can see that over the 71 days we recorded it,
01:25:49the tree drank an incredible 58,822 litres of water.
01:25:55But our oak tree hasn't just taken from the environment around it. As it photosynthesizes,
01:26:01its leaves produce oxygen. Since we've been filming, our tree has released an incredible
01:26:08234,000 litres of oxygen into the atmosphere. And that much oxygen is enough to keep me alive for a
01:26:15whole year.
01:26:21By spending a year looking at this one tree, we have been able to see just how dynamic and complex
01:26:28this organism really is.
01:26:31We've seen how it can create 700,000 leaves and keep them safe. We've seen how it can withstand the
01:26:39harsh winter conditions.
01:26:41And we've seen how our tree sits at the centre of a vast interconnected web of life.
01:26:48In the face of everything thrown at it, the wind, the rain, freezing temperatures and the constant attack
01:26:55by insects and fungi, our tree has thrived. In the process, it's provided a home and a source of food
01:27:02for millions of individual organisms. It's what makes this incredible species such an important part
01:27:09of the British countryside. The oak's endurance and longevity have woven it into the lives of the
01:27:21thousands of creatures that rely on it.
01:27:32And that includes us. This colossus of the British Isles has permeated our culture.
01:27:45Oaks have shielded us, protected us from danger.
01:27:50They have allowed us to explore the seas. They have brought us pleasure.
01:27:58They have helped us express our most profound ideas.
01:28:04Oaks have borne witness to our deepest sorrows and our most joyful moments.
01:28:15This plant, perhaps more than any other, has become part of us.
01:28:34Coming up next tonight here on BBC Four, could the detectorists be about to uncover a murder?
01:28:39Comedy in just a moment.
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