Hello, my name's Lindsay Turnbull and I'm an associate professor in the Department of Plant Sciences at the University of Oxford,
and we're right in the middle of this very serious corona virus crisis right now.
And my students are all stuck at home and we want to keep them in touch with biology and keep in touch with us.
And so we're going to make a new series of videos and they're going to be called back garden biology.
Hello, welcome to this episode of Background Biology.
It's a beautiful, sunny day, Sunday in January, but the sun is shining on us, so that's keeping us all going.
So if you're at home and you're enjoying that sun as well. I thought this episode, I'd come back out and take another look at trees.
I did a first episode bout that went to white and woods and saw lots of trees growing in a woodland setting.
Perhaps he realised in my local part, there are lots of other trees and more things to see and to talk about.
And I really love the trees in winter.
One of the things that really cheer me up, I love the silhouettes of the trees, having a look at them, trying to guess what they all are.
So I'm standing by a black poplar here. It's got very deeply riven bark, which will take a closer look at the moment and single's growing on it.
I asked my cameraman to pan up to the tops of these repayments,
and I hope what you could see up there was some green blobs and those big spherical green blobs.
Of course, mistletoe and mistletoe is a hemi parasitic plant that plugs into the xylem vessels of
the trees and sucks out some of the water and the mineral ions that they're carrying.
And it does very well in winter because, you know, it's it keeps its leaves all but the truth.
The leaves of the trees,
Gonzo can continue to photosynthesise whenever you get a nice day and the temperature comes up high enough to allow it to do that.
Okay, so these trees have been infested with mistletoe and these are the very same trees just down,
munching away on their roots right now are the caterpillars of the whole at moths.
So just goes to, say, trees, that really might seem like they've got everything going for them,
but there's plenty of things out there that want to actually feed on them.
But there are other things living on the trees that are doing no harm to the trees whatsoever. And that's one of things.
One to look at now on the bottom of the trees, it's really green just on the base.
It's just completely green if we look at that closely for a moment. And that is green algae.
So it's green unicellular algae and it can form a thick coating on the bottoms of trees.
And they're just little individual cells photosynthesising away. Hence their nice green colour,
which I only really see proper algae right on the bottom of trees or in other little corners
where it's been bit shady and a bit damper because algae are very prone to being desiccated.
So they can't just grow on the side of the tree unless they've done what these algae does.
So if you look closely at the book trade at higher up,
you can see lots of bright orange yellow things and some grey green things, all sort of crusty looking.
And these are lichens. And a lichen is a really strange thing.
It's a symbiosis between a fungus and an algae.
So within those lichens, there are little green algal cells trapped inside, photosynthesising away.
But they are being protected by the fungus.
And it's the fungus that can produce some of those other pigments, the bright orange colours, and those are protected.
So you can find out. You can find lichen, sorry, growing on bare rock right at the top of mountains.
Very high levels of ultraviolet radiation still functioning because the fungus can protect the algae.
There's got to be something in it for the fungus and it's going to take some of the carbon that the algae are fixing for itself.
So it's stealing sugars, if you like, from the algae, but it's providing thinks the algae as well as well as protection.
It's really good at extracting mineral ions from the bar or from the rock or wherever it's growing.
So it's a great example of symbiosis. This is the best time of year to see them. They're really popping out from the trunks of trees.
So how many different kinds you can find?
A case was stopped by a line of trees here that have been grow as an ornamental line of trees scream for houses off from the park.
And what's interesting, when you see a line of trees like this one outside of a woodland is that they've got to try.
Always trees are trying to capture as much light as they possibly can in a woodland.
That means growing up, getting a height or growing as tall as you can as quickly as you can and getting your leaves up to that canopy.
If you're out in the open, you're not surrounded by other trees, then the best strategy is to try to grab sideways as much as you can.
That's you can capture light all around you. And no tree does that better than this.
This is Hornby. And look at the incredible shape that it creates.
So it has a really large number of sideways branches going off, and it can almost be wider than it is tall.
So that's home. It's related speech in Oxford. Anyway, there's quite a few places where you can see beautiful lines of home.
So in the past, we have quite a lot of horse chestnut trees. There's very characteristic buds on the horse chestnut.
So they have what are called sticky buds, same big fat buds covered in a sticky substance that's important to the tree.
It wants to protect the buds inside there. And is the new leaf. It's already made and it's getting ready to be pumped up when the weather allows.
So it wants to protect it from any herbivores or insects that might want to come and land on it.
And that's a swell gets stickier and stickier. So I more and more difficult for any insects to come and land on them and stop feeding.
I stopped by. This tree in particular has got an interesting feature. If we have a look here, you can see a branch has ripped off here.
Now, that might have been during storm or it could have been damage caused by a vehicle.
Who knows? But you can see it's really ripped down and it's left the tree badly exposed, pulled off this region of bark.
And this is exactly how funky get into trees. So trees are all susceptible to fungal attack.
Fungi can attract living trees, and especially if they can find a way in light that.
We're gonna go find another tree where you can see the branches cut off better.
And how the tree can actually seal off a wound. Very well indeed, if it gets the chance to stop by another horse chestnut.
There's lots of them in this park. But still, a scanner can see where a branch has been cut off tidily by the Parkes team.
And what you can see is the way the tree is closing up around that cut surface.
It doesn't want to leave that fresh cut surface there. That's the entry point for fungi.
And so it can grow and gradually seal that off. And if the cuts bend nicely and cleanly, it can do that relatively quickly.
And if you look closely on trees, you'll see ones that have been completely healed over.
You can almost not see that once there was a branch there that had been cut off.
And if it's pruning time, you know, if you've got trees at home, apple trees, fruit trees.
Now is the time to prune them while they're dormant in the winter. With very few exceptions, most trees.
Much better to bring them in the winter and do it nicely like base. Cut the branch off close to where it joins the trunk.
Don't go absolutely tight. You've got to leave room for that collar to grow around.
But don't leave a little stump sticking off because that will die. And again, it's written for fungi.
So there are lots of conifers in this park and I dunno what they all are because they will be things from all over the world.
But I just stopped by this one. I do not. This one is. And you can see it's a conifer because it's bearing a little cone.
And that's what conifer means. Cone bearing. So these are Jimeno Sperm's rather than angiosperms of SCD plants.
But they're not flowering plants. They're more ancient than angiosperms. Most the plants we see around us are angiosperms.
These are more ancient than we would have had forests of chimneys, sperms all over the planet in the past.
But the angiosperms took over some time and the dinosaurs were around and basically pushed most of the Jim Sperm's out.
But they didn't manage to push them out completely. So why is it sometimes better to produce needles?
And if you are going to produce needles, should you be evergreen or should you be deciduous?
Because this, you can see doesn't have any needles on it. Right.
This tree is bare in the winter, but it's definitely got cones and it is large and large is a deciduous conifer.
And you might wonder why. Well, the idea is that in temperate Europe, most of our forests are broadleaf trees,
trees that make a leaf for the growing season, and then they throw that leaf away in the winter.
And that's because in the winter, that leaf would skip far too much damage. You know, this far too cold, it's windy.
That root leaf would be wrecked. The conifers instead invest in much longer lived needles.
So they invest a lot in them. They pack them with resins to deter herbivores and are going to last several years.
So why is that the broadly for better strategy?
Well, it seems that in many seasonal climates it's better to just make these cheap throwaway leaves, use them for one season.
At the end of the season, the tree will take back all of the nitrogen that it can and just cast off the carbon that it can remake next spring.
And it will store it in the bark and the roots and use that nitrogen again in the spring when it leaks out.
The disadvantage of that strategy is great is not gonna suffer damage to the leaves over the winter, but when the spring comes, the temperatures rise.
You can't get going straight away. You've got to flush out those new leaves and that takes time.
And as they're flushing out, they're also really vulnerable. Vulnerable to frost.
Vulnerable to herbivores who lay in wait for them. So the conifer needles can get started a bit faster.
But it seems that they're not as efficient as later. The little fir needles don't capture light as well as so many parts of the UK in Europe that the.
Broadleaf 23 wins out. He got mountains in Switzerland or further north, then the conifers,
the evergreen conifers like pines can start to have an advantage as the winter gets
colder and the growing season gets Schwartzmann shorter for those broadleaf trees.
But if you go really, really far north, you start to get this large.
And that's because the winters so harsh and so difficult that you can't even make
a needle that's going to survive the winter without getting so much damage.
And so the needle trees are still in charge,
but they actually throw away their needles over the winter and they just make a cheap needle that will only last a single season.
And they're really beautiful when they leaf out in the spring, they have a really beautiful, fresh green colour.
So if you've got a large growing there, you keep an eye on it. A spring arrives. So the last tree for the day,
I'm standing by something that sort of those kind of kids' toys I remember at some of these old troll things were popular.
And there's a kind of stumpy kind of animal with a massive shock of hair. And that's what happens when you Pollaers Tree and willow.
It's very commonly planted like this. It takes to it quite well. So what somebody has done is just chopped the top of it, chopped all the limbs off,
and adults of those upper limbs will sprout long, thin straight's twigs.
And those were actually incredibly useful. No, we said in the white someone that there used to be a system called coppicing.
I was trying to reinstate in some woodlands around Britain, if you want nice, long, thin poles,
because they're very useful for things that you coppice hazel by cutting it right down to the ground and letting it regrow.
The problem with that is that animals then come and eat the regrowth. So you have to fence and keep out deer.
Now, in the past, when there's a lot more common land in Britain and people have access to it, and they wanted two things from it.
They wanted someone to graze their livestock, but they also needed a source of firewood and timber.
And this was a system that was developed called wood pasture.
And you would basically have grassland, but you'd have intermittent trees like this willow that you would Pollard.
And the great advantage of planting is all that new regrowth is out of reach of my grazing animals.
So I didn't need to fence them all. I don't have my cows wandering around and the trees will go on producing useful timber.
I can come and take off some of that timber. My animals can still graze underneath and the willow never gets big enough to really shade the grass out.
So I guess this little corner of the part that want to recreate the feel of wood pasture where several of these planted willows dotted around.
Okay. Well, that's it for this week. I know we're still in the middle of an absolutely terrible situation.
I urge everybody, obviously, to use the utmost caution. We're always coming out very carefully.
Just me and my son is doing Felmingham, staying well away from anybody else.
And we all have to do that until we can get on top of this hideous virus.
So take care and see you next time. I'm back on biology.