1 00:00:00,300 --> 00:00:07,460 Hello, my name's Lindsay Turnbull and I'm an associate professor in the Department of Plant Sciences at the University of Oxford, 2 00:00:07,460 --> 00:00:11,490 and we're right in the middle of this very serious corona virus crisis right now. 3 00:00:11,490 --> 00:00:17,120 And my students are all stuck at home and we want to keep them in touch with biology and keep in touch with us. 4 00:00:17,120 --> 00:00:46,410 And so we're going to make a new series of videos and they're going to be called back garden biology. 5 00:00:46,410 --> 00:00:49,110 Hello, welcome to this episode of Background Biology. 6 00:00:49,110 --> 00:00:56,370 It's a beautiful, sunny day, Sunday in January, but the sun is shining on us, so that's keeping us all going. 7 00:00:56,370 --> 00:01:02,670 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. 8 00:01:02,670 --> 00:01:08,370 I did a first episode bout that went to white and woods and saw lots of trees growing in a woodland setting. 9 00:01:08,370 --> 00:01:13,740 Perhaps he realised in my local part, there are lots of other trees and more things to see and to talk about. 10 00:01:13,740 --> 00:01:16,000 And I really love the trees in winter. 11 00:01:16,000 --> 00:01:21,860 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. 12 00:01:21,860 --> 00:01:30,600 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. 13 00:01:30,600 --> 00:01:37,680 I asked my cameraman to pan up to the tops of these repayments, 14 00:01:37,680 --> 00:01:42,880 and I hope what you could see up there was some green blobs and those big spherical green blobs. 15 00:01:42,880 --> 00:01:49,410 Of course, mistletoe and mistletoe is a hemi parasitic plant that plugs into the xylem vessels of 16 00:01:49,410 --> 00:01:55,020 the trees and sucks out some of the water and the mineral ions that they're carrying. 17 00:01:55,020 --> 00:01:59,850 And it does very well in winter because, you know, it's it keeps its leaves all but the truth. 18 00:01:59,850 --> 00:02:00,660 The leaves of the trees, 19 00:02:00,660 --> 00:02:07,940 Gonzo can continue to photosynthesise whenever you get a nice day and the temperature comes up high enough to allow it to do that. 20 00:02:07,940 --> 00:02:12,060 Okay, so these trees have been infested with mistletoe and these are the very same trees just down, 21 00:02:12,060 --> 00:02:15,870 munching away on their roots right now are the caterpillars of the whole at moths. 22 00:02:15,870 --> 00:02:19,260 So just goes to, say, trees, that really might seem like they've got everything going for them, 23 00:02:19,260 --> 00:02:23,340 but there's plenty of things out there that want to actually feed on them. 24 00:02:23,340 --> 00:02:27,630 But there are other things living on the trees that are doing no harm to the trees whatsoever. And that's one of things. 25 00:02:27,630 --> 00:02:31,740 One to look at now on the bottom of the trees, it's really green just on the base. 26 00:02:31,740 --> 00:02:37,590 It's just completely green if we look at that closely for a moment. And that is green algae. 27 00:02:37,590 --> 00:02:43,120 So it's green unicellular algae and it can form a thick coating on the bottoms of trees. 28 00:02:43,120 --> 00:02:48,090 And they're just little individual cells photosynthesising away. Hence their nice green colour, 29 00:02:48,090 --> 00:02:52,040 which I only really see proper algae right on the bottom of trees or in other little corners 30 00:02:52,040 --> 00:02:56,910 where it's been bit shady and a bit damper because algae are very prone to being desiccated. 31 00:02:56,910 --> 00:03:02,010 So they can't just grow on the side of the tree unless they've done what these algae does. 32 00:03:02,010 --> 00:03:04,680 So if you look closely at the book trade at higher up, 33 00:03:04,680 --> 00:03:11,610 you can see lots of bright orange yellow things and some grey green things, all sort of crusty looking. 34 00:03:11,610 --> 00:03:15,720 And these are lichens. And a lichen is a really strange thing. 35 00:03:15,720 --> 00:03:19,800 It's a symbiosis between a fungus and an algae. 36 00:03:19,800 --> 00:03:27,790 So within those lichens, there are little green algal cells trapped inside, photosynthesising away. 37 00:03:27,790 --> 00:03:31,170 But they are being protected by the fungus. 38 00:03:31,170 --> 00:03:36,330 And it's the fungus that can produce some of those other pigments, the bright orange colours, and those are protected. 39 00:03:36,330 --> 00:03:41,130 So you can find out. You can find lichen, sorry, growing on bare rock right at the top of mountains. 40 00:03:41,130 --> 00:03:48,000 Very high levels of ultraviolet radiation still functioning because the fungus can protect the algae. 41 00:03:48,000 --> 00:03:54,150 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. 42 00:03:54,150 --> 00:03:59,490 So it's stealing sugars, if you like, from the algae, but it's providing thinks the algae as well as well as protection. 43 00:03:59,490 --> 00:04:06,300 It's really good at extracting mineral ions from the bar or from the rock or wherever it's growing. 44 00:04:06,300 --> 00:04:12,000 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. 45 00:04:12,000 --> 00:04:14,250 So how many different kinds you can find? 46 00:04:14,250 --> 00:04:22,950 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. 47 00:04:22,950 --> 00:04:28,800 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. 48 00:04:28,800 --> 00:04:32,790 Always trees are trying to capture as much light as they possibly can in a woodland. 49 00:04:32,790 --> 00:04:39,010 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. 50 00:04:39,010 --> 00:04:45,970 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. 51 00:04:45,970 --> 00:04:50,550 That's you can capture light all around you. And no tree does that better than this. 52 00:04:50,550 --> 00:04:59,160 This is Hornby. And look at the incredible shape that it creates. 53 00:04:59,160 --> 00:05:06,430 So it has a really large number of sideways branches going off, and it can almost be wider than it is tall. 54 00:05:06,430 --> 00:05:13,730 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. 55 00:05:13,730 --> 00:05:19,780 So in the past, we have quite a lot of horse chestnut trees. There's very characteristic buds on the horse chestnut. 56 00:05:19,780 --> 00:05:28,180 So they have what are called sticky buds, same big fat buds covered in a sticky substance that's important to the tree. 57 00:05:28,180 --> 00:05:36,570 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. 58 00:05:36,570 --> 00:05:40,680 So it wants to protect it from any herbivores or insects that might want to come and land on it. 59 00:05:40,680 --> 00:05:47,440 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. 60 00:05:47,440 --> 00:05:54,370 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. 61 00:05:54,370 --> 00:05:59,230 Now, that might have been during storm or it could have been damage caused by a vehicle. 62 00:05:59,230 --> 00:06:07,060 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. 63 00:06:07,060 --> 00:06:13,270 And this is exactly how funky get into trees. So trees are all susceptible to fungal attack. 64 00:06:13,270 --> 00:06:17,980 Fungi can attract living trees, and especially if they can find a way in light that. 65 00:06:17,980 --> 00:06:21,700 We're gonna go find another tree where you can see the branches cut off better. 66 00:06:21,700 --> 00:06:29,020 And how the tree can actually seal off a wound. Very well indeed, if it gets the chance to stop by another horse chestnut. 67 00:06:29,020 --> 00:06:36,070 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. 68 00:06:36,070 --> 00:06:41,350 And what you can see is the way the tree is closing up around that cut surface. 69 00:06:41,350 --> 00:06:46,030 It doesn't want to leave that fresh cut surface there. That's the entry point for fungi. 70 00:06:46,030 --> 00:06:53,050 And so it can grow and gradually seal that off. And if the cuts bend nicely and cleanly, it can do that relatively quickly. 71 00:06:53,050 --> 00:06:57,010 And if you look closely on trees, you'll see ones that have been completely healed over. 72 00:06:57,010 --> 00:07:01,160 You can almost not see that once there was a branch there that had been cut off. 73 00:07:01,160 --> 00:07:05,890 And if it's pruning time, you know, if you've got trees at home, apple trees, fruit trees. 74 00:07:05,890 --> 00:07:10,990 Now is the time to prune them while they're dormant in the winter. With very few exceptions, most trees. 75 00:07:10,990 --> 00:07:19,210 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. 76 00:07:19,210 --> 00:07:24,100 Don't go absolutely tight. You've got to leave room for that collar to grow around. 77 00:07:24,100 --> 00:07:29,440 But don't leave a little stump sticking off because that will die. And again, it's written for fungi. 78 00:07:29,440 --> 00:07:34,720 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. 79 00:07:34,720 --> 00:07:40,440 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. 80 00:07:40,440 --> 00:07:47,800 And that's what conifer means. Cone bearing. So these are Jimeno Sperm's rather than angiosperms of SCD plants. 81 00:07:47,800 --> 00:07:53,890 But they're not flowering plants. They're more ancient than angiosperms. Most the plants we see around us are angiosperms. 82 00:07:53,890 --> 00:07:58,660 These are more ancient than we would have had forests of chimneys, sperms all over the planet in the past. 83 00:07:58,660 --> 00:08:04,610 But the angiosperms took over some time and the dinosaurs were around and basically pushed most of the Jim Sperm's out. 84 00:08:04,610 --> 00:08:11,230 But they didn't manage to push them out completely. So why is it sometimes better to produce needles? 85 00:08:11,230 --> 00:08:16,390 And if you are going to produce needles, should you be evergreen or should you be deciduous? 86 00:08:16,390 --> 00:08:20,230 Because this, you can see doesn't have any needles on it. Right. 87 00:08:20,230 --> 00:08:27,870 This tree is bare in the winter, but it's definitely got cones and it is large and large is a deciduous conifer. 88 00:08:27,870 --> 00:08:35,530 And you might wonder why. Well, the idea is that in temperate Europe, most of our forests are broadleaf trees, 89 00:08:35,530 --> 00:08:41,350 trees that make a leaf for the growing season, and then they throw that leaf away in the winter. 90 00:08:41,350 --> 00:08:47,050 And that's because in the winter, that leaf would skip far too much damage. You know, this far too cold, it's windy. 91 00:08:47,050 --> 00:08:53,710 That root leaf would be wrecked. The conifers instead invest in much longer lived needles. 92 00:08:53,710 --> 00:09:00,280 So they invest a lot in them. They pack them with resins to deter herbivores and are going to last several years. 93 00:09:00,280 --> 00:09:03,610 So why is that the broadly for better strategy? 94 00:09:03,610 --> 00:09:10,450 Well, it seems that in many seasonal climates it's better to just make these cheap throwaway leaves, use them for one season. 95 00:09:10,450 --> 00:09:18,570 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. 96 00:09:18,570 --> 00:09:24,550 And it will store it in the bark and the roots and use that nitrogen again in the spring when it leaks out. 97 00:09:24,550 --> 00:09:32,110 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. 98 00:09:32,110 --> 00:09:37,780 You can't get going straight away. You've got to flush out those new leaves and that takes time. 99 00:09:37,780 --> 00:09:42,400 And as they're flushing out, they're also really vulnerable. Vulnerable to frost. 100 00:09:42,400 --> 00:09:49,030 Vulnerable to herbivores who lay in wait for them. So the conifer needles can get started a bit faster. 101 00:09:49,030 --> 00:09:57,140 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. 102 00:09:57,140 --> 00:10:03,230 Broadleaf 23 wins out. He got mountains in Switzerland or further north, then the conifers, 103 00:10:03,230 --> 00:10:07,460 the evergreen conifers like pines can start to have an advantage as the winter gets 104 00:10:07,460 --> 00:10:13,460 colder and the growing season gets Schwartzmann shorter for those broadleaf trees. 105 00:10:13,460 --> 00:10:17,660 But if you go really, really far north, you start to get this large. 106 00:10:17,660 --> 00:10:22,610 And that's because the winters so harsh and so difficult that you can't even make 107 00:10:22,610 --> 00:10:27,110 a needle that's going to survive the winter without getting so much damage. 108 00:10:27,110 --> 00:10:29,620 And so the needle trees are still in charge, 109 00:10:29,620 --> 00:10:37,190 but they actually throw away their needles over the winter and they just make a cheap needle that will only last a single season. 110 00:10:37,190 --> 00:10:42,110 And they're really beautiful when they leaf out in the spring, they have a really beautiful, fresh green colour. 111 00:10:42,110 --> 00:10:48,740 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, 112 00:10:48,740 --> 00:10:54,650 I'm standing by something that sort of those kind of kids' toys I remember at some of these old troll things were popular. 113 00:10:54,650 --> 00:11:01,670 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. 114 00:11:01,670 --> 00:11:09,320 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, 115 00:11:09,320 --> 00:11:14,720 and adults of those upper limbs will sprout long, thin straight's twigs. 116 00:11:14,720 --> 00:11:21,020 And those were actually incredibly useful. No, we said in the white someone that there used to be a system called coppicing. 117 00:11:21,020 --> 00:11:24,950 I was trying to reinstate in some woodlands around Britain, if you want nice, long, thin poles, 118 00:11:24,950 --> 00:11:31,160 because they're very useful for things that you coppice hazel by cutting it right down to the ground and letting it regrow. 119 00:11:31,160 --> 00:11:37,550 The problem with that is that animals then come and eat the regrowth. So you have to fence and keep out deer. 120 00:11:37,550 --> 00:11:44,030 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. 121 00:11:44,030 --> 00:11:48,980 They wanted someone to graze their livestock, but they also needed a source of firewood and timber. 122 00:11:48,980 --> 00:11:52,220 And this was a system that was developed called wood pasture. 123 00:11:52,220 --> 00:11:58,040 And you would basically have grassland, but you'd have intermittent trees like this willow that you would Pollard. 124 00:11:58,040 --> 00:12:04,090 And the great advantage of planting is all that new regrowth is out of reach of my grazing animals. 125 00:12:04,090 --> 00:12:10,450 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. 126 00:12:10,450 --> 00:12:17,660 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. 127 00:12:17,660 --> 00:12:26,040 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. 128 00:12:26,040 --> 00:12:32,130 Okay. Well, that's it for this week. I know we're still in the middle of an absolutely terrible situation. 129 00:12:32,130 --> 00:12:38,420 I urge everybody, obviously, to use the utmost caution. We're always coming out very carefully. 130 00:12:38,420 --> 00:12:42,530 Just me and my son is doing Felmingham, staying well away from anybody else. 131 00:12:42,530 --> 00:12:47,090 And we all have to do that until we can get on top of this hideous virus. 132 00:12:47,090 --> 00:13:05,502 So take care and see you next time. I'm back on biology.