Ash Dieback Special - Ecology and Hope with Dr Cecilia Dahlsjo and Dr Jo Clark

The ash tree plays a huge role in Europe's culture and ecology. From Yggdrasill, the giant ash world tree of Norse Mythology to the Guardian trees of Ireland; the ash tree has been a central part of European folklore and mythology. It can be a prolific natural regenerator making it an excellent species for timber and its flexible, white wood is still in high demand today and is used in the manufacture of Morgan cars, Irish hurling sticks and numerous items of furniture and carpentry.

However, the European ash tree is now facing the most significant modern threat to its survival. Ash Dieback (Hymenoscyphus fraxineus) was common in China and Asia (where native ash species have obtained tolerance over time). In a globalised world, where timber and plant material are constantly being transported; this has sped up the spread of infectious tree diseases and pests. Ash dieback has ripped through Europe and was identified in the UK in 2012. Many UK  ash woodlands have since been decimated by this disease which resulted in some very gloomy headlines:

https://news.exeter.gov.uk/diseased-trees-to-come-down-amid-safety-concerns/

https://www.theguardian.com/environment/2022/oct/16/ash-tree-dieback-uk-woodlands

It is unequivocally a monumental threat to our woodlands and will have major impacts for our ash trees and the species that associate with them.

In this podcast, we take a closer look at ash and the effects of Hymenoscyphus fraxineus. We discuss the threat without hyperbole of some headlines and look at the ecology of ash and what will happen to our woodlands as we lose large numbers of these trees to disease. We also offer signs of hope, the living ash project from the Future Trees trust is working with nature to speed up the ash trees ability to fight back. While there's no doubt that ash dieback is a major economic and ecological threat and will dramatically change the nature of our woodlands; we try to take the longer view and understand the likelihood of the ash species to become tolerant over time and take a more nuanced look at the ecology. There is no 'good' or 'bad' only change. The more we can understand the science and the effects of tree diseases, the better placed we will be to manage the threats and identify strategies to resist threats or adapt our ecosystems to a rapidly changing future.

This podcast was co-hosted by Dr Cecilia Dahlsjo who is studying the effects of ash dieback through her work at Oxford University and Dr. Jo Clark who is the head of research for the Future Trees Trust. They run the Living Ash Project which is leading the way in the UK in developing ash dieback tolerant species to help nature rebound from this new threat.

The Leverhulme Centre for Nature Recovery is interested in promoting a wide variety of views and opinions on nature recovery from researchers and practitioners.

The views, opinions and positions expressed within this podcast are those of the speakers alone, they do not purport to reflect the opinions or views of the Leverhulme Centre for Nature Recovery, or its researchers.

The work of the Leverhulme Centre for Nature Recovery is made possible thanks to the support of the Leverhulme Trust.

Transcript

stephen thomas: 0:06

Welcome to the nature recovery podcast. We're going to take a closer look at some of the solutions to counter biodiversity decline. And we'll find out more about the people behind these ideas. Hi, there, my name is Steven Thomas, and welcome to the nature recovery Podcast. I'm really glad today that my guest host is Cecilia. And we're

Dr Cecilia Dahlsjo: 0:43

Thank you so much for having me. I run a project in Whytham Woods. And if people don't know why Whytham Woods, it's one of the most studied ecosystems in the world. So since 2017, we've been working there looking at the impact of Ash Dieback So Ash Dieback was detected in looking at what is the impact of that increasing light penetration on the habitat structure, so what's on the ground vegetation on the ground? And then those things linked to Woodland connectivity. So our third focuses would look on activity of bats, birds and mammals, and how that's affected by

stephen thomas: 1:56

Okay, that's amazing what's happening in Whytham. And I'm guessing that's not your only area of study and research other other ecosystems that you look at you at the moment?

Dr Cecilia Dahlsjo: 2:07

Yes, we're doing a lot of things actually. So being part of the Leverhulme Centre for Nature Recovery, where we're still looking at Woodlands, but we're also starting to explore the farms a bit more around the university. So we've we're in the process of setting up a lot of exploring and looking at in terms of biodiversity, but also in terms of carbon and impacts of tree planting and that kind of thing.

stephen thomas: 3:00

But that's a wealth of different study that you're doing. I know grazing at the moment is a hot topic. But back to the ash tree. Now, I am biassed because the ash tree I think is one of my favourite trees in in a woodland. There's good reason for that. So, you know, oak seem to get these sort of myths wonderful, but we have, you know, our own European myths. And I think so. The fact that the ash tree features and these mysteries that you know, it has been prevalent in human society for such a long time, which makes it almost more heartbreaking that it is facing this rampant you get the strange you know, if you were designing like a fantasy forest with a glade and having some l fish kind of creatures around I think you would have some ash trees there for just aesthetic reasons. And but going back the ecology about that does that, you know, is that quite different to

Dr Cecilia Dahlsjo: 4:53

Yeah, so I think you're absolutely right. If you're looking at a beautiful woodland so different from an ash woodland And I love ash as well. I'm a I'm an ash fan. So yeah, so what we're looking at is actually what you've just described. So the difference ecologically in terms of ash habitats versus different other habitats like oak habitats or beech woodlands, or mixed woodlands in general, in terms of species But where Ash is important, I think, is the ecology. So like you say, Ash Trees have a more sparse canopy. And that's a due to the canopy being a little bit smaller. But it's also because they have compound leaves. And that's when they have sort of fingers, sort of little leaflets. So there's through that, we have data that shows that in a beech woodland, for example, most of that biomass is in the canopy, but in an ash wood, and most of the most of that biomass will be on the ground in terms of understory and that's because of that light coming through.

stephen thomas: 6:28

Okay, so that's interesting as a scientific reason why I like to walk in ash woodlands, because I can see more around whereas in other woodlands that might be more species, but the kind of within the tree trunks or within the canopy or so on,

Dr Cecilia Dahlsjo: 6:40

that's a good explanation. And and there's another reason why Ash is so important. And it's it's very unique, in that the ash leaves, they fall green. So normally, you'd have a discoloration of the leaves and then they fall off the ash, they actually fall green. And they fall well is that the decomposition of ash leaves is much, much higher. So it actually would decompose in about five to six months, while an oak leaf or a beech leaf will decompose in about seven years. So there's a huge difference. And maybe you've noticed as well, that when you're walking around a Sycamore, beech and ash. And what we found is that in an ash woodland, all of those species decompose faster, then in a mixed and woodland, so a beech leaf would decompose faster in an ash woodland than he would in a beech woodland. And that's because in an ash woodland, you have a very high quality

stephen thomas: 8:36

Okay, and I remember reading some I don't know how if this is true or not, but it's leaf litter can affect the soil chemistry and create an environment that promotes the conditions for sort of more successful ash regeneration. Is there any truth to that? Or

Dr Cecilia Dahlsjo: 8:53

yeah, so if you're looking at the topsoil because that's what's going to be affected most, if you have in an ash woodland, for example, we see that the macronutrients are higher than they are in a non ash woodland. So for example, a beech woodland. And that is because the data and all our experiments is that the system as a whole in terms of ecology and nutrient cycling, and those sorts of things. It will slow down. So decomposition in habitat will slow right down as you're losing ash because you're changing from highlight environment, high nutrient high,

stephen thomas: 10:05

Okay, and so that um I guess that brings us on to the actual the the state of ash at the moment and ash die back which is you know unquestionably if you're an ash tree currently not not I know scientists take what sort of human personification but it's not looking good for Ash at

Dr Cecilia Dahlsjo: 10:47

Hymenoscyphus fraxineus

stephen thomas: 10:48

That's the one - it rolls off the tongue really easily. But so there will be affected by it. But that doesn't actually mean that they're going to die. And it can take a long time for mature ash tree to I think, you know, kind of 10 years, you know, for me, I hadn't hadn't seen it seems to be that it is kind of everywhere, but some trees still look really, really healthy. Whereas a neighbouring tree is looking, you know, there's a there's a much smaller canopy on it. So it is affecting everything, I guess at the moment, is it it's all over the UK? Or is it just vastly

Dr Cecilia Dahlsjo: 11:56

Yeah, no. So So I started back was first detected in the UK in 2012. But actually, there's some evidence, I've read some papers that show that you might actually have been here, since around 2004, that might have been a slow increase. And then from 2012, we didn't get it in found at the beginning too. And since having read more about it, there's some really good studies who've done because Astro Beck has been around in the in Europe for a very long time since the early 1990s. So there's now some really good sort of Pan European Studies, looking at the mortality rates there that isn't particularly known yet. But the average tends to be 70%. But like I said, Joe will be able to talk about that a bit more.

stephen thomas: 13:41

Well, that sounds like a perfect point that I was lucky enough to speak to Dr. Jo Clark, where the future is trust and she is responsible for the living ash product. So this is my conversation with her. So my guest today is Dr. Jo Clark. Joe is Head of Research for the future products. So welcome to the podcast. Jerry, thank you for being here.

Unknown: 14:33

Thank you very much for having me, Steven.

stephen thomas: 14:36

So yeah, just to kick off, could you tell us a bit about the feature trees trust, and then maybe more specifically about the living ash project and what you're doing? Yeah,

Dr Jo Clark: 14:46

Future trees just we're a really small charity. We're really interested in forest genetic resources and the material that gets planted in our forests and woodlands. People may not know but all trees planted for forestry purposes are governed by the Forest reproductive material which I think is why we're here today, which we lead. So we use trees trusts were established about 30 years ago. And in fact, Ash was the first species that we worked with. And we've been working with ash for over 30 years. So we've got a very large, very genetically diverse collection of ash, tolerant to the fungal pathogen of ash diabetic. It's funded by Defra within our second five year funding phase. And it's a large collaborative project with many partners. Our primary partner is Forest research, who've been working on Ash BiPAC for a long time. But we're also working with more

stephen thomas: 16:39

That's amazing. I'm a huge fan of ash, woodland and ash, wood and communities. And I was there's some lovely examples within Oxfordshire. And if you go into woodlands, you depending on where you go, you see ash trees in various different stages of sort of facing the threat. what are the things that you're looking for? When you talk about tolerant trees?

Dr Jo Clark: 17:22

Gosh, that's a lot of questions. Well, so Ash is a really important tree species, particularly in England for ecological reasons. So it's before Ash dive so ash died back arrived in 2012. Officially, although we now know it was actually here before that, but while it was still an active are obligate on Ash, this means they don't live on anything else other than ash. And many, many other species are highly associated with ash. So if we lost that Ash, it would be a real problem for those obligate species, they would have nowhere else to live. And those highly associated species will species, I believe, and the living ash project, if we did nothing at all, because of ash is so genetically diverse, I am almost 100% confident that we will still have ash trees in the future. However, the living ash project is trying to shorten natural processes, if you like that natural selection tree didn't get the disease at all, and we know that all trees get it. Thus they exhibit the symptoms in various degrees. And therefore we say I like to say tolerant because they've got the disease but they're actually dealing with it and we can see through Control inoculations, that you if you, if that you know that that big tree has to be hit many, many times with with many infections before it really starts to die back to a significant effect.

stephen thomas: 20:37

But that's interesting to hear and sort of understand the as it as a disease. I mean, we all can get diseases, but some of us don't even notice it when we get it and we all carry on living and growing and for trees. There's there's similarities there. detected a note of cautious there's the potential of things like the emerald ash borer or climate change is a whole other thing and you know, droughts and threats and my understanding isn't it isn't the ash Diabate the nursery kills that tree, it can weaken it, and then other diseases and funguses can can come in and

Dr Jo Clark: 21:51

Yeah, there has been an incredible amount of hype over this. When it first hits, it was quite astonishing the degree of media interest because forestry has typically not really garnered that level of interest. And there does seem to be quite a lot of doom and gloom, but it and it is, in urban settings. So there's an awful lot of ash trees out there. So unfortunately, we we I think we will, we have lost a lot and we will continue to lose a lot. But we are definitely finding trees with which are dealing with the disease much better than others. And this is where I think the living together in a breeding programme, that maybe in 10 years time or so we will have healthy ash trees with which we can, you know, repopulate woodlands, and keep ash a species for ecological purposes, but also for forestry purposes. So although although there is there it is pessimistic, I don't think population. It's a big population, and we can therefore breed our way out of it.

stephen thomas: 24:14

Yeah, and I always find that unusual that we think of things, you know, we think of trees and very human terms. So for my generation, that probably will be a devastating loss of ash in woodlands, and that will have ecological impacts. But I guess if you think of things in tree terms, mentioned there you're kind of bringing together potentially trees that you've identified as tolerance and and trying to read them I don't know how long it takes to kind of get those sort of weather the saplings and stuff to maturity. If you did have driven tolerant ash seed source that was quickly you could produce the source if, if all went to plant?

Dr Jo Clark: 25:37

Yeah, so So again, you pack a lot of questions into your so within the living ash project, we have a number of work streams. So I've been talking about finding that tolerant material. And we've been funded very generously by Defra from 2013 to 2018, to screen that breeding population that I mentioned of those 40,000 trees, and we also at that point, use pressures do the screening for them. So at the end of 2018, between those two projects, we grafted about 1000 individual trees, and we planted them in an archive on the National Forest state in Hampshire. And we continue to monitor that archive and forest research continue to monitor some of them are promising. So we will draft up, we do grafting because it always works. So there's been research on how to bulk up material, how to get it on its own roots, how to get ash into cuttings, and it's actually quite difficult. We forest research did some tissue culture trying to get trees onto the you because we make these selections on what the tree looks like, and because we select them in areas of high infection, we think our selections are good. But there is a very, very, very small chance that that tree has actually not come into contact with a disease yet so so it may be disease escape, we what they want to do how they want to take it forward. But we're looking at potentially grafting up the best tolerant trees to plant out into grafted seed orchards so that our best tolerant trees can interbreed with each other. And then you'll get seed from those grafted seed orchard. And because road. But potentially we could be looking at sort of eight to 10 years.

stephen thomas: 29:39

Wow. I mean, that's just hearing what you've done. The amount of work that's gone into that and the amount of trees and just even managing that as an operation is really really impressive. And it gives me a lot of hope I didn't you know, obviously it's not we're not going to fix significantly. I mean, I think everyone outside of ash, which is probably my favourite, I think lots of people are very fond of oak and oak is, there's some real challenges for Oak and pretty much every Broadley tree out there seems to have some kind of pests or disease. But I still, I guess, we control is increasing threats coming into our woodlands.

Unknown: 31:10

Some days I feel a bit, there's there's so much there are so many novel pests and diseases that we've not had. And the rate of their introduction is really quite, quite scary. And with with climate change, I think a lot of these things that maybe might not have found Britain such a already here, that they're on the horizon. You mentioned the emerald ash borer, which is, which is a worry and xylella on oak and the, you know, on the olive trees in the Mediterranean regions, that's a worry. I mean, I can give your another specific example is we also work on sweet chestnuts, orchard, it's really problem if if your fruit is not touring, and it's really difficult to get people you know, we're so under pressure, you said, is science keeping up? And in a way, I'd have to say no, because there are quite a lot of these things out there. And it's hard to get people interested although you asked about industry, and I'd like to think that most professional foresters are pretty good in the Forestry Commission, promote there, keep it clean, campaign, you know, wash your boots, wash your kits, your harvesting kit, when you go from site to site. But a lot of these woodlands, woods. So I think we do have a large education issue that we're probably not dealing with to the best, what to the level that it needs to be dealt with. I

stephen thomas: 34:20

think just understanding more in the consciousness that really our woodlands are under threat. Climate change can speed things up. And yeah, you mentioned Sitka spruce. I mean, from an economic point of view, we rely pretty much on this one tree certainly Scotland does. And you know, imbedded carbon, if we want to have less cement, you know, timber is really important, and we're still importing lots of timber. So, you know, a really good thriving woodland. forestry industry is really important for so many measures. But to have that you need healthy trees. It's it's

Dr Jo Clark: 35:31

No, but I agree with everything you say there. And I think it's really important that I think we're seeing a shift in the last 10 years and public education is really important. And I think we need to understand that actually, it's a good thing to cut down trees. And I can almost hear people go, shock horror, but actually timber and wood products is one of our biggest imports. With And if you bought improve material from like improve Sitka spruce or the improved material from future trees, trust breeding programmes, you can actually get a really good crop that you can make some money out of heaven forbid that dirty word

stephen thomas: 36:41

I'm about to ask you about. I've seen some stuff, some papers about, you know, bacterial associations with trees turning to rash and I think some people were talking about, you know, are there any other things that you're looking at? You know, additives inoculations, that you've seen Ash dieback, which I'm not sure are practical, from a from a sort of a forestry intervention? Because I think there would be too expensive if, if you had to apply them to every tree?

Dr Jo Clark: 37:23

I think I think there are there, there's ash dieback isn't just one thing. It's not just one fungus coming onto a tree and killing it. There's a lot of interactions going on soil interactions, microbe interactions, there's a lot to do with the silviculture, where the tree is growing research on all these other aspects but we're really interested in finding trees that are already displaying tolerance that we can breed from. Okay.

stephen thomas: 38:16

We were talking a bit about you know, woodlands, visiting woodlands and seeing felling and I think currently if you go to any woodland certain in the south, there is a lot of ash tree felling, I think most of the felling you would see would be ash for mostly for safety reasons. You dangerous of infected trees, that sort of things can snap in strange ways. In other cases I've done and Warburg which I think is the I think it's the Woodland Trust, or it might be Bebout. They have a reserve there and they've done the safety felling but they can't afford to federal the ash trees, or the other way. But I'm just interested from your perspective, given what you know, and giving you a slightly optimistic outlook if you if you had the luxury of owning your own ash dominated forest and you saw the signs of infection, what would kind of be your reaction and the approach that you

Dr Jo Clark: 39:51

I think there are two different issues here. One is commercial forestry. So a lot of landowners who manage their woodlands in a you know, a managed way too. For a timber resource, and then you mentioned Walberg reserve. So that's like a nature reserve where you have a lot of people legal duty of care, and it would be irresponsible not to. On a private estate, again, that's that's slightly different matter. And you're you have the luxury of doing what you may want to do. So you may want to sell your ash quite quickly before the fungus gets into the mainstem. Because Ash is a really diseased trees, and they've removed them, leaving the healthy ones. And that might mean that they have to go back and do more, more felling in five years time trees die, but but they're also leaving the very best a for biodiversity. And that's a niche environment. And be that maybe, you know, die back, as long as it's safe to do so. Because as you mentioned, that's good Deadwood, habitat. And also, they may just be leaving that that one or two trees there that could be tolerant that could really help keep ash as a species for the future. So I think you've got to look at who visits and

stephen thomas: 42:27

no, definitely I agree with all of that. And just, uh, you know, if you fell on our street, it's got a sort of a 0% chance of showing tolerance. But then again, you know, not everyone has that kind of luxury of having time. And for you all, for us. And all standards can be very, very nature and with with natural processes to speed up the recovery of a native species that creates, you know, these beautiful woodland areas, and, and is a very important economic crop for our timber industry. But for you, if I said the phrase, you know, nature recovery, which is quite a loaded

Dr Jo Clark: 43:24

Gosh, well, I suppose in its literal sense, I would think it's trying to restore eroded habitats, so that species that live in that habitat can thrive. And it could also mean, like connecting, like corridors to connect woodlands together, helps nature to recover, if you allow recovery. And that comes down to people education, and like some pellets are no longer, you know, acceptable. So that means I hedgehogs don't get poisoned, which is a good thing. Maybe I suppose from a forestry perspective, I would say that nature recovery means education by telling people it's

stephen thomas: 44:48

Yeah, I love it. And I love the fact that we've asked this to every guest and no one has given us a deal. Something completely different. Everything about and I asked people in the street and sometimes they do See, I don't know what it means. So it's it's a very interesting, it's quite a new phrase. But I think I think it's ambiguity has its power, it can actually be a phrase that can bring people education is so key to that. So last question, I'm so grateful for your time, it's been really interesting to talk to you. So finally, if I could give you a week spend, there's no judgement here. If you if you choose, if you choose the Seychelles on a tourist, that's fine. But you've got to choose an

Dr Jo Clark: 45:58

Well, of course, being in forestry, I would love to go anywhere with with with, with big trees. And in fact, I've been to quite a lot of places with big trees and like the California and redwoods is is blows your mind away. But if I could go anywhere, I would like to go to Patagonia,

stephen thomas: 46:32

This is a shout out to any researchers and funders, if you need an experience, forestry, genetic resources, and head of research to come and look at trees in Patagonia. Jo is your person that has been amazing, I've learned so much. And I'm so glad that you and your team are working hard. I love lush woodland, I'm gonna be watching it, it will decline I know. But I feel really happy that my children and

Dr Jo Clark: 47:08

That's great. Thank you so much for having me on to talk about the project.

stephen thomas: 47:13

So that was a fascinating chat with Joe. I hope you enjoyed that. And it left me you know, while unquestionably it's not a great situation, and we are seeing vast declines and ash trees, and that's going to have huge effects. It's really heartening to know that in terms of generations. But in the meantime, you know, I guess what's going to happen with our woodlands is going to change. And I suppose with all these ash trees losing their leaves or dying, you're going to end up with a lot more light coming through, and I guess a lot more standing dead wood. And that's

Dr Cecilia Dahlsjo: 48:26

Yes, I think it's it's more nuanced than that. In ecology, as everything is it's change. And change is good for some people in the good for some and bad for others. And so there's both winners and losers on both sides. I think it also depends on the timeframe that you're looking beginning, I would say that the winners there would be small mammals and small birds, because they are much more. So small mammals or small birds would be able to hide a lot better in that high understory, which means that they can spend a lot more time feeding them thinking about their leaflets on the ground as you get other species like beech and oak coming in, and that's going to have, it's not a negative effect, it's just a different effect. So you'll have that a less nutrient rich soil, for example. So it's just a change and, and with that change will also be changed in

stephen thomas: 50:20

Okay, so I can see go to take my children to woodlands, and we'll be able to pick more berries off of Bramble and stuff,

Dr Cecilia Dahlsjo: 50:28

there's also differences in microclimate. So for example, in a Nash region where you've got a lot, a lot of light and less protection from that canopy, you will have a higher variability in microclimate. So it will be a lot hotter, and during the night, it will be a lot some there was a PhD student a few years ago, now that they're looking at ash died back in white, and this was before Ash died back had even was even detected in the woodland. And she was remarking a few trees to see if the decline of them would have an effect. And that was in a mixed stand. And so

stephen thomas: 51:50

I guess I'm also interested as well with you know, when trees do die, I know because from a forestry point of view, there's a lot of pre emptive felling. And so there's a lot of safety funding that has to be done because ash trees are dropping their branches. And I think the wood is what doesn't increase of standing that would seem to do to a, to a forest. Yeah, no, I

Dr Cecilia Dahlsjo: 52:37

think it's amazing, actually, it's, I love dead wood. And I think it's really important to keep the tree standing if if you can, if it's not a health and safety hazard. So dead standing wood is very good, at in particular is quite softwood. So when that dies, and becomes a bit ground, they will then start decomposing and there'll be earthworms that go into it and start living in it and hollowing it out and more beetles and different species that can make it its home. So I think it's a good thing to keep it there.

stephen thomas: 53:41

Yeah, I mean that well, this is why I love talking to ecologists and ecology experts like yourself, because, you know, from the very you kind of zone in you look at a media report, and it's like yeah, ash trees are dying. This is a terrible thing. This is a bad thing. There's a lot not just death is change, right? And with every with every dying tree that gives more habitat to beetles to fungus and just sort of seeing the whole cycle of things. And like a tree falling in the forest always think of it as like a like a whale fall in the ocean. It's like this huge source of And, and our world is in rapid change. And some of these changes, the more we learn about them, the more we can understand that there are there are some benefits that change and working with that we can promote the benefits. And also the more we can learn about what you know, what are the harms,

Dr Cecilia Dahlsjo: 55:26

I think that's excellent. I'll just maybe finish on saying that I always think about ecosystems as change, as you say, and I think that's a really good way of looking at it. And I think the more chaos you have in a habitat and an ecosystem, the healthier it is, because it

stephen thomas: 55:44

Well, that is a wonderful note to tell on and on. And I will tell my wife that we need more chaos in our in our domestic ecosystem, because we have plenty of it. But Cecilia, thank you so much for your time today. And thank you for joining me on the nature recovery podcast. Thank about the activities of the libre Hume Centre for nature recovery. You can find us on Twitter at nature recovery, or you can visit our website for more information. That's www but nature recovery that ox.ac.uk Thanks so much for listening