Collated information on Ash dieback

I have been asked by a few people what they can do about the Ash dieback problem in the UK, and whilst I said yesterday that there was no official guidance for the general public yet, there are some informative documents prepared by the forestry commission.

Most of these are in the original post I made (HERE), but as they are at the end of a long post, I will put them up on here again, with the new information.

The Forestry Commission has published a visual guide to symptoms: Ash Dieback Disease

The Forestry Commission has also updated its guidance, with information that this is now a quarantine pest, and gives contact details if you think you have come across a site of infection. It also outlines how it is thought that the ancient woodlands have become infected. HERE

I used this Forestry Commission PDF in my original post, it is fairly easy to read and gives an overview: Chalara Fraxinea

The Woodland Trust has updated their guidance since I last read it, with the advice that any suspected infections should be reported at once: HERE

The Government has said that 50,000 trees have already been destroyed: (BBC source HERE)

EDIT for update: There is a website which will be launching Monday at ASHTAG and there will be a smartphone app launching Monday too.  I will post details of that when it arrives.

I mentioned on my fellow blogger Argylesocks post (HERE) that my concern is that with the onset of autumn, we will not know until next year what the extent of the infection is, as the fungus is now in the leaf litter over the winter.

I hope that these are isolated cases in woodlands, but I do not understand why it took from February til late September for this to get attention, or be publicised.

For my non-UK readers, I apologise for the UK-centric posting the last few days.  I am currently writing a post relating to a US issue, so will put that up over the soon.  I will be returning to my evolution based posting next week, but will keep putting up posts of interest to current environmental issues, to go a little more in depth into those.  If you have a story from anywhere relating to environmental or ecological issues which you would like to read a bit more in depth on, you can chuck me an email at squirrellyskeptic at gmail dot com.

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Why mature forests matter..more trouble for the Ash tree.

I wrote a few weeks back about the fungus which is infecting Ash trees in Europe (HERE)

At the time I wrote that  “So far, it seems that the fungus has not managed to infect “wild” trees in the UK, and the government has begun a consultation, which will end on the 26th of October, which could lead to a ban on imports of Ash (and given the severity of the threat, I would hope that a ban is imposed).”

Well, this week it has been announced that the disease has been discovered in  mature forests in the UK, as this Guardian article discusses (HERE).

My last post about this was a bit technical and clunky, so I will try to keep this easier to read.  I want to try to explain as much of the specifics as I can though, because, when I am finding anything out, I like knowing all the details if possible, rather than just understanding the gist of something.

We are going to take a little detour, as I could just tell you that “Mature forests are important” and let you just take that as read, but I would rather run through the reasons behind my claim.

So, firstly, what is a mature forest?

To most of us, a forest is a forest is a forest, but to biologists, and specifically botanists, there is a difference in the type of forest, and it has to do with a term called succession.

Succession can be thought of as the stages of life of an area, whether that is to do with a wetland, a forest, a field etc.

My ecology textbooks define succession as “Replacement of one community by another, often progressing to a stable terminal community called the climax

To illustrate this I will use the example of how a natural forest progresses, as it is one of the simpler ones to picture, but this also applies to planted forests, although the starting point is different there, as we actually initiate tree growth.

Diagram showing forest succession. Image from the encyclopedia of New Zealand

So, we start out with our bare ground on the left of the diagram, which usually consists of some soil, maybe some grass species (those little guys get everywhere).  This bare ground may be the result of a big event like a glacier retreating, or it could be from the drying up of a lake, or the spread of grasses along a sand dune area.  It can also be derelict land which was previously used as an urban area, things are a little more complex in that case, but the basic order still follows.

If we imagine that we have some rocks on the bare ground, and a few tough grasses to start with.  The rocks provide a nice cosy place for some lichen to start living, whilst the grass roots prevent what little soil or sand there is from blowing away.

The lichen cause damage to the rocks, and small particles of rocks fall off and get trapped on the ground by the grasses, and other particles flying around in the wind also become trapped.  As the lichens and grasses die, or get damaged, they fall to the ground, and begin to form a layer.  Eventually, there is enough of this layer (known as humus) to allow mosses to take hold in the area, and as these die off, they too add to the growing layer of dead stuff on the surface, which allows for bacteria to come in and decompose them, adding nutrients to the new soil.

Over time, the nutrients and soil layer builds up, and small, tough plants can begin to grow there.  These are often other grasses, ferns and very small bushes (Box 2 in the diagram). Microbes, insects, worms etc begin to colonize the young soil.

As the soil quality improves (because the plants there die, and are broken down, and nutrients build up in the soil), and the stability of the soil increases due to the growing number of plants, seeds which are blown in the wind, deposited by animals etc begin to be able to grow, and some of these will be from trees.

Initially, only small, hardy trees can grow, but new species come in and as the conditions continue to improve for plants, taller trees begin to take hold.  These do not grow in the earlier stages as tall trees usually require higher levels of nutrients than bushes, or dwarf trees.

Now we have a young forest, and species of animals and birds begin to colonize the area. Trees begin to grow taller, and form a canopy, this leads to a change in the communities of plants which are on the forest floor, and the ones which die off further improve the soil quality.

Finally, we reach the mature forest stage, where the animal and plant communities are stable, and as a tree dies, a sapling takes its place.  In some ecosystems, trees can stay short, like a new tree, for years until a gap opens up in the canopy, then they all race to be the one to take the place in the sun at the top.  Whilst individual trees may change, the overall structure of the forest stays the same at this point, which provides stability for the animal, bird and insect populations, and leads to the forests which we love to walk in.

Whilst the exact age at which a forest is defined as mature varies (depending on the types of trees which are present), a mature forest is several decades old.  If these forests are able to continue developing, they eventually are classified as Ancient Woodlands, which in the UK means forests which have been there for 400 years or so (the current definition of an ancient forest in the UK is forests which have existed since 1600).

EDIT FOR UPDATE: I have found out that one of the woodlands affected is actually an Ancient Woodland, which is believed to have been in place for around 1000 years. Info about Ashwellthorpe HERE

Ok, so now you know why I feel that mature forests are important.  They provide a stable habitat for wildlife and other plants, and due to the length of time which it takes for them to develop, they are not something which is easily replaced.  They also play a role in preventing soil loss from rain or wind erosion.

Now, you are probably wondering why Ash trees are so important, and why the media have been giving this so much attention.

Ash is the fourth commonest tree in the UK, and many forest areas have it as the dominant species. (source: Woodland Trust). Birds such as woodpeckers and owls live in Ash trees, as they are easy for them to hollow out, and they provide food and a habitat for a diverse range of animals, insects, mosses and lichens (For more info, see the Royal Forestry Society link HERE)

Ash woodlands are part of the UK Biodiversity Action Plan, and are listed as a priority habitat in the plan. (See page 60 in this PDF), and they say:

“Mixed ashwoods are amongst the richest habitats forwildlife in the uplands, notable for bright displays of flowers such as bluebell.. primrose..wood cranesbill and wild garlic . Many rare woodland flowers occur mainly in upland ashwoods, such as dark red helleborine.., Jacob’s ladder.., autumn crocus.., and whorled solomon’s seal … Some rare native trees are found in these woods, notably largeleaved lime… and various whitebeams…. Upland mixed ashwoods also harbour arich invertebrate fauna, which may include uncommonor declining species. The dense and varied shrub layer found in many examples can in the southern part of the types range provide suitable habitat conditions fordormice… The alkaline bark of old ash (and elm where it still survives) supports an important lichen flora…. ”  (Latin names have been removed, hence the dots)

Aside from the ecological importance, it has a long history in the UK and Northern Europe, it is suggested as  the “world tree” from Norse Mythology (Yggdrasil) and Ash has been used in the UK since early history, as everything from spears to walking sticks, furniture etc.

So, seeing as these woodlands are on the Priority habitat list, you are probably thinking that the government has taken immediate action on this, and had in fact begun to assess this threat as soon as they heard of it.  Well….not quite.  George Monbiot over at the Guardian has pointed out that the government were made aware of the threat to the Ash tree in the UK some time ago, before the imported infected trees were discovered, and that even importers of Ash trees were recommending that action be taken (link HERE)

So, what is the government in the UK doing?  They have announced that a ban is being implemented starting Monday (link HERE).  Bear in mind this fungus was first found in the UK 8 months ago (February)…. Would it have taken so long for action to be taken if we were talking about infected livestock?

I apologise for the very long post, but I feel it is important that I explain exactly why we need to make sure that we do not lose our Ash trees the way we lost our Elms, and I am very angry at the government response.

Leaves, keys and fungi

So, there was this story yesterday in the Guardian about how ash trees are at risk from a fungus: http://www.guardian.co.uk/environment/2012/oct/04/deadly-fungus-ash-tree-imports?intcmp=122

This topic has been in the media a fair bit lately, but very few of the stories have gone into the mechanisms and details, so I thought I would write briefly about those, as they are fascinating, and can help with understanding the problem better.

Most of the stories in the media have just said that it affects leaves, which is a very vague description.

So, first of all, to make sure we all know the tree we are talking about, this is an Ash tree, otherwise known as Fraxinus excelsior:

Fraxinus excelsior, the common Ash. Image from Wikipedia

And here is it’s close-up (It doesnt get red-eye like I do, and is always photogenic!)

Close up of the leaves and “keys” (fruit) of the common Ash. Image from Wikipedia

So, now we have met the victim, lets meet the perpetrator (Sorry, I am catching up on CSI episodes at the moment, so excuse me if I go a bit Horatio Caine).

This is where it can appear a bit confusing, because this fungus actually has two names:  The one most mentioned in the media is Chalara Fraxinea and it looks like this when it is grown in a lab:

Chalara fraxinea, politely posing in a petri dish. Image from Federal Institute of Technology Zurich

This is the fungus mentioned in the Forestry Commission factsheet about this problem (See further reading for link).

This is what is known as an anamorph, which means it is the asexual reproductive phase of this fungus.

I think the reproduction of plants, fungi and small micro-organisms is really cool, so I am going to explain it a bit here as it can seem a bit confusing (I remember getting tied in knots trying to revise this for functional biology!)

The asexual reproduction of fungi such as this species involves producing spores (from the greek spora, which means seeding, or sowing), which you might know from the puffball mushroom, when you kick it, it gives off a load of dust-like stuff, which is actually the spores for the next generation of the fungus, which looks like this:

Puffball mushroom releasing its spores. Image from wikipedia

Each of those spores is a potential new fungus, provided it lands in a suitable environment for growth.  This method of dispersal is very haphazard, and this is why these organisms produce so many spores.  It is a bit like closing your eyes and throwing a handful of seeds randomly out on a bit of ground and hoping for the best.

They are formed by mitosis, which is also how our cells in our body are replaced and is in itself a really really cool process (especially when you see slides of it), and which I will cover in depth in a later post.

As I mentioned earlier in this post, this fungus has two names, the asexual form C.fraxinea and the sexual form Hymenoscyphus pseudoalbidus. Now, maybe it is just me, but I found it a little confusing initially to understand how one organism can have two names, or even two life cycles when I first started reading about this.

This image shows the life cycle of an Ascomycete, which is the group of fungi which this particular one belongs to.  The asexual cycle is the loop off to the left of the diagram.

General life cycle of an ascomycete. Image from Penn State University

From what I gather from reading several journal articles on this species, it seems that the asexual form is on the leaf litter, and dead wood on the forest floor, and this is not infectious (or pathenogenic to use the sciencey word).

It all goes a bit nasty for our Ash trees when it is in the sexual form, H.pseudoalbidus .  It is called “pseudoalbidus” because there is another species called H.albidus which is not responsible for this problem in Ash trees, but appears physically similar.

This is what the fungus looks like:

H.pseudoalbidus on a branch. Image from Institute of Technology, Zurich

This confusion with two different names for the sexual and asexual form of fungi will be less confusing soon, as in 2013 they are changing the naming structure, so that there is one name for a species of fungi, regardless of which stage of the life cycle it is in.

As you can see from the diagram, the asexual form of the fungus only refers to the spores,  everything else within its lifecycle is classified as H.pseudoalbidus. Calling this C.fraxinea in the media is quite confusing, but understandable, as many journals refer to this fungus as C.fraxinea.

The cycle of infection appears to be, that the spores remain in the litter, or on dead branches over the winter, and then, in the summer, it germinates, and becomes the white mushroom thingies.  These release spores, which are spread by the wind, and some end up on the leaves of Ash trees, and on the branches.  These form structures known as mycelium which are basically a mass of threads, and it is these which are responsible for the damage to leaves and branches, if they get into a gap in the bark, they form lesions like on this branch:

Necrotic lesions on a branch. Image from EPPO (European Plant Protection Organisation)

These are also known as cankers, and result from the death of the tissues.

The fungus also damages the leaves, as shown in this image:

Leaf dieback as a result of fungal infection. Image from EOL

The dead branches and leaves then fall to the floor, and the cycle begins again.

This is a relatively new infection in Ash trees, first being noticed in the mid 1990s.

There are ongoing discussions as to why this has arisen, as this fungus has been known since the late 1800s, but as the non-infectious H.albidus.  There is discussion about whether climatic stress has weakened the trees resistance to infection, or whether the infectious version of this fungus is better suited to the milder climate conditions over recent years, or whether this new infectious form is a mutuation which has arisen recently.

Whatever the cause, the result is devastating. Denmark has lost around 90% of its Ash trees since the infection arrived, and other European nations are reporting large scale losses of Ash trees.  The infection appears to have arrived in the UK (Which is usually protected from these types of infection because of its island status) by importing of young trees which were carrying the fungus.

So far, it seems that the fungus has not managed to infect “wild” trees in the UK, and the government has begun a consultation, which will end on the 26th of October, which could lead to a ban on imports of Ash (and given the severity of the threat, I would hope that a ban is imposed).

Further Reading: (Most are very easy to read, with the exception of the journal article at the end, they are mostly from the Forestry Commission, and similar bodies)

http://www.eppo.int/QUARANTINE/Alert_List/fungi/Chalara_fraxinea.htm

http://www.ethlife.ethz.ch/archive_articles/100408_eschenpilz_per/index_EN

http://www.fera.defra.gov.uk/plants/plantHealth/pestsDiseases/documents/chalaraFraxinea.pdf (Rapid Risk Assessment)

http://www.forestpathology.ethz.ch/research/Chalara_fraxinea/index_EN

http://www.forestry.gov.uk/pdf/pest-alert-ash-dieback-2012.pdf/$FILE/pest-alert-ash-dieback-2012.pdf

http://www.forestry.gov.uk/chalara

http://www.guardian.co.uk/world/2012/oct/07/disease-killing-denmarks-ash-trees

Krautler & Kirisits: The ash dieback pathogen Hymenoscyphus pseudoalbidus is associated with leaf symptoms on Ash species (2012) http://www.academicjournals.org/jaerd/PDF/Pdf%202012/14MayConf/Kraeutler%20and%20Kirisits.pdf