My name is Anne Edwards and I'm a plant biologist and microbiologist
at the John Innes Centre in Norwich.
We're standing in Ashwellthorpe Lower Wood, an ancient woodland in Norfolk.
It is about 100 acres in size, and about 40-50% of the trees in the wood are ash trees.
So behind me there's a very large ash tree, it's a female,
you can see the seeds hanging from its branches,
and Ashwellthorpe actually got its name from the Vikings,
for whom the ash tree was a sacred tree,
it was very important part of Norse mythology.
We know that ash dieback is caused by a fungus, and it's spread by spores
that land on the leaves in the summer.
It kills the leaves very rapidly and they fall on the ground,
and the fungus continues its growth through the branches,
growing throughout all the vascular tissue, strangling the tree.
And the fungus also carries on living on the fallen leaves,
and produces tiny mushrooms that are ready the following summer
and these release millions of spores to infect other ash trees.
This is a healthy ash branch, you can see the smooth grey bark.
In this instance the fungus has killed all this wood here
and this is the leading edge of the fungus just here, which is going black.
The fungus pathogen is called Hymenoscyphus fraxineus,
and it's come from Asia where it lives quite harmlessly on the Asian ash tree.
When it was brought to Europe it couldn't find its normal host,
so it it colonised the closest thing which was the European ash,
and for some reason it has had this devastating effect,
it's far too invasive for our European ash.
This is a coppiced ash, and although the limbs are probably about twelve years old,
the base, what we call the stool, is well over a hundred years old.
And this tree is completely dead, it died very very quickly,
it got infected in 2012, three years later it was completely dead.
The fungus has ripped through all these trunks very very quickly.
But other trees in the wood haven't reacted like this.
Some are clearly infected, but they haven't died.
And there seems to be a whole spectrum of tolerance to the fungus
in the trees in this wood.
This tree here, the limbs are the same age as the one we've just seen,
but it's much more healthy.
It's very close to the one that has died,
so it's very likely that it's seen the fungus and been challenged by the fungus,
but it hasn't reacted in the same way.
Its trunks are very healthy, apart from a few deer nibblings here.
And we're very interested to find out why that should be so.
So when we knew there was a problem here in the wood in 2012,
I took a small sample of infected wood back to the laboratory at John Innes
and confirmed that we had this ash dieback outbreak.
At which point I asked for help from my colleagues at John Innes,
but also in the Sainsbury Lab and the Genome Analysis Centre.
We realized that we were at the center of an epidemic
that was going to sweep across the UK, and that we had to do something.
It's been estimated that the UK has 80 million ash trees, maybe 80% will die.
This disease came in 2012, just three years ago, and since it arrived
we've learned quite a lot more about the fungus, how it lives its life,
why it has such a devastating effect on the ash trees.
We have to accept there are going to be changes to our landscape in the next ten years,
we hope that we can rebuild the population of ash
with a tolerant set of trees that still show genetic diversity.
So they can withstand climate change
and anything else that comes to challenge them.