“Yggdrasil, the World Tree, grew on an island surrounded by the ocean, in the depths of which the World Serpent lay. This ash tree’s trunk reached up to the heavens, and its boughs spread out over all the countries of the Earth. Its roots reached down into the Underworld. A squirrel ran up and down the tree carrying messages from the serpent gnawing at the roots to the eagle in the canopy, and back. A deer fed on the ash leaves and from its antlers flowed the great rivers of the world. A magical goat grazed by the tree, and its udders dispensed not milk but mead for the warriors in Odin’s Great Hall. The gods held their councils under the canopy of their guardian tree.” Trees for Life.org

In my role as Countryside Ranger Apprentice (what's this?) I am following arborist Graham Joyce up a rocky path up the Bovey Valley Woods, looking down on the River Bovey as its slow summer waters tumble over the mossy granite boulders. He stops along the way to look searchingly into up into the canopy and every now and then clambers into the undergrowth to examine the base of trees. Some trees will have their trunks tapped with a hammer, listening out for the dull sound rotten wood makes, others will have an identification number tagged onto them, others will be marked with an orange spot, marking them for felling.

He is carrying out an annual tree safety inspection, assessing the risk posed to the public of the trees in the East Dartmoor Woods and Heaths National Nature Reserves. He takes into account the amount of public use of the path or ride adjacent to the tree in addition to the health of the tree itself when deciding on what action is required if any. The risk of a moderately small limb falling into a road is given far greater weight than the risk of an entire tree coming down far from any paths in an unvisited part of the woods. If a tree is likely to fall but is so far from any path that the risk to the public is so minute than no action will be required and the tree will be left to decay naturally.

The trees that receive by far the greatest attention and make up the majority of the felling and de-limbing work specified are the Common or European Ash (Fraxinus excelsior, of the olive family Oleaceae). This is due to the spectre of Ash Dieback caused by the fungus Hymenoscyphus fraxineus. Tree safety assessments taking place in the summer months are able to use the foliage to spot early signs of Ash Dieback as blackening and wilting of leaves and shoots is one of the first symptoms a tree may be infected. If the infection spreads into the twigs, limbs and even the trunk it will cause the formation of dark lesions or cankers with a characteristic elongated-diamond shape. If these wrap around the entire limb or trunk the flow of nutrients and fluids from the roots can be cut off entirely leading to dead and ‘embrittled’ limbs being held up in the canopy that can fall and cause injury.

Arborists dismantling the crown of a die back afflicted Common Ash

Ash Dieback caused by H. fraxineus is widespread in continental Europe and Ireland and is present in most parts of the United Kingdom, its effects being most visible in those areas where it has been present longest and where the conditions are most favourable to the fungus. It is estimated that we will lose 80% of our ash trees and the loss of tens of thousands of these trees will cost an estimated 315 billion in practical felling and clearing, and in the loss of ecological services that the trees fulfil.

Dieback could have a devastating effect on woodland and hedgerow biodiversity, with ash trees’ airy canopy and late-opening leaf letting plenty of sunlight through to flowers of the woodland floor like wild garlic (Allium ursinum) and dog violet (Viola riviniana) that are vital for insects such as frittilary butterflies. The drooping, winged keys that are seeds of the ash tree are food for bullfinches; and nuthatches, owls and woodpeckers make their home in the ash. Their smooth, grey bark is alkaline and with the right conditions will be covered mosses and lichens, which are features of . Many different moth caterpillars use the leaves as food.

Mosses adorn a heavily pruned Ash

The timber from the ash tree has many uses both traditional and contemporary. Its strong, flexible timber has traditionally been used for carts, chariots, wagons and carriages and these strong but flexible properties are why it was commonly used for oars, spears and arrows, and the construction of agricultural technology, and is still favoured for the handles of axes, hammers and garden tools. It coppices well, providing bean poles, and when older, the long ‘hop poles’ traditionally used to support the wire hop vines were grown on for the brewing industry, and the ten-foot high stilts the workers walked about on to install them.

The World Tree of Norse Mythology, Yggdrasil, was an Ash tree, with its roots in the underworld, its branches in the heavens, and mead-producing goats grazing its leaves. A spoonful of ash sap was given to babies on leaving their mother’s bed for the first time, and sickly children were passed through a cleft ash to heal them. Were a cleft was made in a tree for the purpose, the cleft would be bound back together, to heal along with the afflicted person, thereby linking the fate of tree and person.

Monolith Ash

So, what future for the Tree of Life? Well, in the short term, you will see a lot of ash trees being heavily cut back and felled. It takes about 3 years from a mature tree first showing signs of Dieback to a loss of canopy so severe the tree won’t recover. A tree which has lost half its canopy will have much dead wood in the canopy making it dangerous to work under and the fibres of the trunk will have become embrittled and this makes felling unpredictable and more dangerous. This means that many landowners and managers will prefer to fell ash trees at the first sign of dieback before they become dangerous and require more expensive felling, often including machinery. In woodlands managed for timber production this may mean clear felling stands of ash so that new trees can be planted and the land be brought back into productive use. In the Bovey Valley the woods in the NNRs are managed for nature conservation and so the great benefit to biodiversity from standing deadwood means trees with dieback that don’t pose a threat to the public will be left standing and will transition into a great habitat for birds and invertebrates. Trees that are within falling range of footpaths and roads that do pose a threat to the public may be de-limbed until only a standing ‘monolith’ remains, providing habitat whilst minimising the risk from falling branches. Through a tendency to ‘tidy’ our woodlands and extract timber for lumber, our woods nationally tend to be lacking in deadwood, which provides nesting sites for birds, habitat, food source and ‘refugia’ for invertebrates, and eventually will be broken down to provide nutrients for growing trees. Ash trees that are killed by dieback and that can safely be left standing to break down naturally will help increase our deadwood quantities in woodlands, with all the benefits that will bring.

Allowing natural processes in East Dartmoor’s woodland NNRs is one of Natural England's management response to Ash Dieback. In the Derbyshire Dales NNR, the ravine woodlands are set to be very badly affected by Ash Dieback. This forces a more active management approach here that includes widespread felling of ash to make plantable areas for key replacement species such as wych elm and lime. Management programmes for responding to Ash Dieback are site-specific and based upon the risk to the public (and those managing the sites) and the impact on the site. Allowing ash woods and stands time and space for natural regeneration could potentially mean re-routing or closing permissive footpaths on reserves in order to minimise the risk to the public and give nature space and time to deal with the disease.

The likely loss of 4 of every 5 ash trees will have a huge impact. There are, though, initial findings that point toward some of our ash being resistant to the disease, which should give us hope that our ash woodlands could recover, perhaps in an estimated 50 years. As part of Kew Garden’s UK Tree Seed Collecting Project, ash that exhibit tolerance to the fungus will be identified and their seed stored at the Millenium Seed Bank to facilitate research into the response and recovery of ash trees to Ash Dieback.

Field Officers from Kew assess an Ash

We are witness to a change in the role of the Common Ash in our woodlands, their airy canopies will no longer sway in the wind, dappled sunlight moving across their smooth bark. They are becoming prematurely veteranized: where it is safe to do so, they will stand as still monoliths, decaying as they continue to provide a home for other woodland organisms.

For more information on Ash Dieback see https://www.woodlandtrust.org.uk/trees-woods-and-wildlife/tree-pests-and-diseases/key-tree-pests-and-diseases/ash-dieback/

The Millennium Seed Bank https://www.kew.org/wakehurst/whats-at-wakehurst/millennium-seed-bank