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News Anaylsis

By Roger Kent, Alan Simson, Colin Moore, Annabel Downs

Ash to ash

The initial surge of public interest in ash dieback has temporarily waned during the dormant season for the trees and fungus. By this summer we will have a better grasp not only of the pathology of the disease but also of the potential impact of ash dieback on our landscapes. The visual loss could be devastating.

n February this year the Forestry Commission confirmed the presence of the ash dieback fungus Chalara fraxinea in 19 nursery sites, 189 recently planted sites and 170 established woodlands, affecting most counties throughout the UK. The spread of the fungus, currently usually shown as dots on a map, will probably soon need a bigger symbol.

The National Environmental Research Council’s Countryside Survey, an audit started in 1978 (in the wake of Dutch elm disease), produced its latest review of the distribution of ash trees in the countryside in November 2012, revised in 2013. This audit, which covers small woodlands, individual trees and linear occurrences coincided approximately with the arrival of C. fraxinea in the UK. It shows that in small woodlands (<0.5ha), ash is the second most abundant tree species, after oak, and that it is more abundant in England than Scotland or Wales.

Outside woodlands there are estimated to be 2.2 million individual ash trees, with ash again the second most common species, although few of these are veteran trees. There are just short of 100,000km of ash hedgerows and lines of ash trees, with the majority occurring in England. The National Forestry Inventory Commission’s preliminary estimates for broadleaf species in British woodlands larger than 0.5ha (produced in December 2012), indicates that there are 126 million ash trees in these British woodlands, making ash the third most prevalent broadleaf species. Ash accounts for approximately 14% of the total standing volume of broadleaf trees in the UK, with the majority in private woodlands.

These figures make it clear that ash plays a prominent role in the landscape in terms of commercial forestry. It has an equally significant role environmentally in carbon capture and in ecology and conservation (with additional interest in the prospect of wider eco-benefits gained from all that decaying timber). The sheer quantity of ash trees in the landscape and their location, mean that they also have a significant cultural and visual presence.

What the facts and figures don’t reveal is the existence of locally significant ash trees, including all those urban and suburban places where ash trees grow and are important to our daily lives: as street trees, in squares where their light foliage provides a visual connection between surrounding buildings and the square itself, in public parks and gardens, in private back gardens, along railway lines where it is coppiced and self seeding, and as the dominant canopy tree in bluebell woods in the Midlands. The list of locally significant ash trees is endless and the loss of these trees will leave enormous gaps in our everyday landscapes.

The LI through its biosecurity sub committee is collaborating with a group of Government departments, agents and other organisations (DEFRA, Forestry Commission, Natural England, National and Woodland Trusts, Tree Council, HTA, FERA, AA and others) to share practical and technical information and advice and, using this information, the biosecurity group has prepared and updated specific guidance for landscape architects: see bit.ly/mXQMd9

The fungus Chalara fraxinea is here to stay: we can neither eradicate it nor halt its progress. We know that in Denmark it has spread very rapidly and affected approximately 95% of all the ash trees; in other areas where the fungus has long been present, the impact is far less; we do not yet know how swiftly it will run through UK or how many of our ash trees may prove resistant to the fungus.

It is one of a series of new or impending destructive diseases and pests to affect trees, plants and pockets in the UK. It is probable that these new pests arrived through a combination of factors, with imports of contaminated nursery stock and climate change repeatedly identified as the primary contributory factors.

Part of the work of the collaborative group will be to lobby for support and changing practices to minimise incoming diseases and pests, to find ways of making our existing flora and fauna more resilient, as well as promoting policies and strategies which facilitate replacement of ash trees lost as a result of C. fraxinea. Each of the participating organisations has different priorities and objectives. Broadly these can be categorised as commercial, ecological, and culturalaesthetic; and although there will be conflicting priorities expressed, the LI biosecurity group will ensure that the cultural and aesthetic aspects of the broader landscape are included in all the thinking and solutions.

Where ash has been used to screen old or more recent developments as part of planning control, we need to consider how to ensure the commitment to maintain screening that lasts for the life of the building, highway or other major development, and not simply to gain planning consent. If a tree is described as being grown in the UK, we need to know if this is for its entire life and not just the last season. We need to know what are the best trees to plant now.

The landscape profession has the vision and methodologies to provide insight into the significant visual changes which will be brought about as a result of this disease. We also aim to establish a photographic record of ash trees in the UK. The LI biosecurity group has its work cut out but it will keep you posted so we can all make the best decisions.
The authors are members of the LI biosecurity sub committee.

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