Going, Going… not gone yet - Part 2

Factors To Consider In The Development Of A Proportionate Response To Ash Dieback Disease
This is the second in a two-part series focusing on the impacts of Ash Dieback Disease (ADD). Part 11 described the disease itself, it’s prevalence and how to spot symptoms. In this article, I’ll consider formulation of a proportionate response based on the Tree Council’s Ash Dieback Toolkit2. Since Step 1 (Awareness) was addressed previously, this article begins at Step 2 (Planning).

Planning

ADD is a serious tree health condition that will affect nearly all communities across the UK. Asset managers need to formulate a proportionate response that balances risk, budgetary pressures, community concerns and environmental impacts. Adoption of a proactive stance is likely to lead to better outcomes and reduced financial burdens compared to a purely reactive approach. Whilst the window for planning is closing, there’s still time to take effective action.

Planning needs to start with an assessment of the scale, current prevalence and risks associated with ADD in your communities. ‘Risks’ can encompass safety hazards, interruptions to communication and infrastructure, impacts on budgets and economic activity, additional pressures on certain industry sectors, reputational standing, community dynamics and disruption of natural ecosystems. Assessment can include the likelihood, magnitude and target (communities, people, property, etc.) of impacts. Since species of ash give rise to many of our most important amenity trees community engagement at an early stage is vital. Other considerations might include the presence of statutory tree protections (Tree Preservation Orders, Conservation Areas, Forestry Act 1967), the presence of particular species or habitats (Wildlife and Countryside Act 1981, The Conservation of Habitats and Species Regulations 2017, The Environment (Wales) Act 2016) or the presence of other regulatory designations (e.g. Scheduled Ancient Monuments, National Nature Reserves, etc.). Investigation during the planning stage can avoid delays later should an emergency response be required.

Action

Currently, there are no cures for ADD3. Its widespread prevalence and ability to spread rapidly by wind dispersal makes creation of ‘Protected Areas’ unrealistic. Large-scale removal of leaf litter is only likely to be of benefit for specific trees in well-tended parks and gardens. The import and movement of ash saplings has been banned since 2012 but internal movement of logs, bark and leaves may still take place. Large-scale application of fungicides would have obvious detrimental effects on the environment but some positive results have been reported with deep soil injection of biochar to selected trees. Overall, our best hope is to find, propagate and distribute resistant trees to restore our native treescape and much research is focussed on this.

It’s important to recognise that infected and even dead trees are still of considerable value.  Mortality across the UK is expected to be around 80% with some mature trees able to tolerate the disease for several years prior to death. Other trees have been observed to recover while around 1-5% may be fully resistant. Genetic markers have been identified raising the possibility that resistance is heritable so these remaining trees could be vital for our recovery from ADD4. Dead trees can provide a number of unique habitats making their retention in low-risk areas desirable. Advice from DEFRA3, Forestry Commission England5 and Natural Resources Wales6 all stress the need to avoid wholesale, indiscriminate felling of healthy or diseased trees and favour phased, risk-based approaches that allow time for communities, the environment and industries to adapt.

Effective communication

Effective communication with your communities is extremely important. The local population can be your eyes-and-ears on the ground and may be able to take action to preserve specific trees of high value. In the early stages of infection, nothing other than an increased frequency of tree inspection may be required. Inspections should include an assessment of the presence of basal lesions which appear to be associated with organisms of greater importance to tree stability such as Armillaria (Honey fungus). As trees move into disease stages 2 and 3, intervention may be needed which may entail pruning, deadwood management, specialist investigations or removal, depending on risk assessment. At stage 4, options may involve removal, retention or other crown treatments to eliminate risk but still preserve ecological benefits where possible. At all times, measures should be adopted to promote biosecurity, particularly by forestry and arboricultural professionals.

Recovery

The ultimate goal has to be restoration of ash trees in the UK treescape in the post-ADD environment.  For this, the disease resistant planting stock I referred to earlier will be required. In the meantime, the place of ash in UK ecosystems has to be filled for the sake of the 995 species associated with it8. This event also provides us with an opportunity to increase tree diversity and climate change resilience by planting species better suited to a warming climate.

In more natural settings, where replacement of ecosystem services is important, species selection must be made carefully. While a certain proportion of exotic species may be desirable, the focus must be on native and non-native species that can be a home to those organisms displaced from the dwindling ash population. To assist woodland managers with these selections a Research Note has been produced by the Forestry Commission9.

For amenity planting, trees with similar overall appearance and properties10 might include Tree of Heaven (Ailanthus altissima), Common walnut (Juglans regia), Chinese cedar (Toona sinensis) and Caucasian wingnut (Pterocarya fraxinifolia). These species are associated with warmer climates and have the potential to improve our climate resilience.

Concluding Comments
ADD is a complex, multi-faceted problem that has the potential to significantly disrupt our communities. We are well-placed to manage the situation with a large amount of in-depth research and advice available.  If the opportunity is taken, then we can use this event to make positive changes to the UK tree stock.

References

  1. Wilson, R. (2019). The Clerk Magazine, 50 (5), 50-51.
  2. Stokes. J. & Jones, G. (2019). Ash Dieback: An Action Plan Toolkit. Tree Council, London.https://treecouncil.org.uk/What-We-Do/Ash-Dieback
  3. DEFRA (2013). Chalara Management Plan (updated April 2019).
  4. Harper, A. et al. (2016). Science Reports 6, 19335.
  5. Forestry Commission (2019). Managing ash dieback in England.
  6. Natural Resources Wales (2017). Chalara Dieback of Ash Leaflet.
  7. Cox, S. & Roberts, J. (2018). AAGN2: The Application of Biosecurity in Arboriculture. Arboricultural Association, Stonehouse.
  8. Mitchell, R. et al. (2014). Assessing and addressing the impacts of ash dieback on UK woodlands and trees of conservation importance (Phase 2) (NECR151). Natural England, Peterborough.
  9. Broome A. & Mitchell, R. (2017). FCRN029: Ecological impacts of ash dieback and mitigation methods. Forestry Commission, Edinburgh.
  10. Johnson, O. & Moore, D. (2004). Collins Tree Guide. HarperCollins, London.

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