Ash
BAW has a monoculture of predominantly Common Ash (Fraxinus excelsior). Tall stands of previously coppiced stools, over 300 years old, with multiple 2-4 trunks rising from those legacy stools:
- Average age of mature trunks over 80 years, 2-metre girth, and an average of 10-15 metres height.
- Excurrent growth indicative of high forest canopy seeking upper story sunlight; a system of branching in which there is a well-defined tall, slender central main stem, bearing branches which are limited in their length, diameter, and secondary branching:
- forming a closed woodland canopy, with bare trunks rising 10 metres to small tight crowns
- left alone, trees are unlikely and unable to simply fall over because of adjacent healthy trees and only likely to drop smaller dead branches, over time, into the adjacent tree canopy and undergrowth away from the main path (Falling within 2-4 metres radius of the trunk).
Ash Dieback
Ash dieback (Hymenoscyphus fraxineus also known as Chalara fraxinea), is the most significant tree disease to affect the UK since Dutch elm disease:
- It will lead to the decline and death of many ash trees in Britain and has the potential to infect more than two billion ash trees (over 1.8 billion saplings and seedlings to more than 150 million mature trees) across the country.
- Arriving in mainland Europe from Asia in the 1990’s Chalara has spread throughout Europe devastating up to 95% of trees, some showing a natural resilience. It was first recorded in the UK in Buckinghamshire in 2012, evidence suggests that it has been present since perhaps a decade earlier.
- The disease is spread by the wind through spores produced from fungal fruiting bodies on fallen leaves, once infected the fungus destroys the trees vascular system preventing nutrients and water movement. Once weakened the trees are susceptible to secondary pathogens like honey fungus (Armillaria )
- Symptoms of the disease are lesions on the bark, blackening of leaves, dieback of branches and whole tree death. Where trees are badly infected, they can develop decay and rot at the branches or root and stem base rendering the branches or whole trees unstable.
- When dismantling or felling diseased trees experience has shown that there is a propensity for the stems and branches to shatter “like a grenade”. This will determine the removal methods required in each scenario. Trees can become infected and can decline rapidly dependant on biotic factors, some trees can die within a couple of years where others may decline more slowly.
Figure 1 below is taken from the Tree Council’s Ash Dieback toolkit[1]. It provides a system for categorising the condition of trees affected by the disease and can be used by anyone responsible for woodland management to monitor the disease progression over time in individual trees.
Each surveyed ash tree can be assigned to one of the following four Ash Health Classes:
[1] Stokes.J., and Jones, G. (2019). Ash Dieback: An action plan toolkit
For detailed information about the progression of Ash DieBack please see the presentation made by Iben Margrethe Thomsen (a tree disease specialist from Copenhagen University):