In order to identify truly tolerant individuals, it is necessary to allow for at least 10 years of incessant infection pressure in affected trees. Before this time, trees may show a varying degree of tolerance, but most will eventually develop dieback symptoms and decline.It is important to retain ash stands until the few per cent truly tolerant trees stand out, so they can be selected for breeding.
Veteran ash trees (other than in-cycle pollards) should never be cut without an overwhelmingly good reason. Carrying out tree surgery puts the tree under stress. If the tree is susceptible to ash dieback the ‘pathway’ for the disease to the main stem is shortened when the tree has been cut. The new shoots are worst affected, making it difficult for the tree to recover from the intervention. By not undertaking surgery, some veteran ash might undergo very severe mechanical failure. However, ash can survive quite well after such a failure.
Re-pollarding previously neglected pollards (or veteran coppice stools) should not be undertaken as it can place too much stress on the tree when it is also under infection pressure.
Dead wood is an important resource in woodland ecology, and a proportion of dead wood ash should be retained (standing and fallen). If it is likely to impede woodland management, it can be moved, but should still be retained.