Ash Dieback, caused by the fungus Hymenocyphus fraxineus, appears to have been introduced into Europe from East Asia probably on imported trees infected with the disease. First reports came from Poland in the early 1990’s. It was discovered in England on a batch of trees imported from Holland in 2012, and by October of that year further cases had been found in Norfolk. In October 2013 infected trees had been found in South Wales. The disease has moved quickly across the UK partly through wind spread of the fungal spores but also by transplanting infected trees. The first case was recorded in the Mendips in 2015 and is now visible throughout the area. Somerset County Council suggest that 90% of our ash trees are likely to die.
The most comprehensive account of the nature of ash dieback and its implications can be found in the toolkit published by the Tree Council. It includes guidance on how to identify the disease and recommendations for landowners and public authorities.
Trees affected by ash dieback may be weakened inside without that being obvious externally as shown in the picture below. This can make dealing with them risky
This is a general article about dieback highlighting its impact in the South West and its implications for the landscape and ecology.
The Westbury tree group has produced a simple summary of advice in the form of frequently asked questions and answers here
The Devon Ash Dieback Resilience Forum has produced advice on suitable replacements for ash. No one tree can replace all the ecosystem functions of ash and a mixture of native trees like oak, alder, aspen, sycamore, mountain ash, birch, hornbeam, field maple and elm is recommended. Note however that the report is written for Devon – there is no equivalent guide specific to Somerset.
It is important to look at what else is growing near by as a guide to what might grow well as conditions vary. Your choice would be different on the levels where willow could grow well but might struggle on the dry scarp slope. It is essential to grow a variety of different species both to insure against new disease damage and to help the many invertebrates and plants that are being orphaned by the loss of ash trees.