Ash dieback has become one of the defining stories of our treescape in recent years. If you walk through woodland in Sussex and notice thinning canopies, brittle branches, or young trees failing to thrive, you are likely seeing its impact. Studies suggest that 80% of ash trees will be lost to ash dieback across the UK at a cost of billions. But what is it?
The science
Ash dieback is caused by a fungus called Hymenoscyphus fraxineus. It originated in Asia, where native ash species evolved alongside it and developed resistance. Our European ash, Fraxinus excelsior, did not. The fungus was first identified in the UK in 2012 and since then, it has spread widely. The spores are microscopic and remarkably mobile, travelling miles on air currents before settling on leaves and stems.
The fungus infects ash leaves during the growing season. From there, it grows into the leaf stalk and then into the tree’s circulation system, blocking the flow of water and nutrients. Lesions form where branches meet the trunk, and over time the crown begins to thin and die back. Some trees succumb quickly. Others hold on for years, producing epicormic growth, those tufts of leaves sprouting from the trunk in a last attempt to photosynthesise.
In Sussex, ash is not a marginal species. It is woven into our hedgerows, lining rural lanes, shaping woodlands and sheltering wildlife. Ash supports hundreds of species, from lichens to insects to birds. Its loss affects light levels, soil moisture and habitat structure. In places like Lancing Ring and across Adur and Worthing, we are already seeing the impact, with mature trees becoming unsafe and young regeneration struggling.
So what can be done?
There is, at present, no cure. However, not all ash trees die. A small percentage show natural tolerance. These survivors are vitally important. Research programmes like the one at Wakehurst are identifying and propagating tolerant stock, offering hope for future resilience. In the meantime, management focuses on safety, selective felling of dangerous trees, and replanting with a diverse mix of native species to ensure our woodlands remain ecologically rich.
Tree action volunteers planting new trees in Lancing Ring Woodland to replace trees lost to ash dieback
Here in Sussex, our response has been practical and hopeful. Working with local councils and volunteers, we have been replacing lost ash with a thoughtful variety of species suited to our soils and climate. Most recently, Tree Action was part of an initiative with Adur and Worthing Council to plant 2000 trees to replace those lost to ash dieback in the Lancing Ring Woodland. We planted oak, field maple, hornbeam, and others to help build a more varied canopy for the decades ahead. This calculated diversity is not just an aesthetic choice, it is a form of protection itself: A woodland with many species is less vulnerable to a single pest or pathogen in the future.
Ash dieback is a reminder that our landscapes are living systems, shaped by global trade, climate and time. It is also a reminder that stewardship matters. By planting wisely, monitoring and nurturing resilient woodlands we are shaping the next chapter of our countryside.