The Twin Threats to the British Ash: A Biological Briefing
As we walk through the countryside of Portslade and Lancing, we are witnessing a landscape in transition. The ash tree, a keystone of the British environment, is currently facing a "pincer movement" from two very different biological adversaries.
I. Ash Dieback (The Fungal Disease)
Cause: The fungus Hymonoscyphus fraxineus (formerly Chalara fraxinea).
Ash dieback is no longer a distant threat; it is widespread across the UK.
How it Operates
The Spore Cycle: The fungus develops on infected leaf litter during the summer. Windborne spores then land on healthy ash leaves.
The Vascular Attack: The fungus penetrates the leaf and moves into the tree's vascular system, blocking the transport of water and nutrients.
The Symptoms: Look for wilting, blackening leaves, and "diamond-shaped" lesions on the bark. The crown begins to die from the tips inwards.
🌿 The 2026 Perspective: "New Hope"
There is a glimmer of hope in the latest research from June 2025. Scientists at Kew Gardens and Queen Mary University have found that new generations of wild ash are rapidly evolving natural resistance.
II. Emerald Ash Borer (The Insect Pest)
Cause: An invasive beetle (Agrilus planipennis).
While ash dieback is a disease, the Emerald Ash Borer (EAB) is a predatory insect. It is currently the "wildcard" of British forestry.
The Mechanism of Destruction
The Larvae: Unlike the fungus, the EAB kills through physical destruction. Its larvae chew "S-shaped" galleries into the inner bark, effectively girdling the tree.
7 The Fatal Signature: An infested tree is usually identified by D-shaped exit holes in the bark where the adult beetles emerge.
8
🚨 Current Status (January 2026)
As of this month, the Emerald Ash Borer remains officially absent from the UK, though it is moving steadily westward across Europe.
III. Key Differences at a Glance
| Feature | Ash Dieback | Emerald Ash Borer (EAB) |
| Type | Fungal Disease | Insect Pest (Beetle) |
| Origin | East Asia | East Asia |
| Status in UK | Widespread & Established | Absent (High Alert) |
| Primary Sign | Wilting leaves / Diamond lesions | D-shaped holes / S-shaped tunnels |
| Climate Link | Thrives in mild, wet winters | Spreads through imported firewood |
🔍 Spotter’s Guide: Ash Dieback vs. Emerald Ash Borer
When you are out in the Sussex woods this month, use this guide to distinguish between the established fungal disease and the potential new insect threat.
1. Look at the Bark (Signs of Attack)
| Ash Dieback (Fungal) | Emerald Ash Borer (Insect) |
| Diamond Lesions: Look for dark, sunken, diamond-shaped patches where a branch meets the main trunk. | D-Shaped Holes: Look for tiny (3mm) exit holes in the bark. They have one flat side and one curved side, like a capital 'D'. |
| Bark Discolouration: Young twigs may turn a dark, purplish-brown or olive colour instead of their healthy grey. | Serpentine Tunnels: If bark has flaked off, you will see "S-shaped" or zig-zag galleries etched into the wood. |
2. Look at the Canopy (Symptoms of Decline)
The "Clumping" Effect: In trees with Ash Dieback, you will often see "epicormic growth"—clusters of bushy new leaves growing from the main trunk or the base of the tree as it tries to survive the blockage in its upper branches.
The "Top-Down" Death: With Emerald Ash Borer, the thinning usually starts at the very tip of the crown and moves down systematically as the larvae girdle the tree from the top.
Woodpecker "Flecking": If you see bright, light-coloured patches where woodpeckers have stripped away the outer bark, it’s a sign they are hunting for larvae—a major clue for EAB.
3. The 2026 Local Context: Sussex Restoration
While the devastation is tragic, the work being done by the South Downs National Park and West Sussex County Council this year is focused on the future:
Safety Felling: You may see felling near roads and paths. This timber is often sent to the Kent Renewable Energy plant to be turned into green electricity.
The 5% Survivors: Experts believe about 5% of our native ash have high natural resistance. If you see a perfectly healthy, leafy Ash surrounded by dead ones, do not touch it! It might be a "Mother Tree" and should be reported to the Woodland Trust.
Author's Note: A Changing Heritage
The loss of the ash is more than just biological; it’s the loss of the wood used for tool handles, oars, and the spears of our Saxon ancestors (the "Saxon hair" from your previous poem!). By documenting these changes, we aren't just mourning a tree—we are recording a chapter of our natural history.
Why this belongs in the Archive
For a historian, the loss of the ash is a loss of a cultural landmark. Much like the Dutch Elm Disease that changed the face of the British countryside in the 1970s, these two biological threats are rewriting our local geography.
Documenting this now ensures we remember the "green" world as it was, even as we look for the resistant "Mother Trees" that will seed the forests of the future.
No comments:
Post a Comment