Ash downfall

Here’s a Cramp Ball. There are hundreds of them here. They love dead or dying Ash trees.

I’ve been taking morning walks in a small woodland in Somerset and have noticed large areas of dead trees. I keep expecting them to burst into leaf, but they never will. They were Ash trees. They are all dead.

The widespread death of Ash trees in Britain is mainly due to the fungal disease Ash Dieback (caused by the fungal pathogen Hymenoscyphus fraxineus). It is likely to have significant and long-lasting effects on British wildlife. What will our woodlands look like in the future? Will there be significant changes? Will our habitats be less diverse?

The main ecological impacts are:

Loss of Habitat

Around 1,000 species are associated with Ash trees, and about 100 of these rely on Ash as their main habitat or food source. This includes lichens, fungi, mosses, and invertebrates. Some species are Ash specialists, such as rare Mycena fungi, and some types of beetle, and they may decline or face local extinction.

Impact on the structure of woodland

Ash is a canopy species of tree. Its loss alters light levels and the microclimate underneath. More light reaches the forest floor, changing understorey vegetation and potentially benefiting light-loving species. What will their loss do to native Bluebells, Lesser Celandine, and Bear’s Garlic? Changes in moisture and temperature levels affect soil life, fungi, and ground-dwelling creatures. Ash often grows in mixed woodlands, so the death of Ash may shift the habitat toward species like Sycamore or Beech, changing the features of the woodland.

Disruption of food chains

Many insects feed on ash leaves or live in its bark. Their decline affects the birds and bats that feed on them. Numerous fungi form intimate underground symbiotic relationships with Ash roots. These fungi contribute to the health of the soil and cycling of nutrients and many are specialists which can’t switch to other trees.

Opportunities for Invasive Species

Gaps left where living Ash trees used to be might be colonised by invasive species or non-native plants (like Rhododendron species or Himalayan Balsam), which may further reduce native biodiversity. The Himalayan Balsam is already spreading here.

Temporary changes

There may be many temporary changes different from the final ecological outcome. There may be spectacular blooming of insects and fungi associated with dead wood and the birds which feed on insects which feed on dead wood, or nest in dead trees.

There may be many Cramp Balls here now, but will Ash recolonise this woodland so there are many more Cramp Balls in the future?