Ash Trees and Lichen {Pond Study: Week 9}

In this post we explore UK Ash trees and the Lichen that lives on it. At the beginning of this pond study we chose one tree to follow over the course of the year.

Find Out More! Read all about our plans for a year long pond study and all the fun activities we’ll be doing

Ash Trees and the Lichen it Supports

The UK ash tree (Fraxinus excelsior) is a common and important native tree. However, it is under severe threat from a fungal disease called ash dieback. There are an estimated 150 million ash trees in the UK, playing a significant role in woodlands, hedgerows, and parks. 

Read about our pond assessment here!

Identification

• Leaves: Ash leaves are compound. This means they are made up of 3 to 6 pairs of light green leaflets on either side of a central stalk, with a single leaflet at the end. They are often one of the last trees to grow leaves in spring. And one of the first to drop them in autumn, sometimes while they are still green.
• Buds: In winter, ash trees can be identified by their distinctive black, velvety buds. These are arranged in opposite pairs on the twigs.
• Bark: The bark is pale brown or grey and becomes fissured as the tree ages.
• Seeds: The seeds, known as “ash keys,” are winged and hang in bunches. They often stay on the tree well into winter. 

Catch Up! Take a quick read of our first post about the Ash Tree we chose to study this year

The Importance of Ash Trees to Wildlife

Ash trees are valuable habitats. They therefore support over 1,000 species of wildlife, including insects, birds, mammals, and lichens. The airy canopy of an ash tree allows sunlight to reach the woodland floor. This helps wildflowers like dog’s mercury and wild garlic to flourish.  However, the future of the UK ash tree is in serious doubt due to ash dieback which is caused by the fungus Hymenoscyphus fraxineus. 

• Origin and Spread: The Asian fungus, first appeared in the UK in 2012 and has since become widespread.
• Effects: The disease causes leaf loss, lesions on the bark, dieback in the crown. This can lead to the eventual death of the tree.
• Impact: It is predicted that the disease will kill the vast majority of UK ash trees, potentially reshaping the landscape forever.
• Hope for Survival: While most trees are highly susceptible, some appear to be resistant to the disease. Basically this offers a potential path for future research and repopulation. 

The Cultural Significance of Ash trees and its Uses

The ash tree has been historically significant in the UK: 

• Folklore: In Norse mythology, a mighty ash tree supported the universe. In the UK, it was once regarded as a healing tree.
• Timber: Ash timber is strong, flexible, and withstands shock well, making it ideal for tool handles, sporting equipment (such as hockey sticks and snooker cues), and furniture.
• Fuel: Ash wood burns well even when green, leading to the saying, “Ash wood wet and ash wood dry, a king can warm his slippers by”. 

We visited our pond for some pictures and to gather the bits and pieces we needed to do our activities at home:

Ash trees are a vital habitat for a huge variety of lichens in the UK, but this delicate ecosystem is currently threatened by ash dieback disease. The alkaline, or base-rich, bark of ash trees is ideal for many lichen species, with over 500 different types recorded on them. 

The importance of ash trees for lichens has increased in recent decades. This is because they provide a refuge for species that lost their habitat due to Dutch Elm Disease. 

Ash Dieback and its Effect on Lichens

Ash dieback is a fatal fungal disease caused by Hymenoscyphus fraxineus. The disease is causing the widespread loss of ash trees, which in turn threatens the diverse lichen population they support. 

• Rapid decline: As ash trees die, their bark and the lichens growing on it are lost, which could cause a significant decline in lichen diversity.
• Reduced resistance: Years of air pollution and acid rain have stressed lichen populations, making the loss of ash trees specifically—a key habitat for base-demanding species—a particularly severe threat.
• Conservation efforts: In response, lichen specialists are taking measures such as translocating rare species from infected ash trees to nearby, more resistant tree species like hazel. 

Common Lichens Found on Ash Trees

Ash trees in the UK host a wide range of lichens, from common species to those of international importance. Some notable examples include: 

• Xanthoria parietina (Common orange lichen): This foliose (leaf-like) lichen is highly tolerant of pollution and often appears as vibrant yellow or orange patches on a wide variety of surfaces, including ash bark.
• Lungwort lichens (Lobaria species): These leafy lichens were once widespread but are now largely confined to the humid, clean-air woodlands of the UK’s western regions. Species like Lobaria pulmonaria grow on ash and other deciduous trees.
• Ramalina farinacea (Shaggy strap lichen): This fruticose (shrub-like) lichen is commonly seen on the bark of trees and is one of many that finds a home on ash.
• Lobarion community: Ash trees, especially in humid western woodlands, support this internationally important group of lichens, which includes species like Lobaria pulmonaria and Sticta sylvatica. 

Firstly, we collected a small branch with a good amount of Lichen on it and went home.  On returning I had the children learn a bit more about the different types of lichen. We learnt that the type of Lichen present indicates the level of air pollution. 

We have also assessed the pond for all types of pollution in this post and took the investigations further by looking at all the pond water had to tell us.

Secondly, we studied the Lichen under a magnifying glass:

Lastly, we tried to identify the different types of lichen. Our branch contained two different Lichen (Xanthoria parietina and Lobarion) indicating that air pollution was very low. 

Read More! If you’d like to know more about the various types of fauna found around the pond, then you need to check out this post here.

The Ecological Role of Ash Lichen

Lichens on ash trees are not parasites; they do not harm the tree. Instead, they are an indicator of a healthy, biodiverse environment. 

• Habitat and food: Lichens provide shelter for small creatures like spiders and beetles and are a food source for moths.
• Increased biodiversity: Allowing lichens to grow on trees boosts local biodiversity, especially since many species are threatened by habitat loss and pollution. 

Isn’t nature just magnificent?

Our journal page for April is all about the ecosystem.  We made the tree out of our drawings and stuck dried on Lichen on the truck.  The rest was drawn or sketched and we added notes to remind us of the components of an ecosystem:

So enjoying our pond study!