Stories from the Barn

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The Beauty of Lichen on Trees

Lichen on tree bark

Take time to look at lichen on tree trunks this Winter.

As the leaves fall from the trees it is a good opportunity to look at the lichen growing on the trunks of trees such as Hawthorn. The lichens seem to be full of colour and vigour at a time when little else seems to be growing. Many of these lichens are the crust forming sort and provide splashes of bright yellow, orange and green.

Sometimes the lichen seems to be wrapped around the entire branch or twig of a tree. It’s as if someone has dipped their brush into a lichen paint pot and set to creating a painting on the tree.

Now is a perfect time to go on a lichen hunt and check out the health of your local trees and acosystem.

What is lichen?

Lichen is perhaps one of our strangest organisms as it is not one single entity but a symbiotic relationship between a fungus and an alga or a cyanobacterium. Cyanobacterium are a group of photosynthetic bacteria, some of which are nitrogen-fixing. Lichen is not a plant although it does photosynthesize and this is the key to the relationship. Fungi cannot photosynthesize, that is use light energy from the sun to generate carbohydrates. So they have to find some other way outside of their own system to generate food. The fungi forms a relationship with an alga or cyanobacterium to form a lichen and thus has created a source of nourishment for itself. In effect the fungi is farming nutrients through this relationship.

Lichen on tree bark

Lichens are everywhere.

Lichens do not just grow on trees. They grow on rocks, fences, roofs, park benches, on just about every object. An ability to exploit all temperature zones, they grow in the coldest regions of planet Earth to the hottest. Lichens are thought to be amongst the longest living organisms and highly successful. There are over 20,000 species of lichens worldwide.


Lichen grows on so many things.

Do lichens growing on trees mean the tree is dying?

The lichen does not harm the tree and will not cause it to die. It can however be an indicator that the tree is ageing or that the environment is putting the tree under pressure. For example a tree in drought conditions may be more vulnerable to having lichen on the trunk.

Lichens as pollution indicators.

Lichens are well known for being pollution watchdogs. Where there is a high sulphur dioxide content in the atmosphere, lichens struggle to survive. However other lichens are very tolerant of high levels of nitrogen dioxide so in the countryside where farmers are using fertilizers, there is an increase in lichen growth. The yellow lichen splodges in our hedgerows are an indicator of too much nitrogen dioxide, pollution from agricultural fertilizer use.

Lichens as pollution indicators

There are many different colours and forms of lichen.

Saving rare lichens.

The National Trust has discovered a rare lichen on a fallen oak tree in an area of ancient woodland in Borrowdale in the Lake DIstrict. The lungwort lichen (Lobaria pumonaria) is found in ancient wildwood and is an indicator of a healthy woodland. However with increased levels of pollution it has become rarer, limited in amount and extent. The flourishing community on the fallen oak would die if left. Therefore it has been carefully removed and redistributed on about one hundred carefully selected trees in Borrowdale. This part of the Lake District is uniquely favoured by the lichen because of the high rainfall. Previous attempts at redistributing the lichen have had only a 1% success rate but the hope is that this larger translocation will have more chance of success.

The Press Release from the National Trust is available here