Lichens

Lichens in Sheepfield Copse

These are densely packed crustose lichens, on the bark of a young birch tree in Sheepfield Copse. Groups of lichen species are often consistently associated together, forming recognisable communities. It is probable this is a community of several species of Arthonia, specialists in smooth barked trees.

A lichen is not an individual organism; it is an association between a fungus and an alga and/or a cyanobacterium. In about 90% of all lichens, the association is with green algae that contain the pigment chlorophyll. This means that the alga can photosynthesise, producing energy-rich carbohydrates.

Lichens are a mutualistic associations: the algae and cyanobacteria benefit from the fungal structure, which protects them and holds them out in the air and the light where they can photosynthesise; the fungi, which do not photosynthesise because they do not contain chlorophyll, feed on the sugars produced by its symbionts. Both benefit.

Other species of lichen on other trees in the reserve – and a map where X marks Sheepfield Copse

Each part of a lichen, the fungus, the alga or the cyanobacterium can exist alone, but if they are living alone, they are not the same as they are when combined in a lichen. Growing individually: their growth, structure and biochemistry all have very different properties than those of the symbiosis.

A lichen is given the same scientific name as the fungus that makes up part of it, not the the name of the species of alga or cyanobacterium. And, by convention a lichen is always called a species although it might be more precise to call it an organisation of several species. The more we learn about our damaged planet and the things we share it with, the more clearly we can see the complex relationships between species – and how little we really know about them.

Next time you walk through the copse in Sheepfield, pause for a closer look at the trunks of the birch trees there.