As you walk through the parks of Bourne you may or may not notice the lichen on trees, walls or even the floor. These scaly, warty, reptilian like marks seem to be on everything.
On the whole we seem not to just ignore them, but are almost oblivious to their existence. But spending a few moments looking at them can teach a lot about the health of our environment, not just for wildlife but for humans as well.
So what is a lichen?
Well it’s two forms of life living together; fungi and algae in a symbiotic relationship. One in five of all fungi can form these special attachments. Simply put, fine threads of fungi, called hyphae, ensnare algae to form a body called a thallus. Think of a thallus as a three layered sponge cake. The bottom part is fungus which stores water and allows air to circulate. The “filling” in the middle is the algae that produce sugars and then on top of that another layer of fungus which protects the algae below. Because of this a thallus is quite self-contained and has the ability to survive in some of the most hostile environments. From deserts to the arctic, lichen are found everywhere on Earth, including one lichen that lives in seawater.
The fungi element feeds off the sugar molecules photosynthesised by the algae. In return the fungus stores water which prevent the algae drying out. It protects the algae from dangerous ultraviolet light from the sun that would eventually break it down.
The fungus also produce antibiotic and anti-bacterial chemicals which indirectly benefit the algae.
Lichen absorbs ultraviolet light with interesting and surprising effects.
If we were to go outside and shine a UV light, as we can’t see in the ultraviolet spectrum naturally, on lichen at night in a park for example, you would be amazed at the variety of colours from day glow blues to reds to orange reflected at you. A park suddenly becomes psychedelic!
The reason is that they produce chemicals to protect themselves from the sun, which reflect light back in an array of colours as an interesting side effect. In fact they are so good at protection, that scientists are investigating them as a possible source of a natural sunscreen lotion for humans.
We use lichen too in other ways. Harris Tweed and Burberry fabrics have been coloured with a dye made from common rock lichen. The Roman Emperors used to dye their togas with a special purple extracted from lichen. In France, the Mousse de Chere lichen is used as a fixative in perfumery. They have been used in deodorants and laxatives.
Lichens are used to produce antibiotics for the pharmaceutical industry. Research into the chemical makeup of them suggests possible treatment in the fight against cancers and viral infections and even HIV.
Lichenometry was invented in the 1930’s as a way for geologists, scientists and archaeologists to date environments. Lichen can live for a very long time; one is thought to be over 4,000 years old.
Certain lichen species have predictable growth patterns. By measuring the diameter of lichen can tell how long a stone, for example, has been exposed to the elements. The age of a wall could be dated by when the lichen started to grow on it.
Lichens are also useful to the wider plant community. They help recycle nutrients and provide habitats for various spiders, mites and lice. There are even specialist insects that depend on them. The female of the lichen case bearer moth use bits of lichen to make a case in which to lay eggs in, for example.
However they are really useful for determining the health of the environment where we live in. Because they are totally dependent on their surroundings - as they can’t move around - for water, scientists can use them to work out how polluted an area is. Air pollution changes the acidity of water, which can kill if overly acidic. Up until the early 1970s sulphur dioxide was the worst pollutant. It was generated by coal powered industry and coal fires in the home. It killed off nearly all lichens in urban areas. Now with the advent of Clean Air Acts and more efficient energy, lichens are recolonising towns and cities again.
Today’s pollutants are nitrogen compounds from vehicles and intensive agriculture. Some lichens actually prefer nitrogen and spread because of it. Other species are killed off or are restricted in their growth.
By studying the different varieties of lichens and the number of them, scientists can work out how air pollution is affecting the air that we breathe. As a general guideline the more polluted an area is the smaller the number and variety of lichens will be found. So next time you are out and about stop and have a look at these little indicators – they are nature’s version of an early warning system.
Judging by the number and variety I found around town, Bourne seems to be reasonably healthy!