Fairy ring


 * For the article dedicated to the Southwest African phenomenon of fairy circles, see here.
 * For the soundtrack by Mike Roland, see here.



A fairy ring, also known as fairy circle, elf circle or pixie ring, is a naturally occurring ring or arc of mushrooms. The rings may grow over ten meters in diameter and become stable over time as the fungus grows and seeks food underground. They are found mainly in forested areas, but also appear in grasslands or rangelands. Fairy rings are not only detectable by sporocarps in rings or arcs, but also by a necrotic zone (death grass) or a ring of dark green grass. If these manifestations are visible a fairy fungus mycelium is likely present in the ring or arc underneath.

Genesis
There are two theories regarding the process involved in creating fairy rings. One states that fairy ring is begun by a spore from the sporocarpus. Initially the spore lands on suitable ground, and as it starts to grow underground it pushes out mycelium (fungal threads) in all directions. As the mass of mycelium grows the central part dies off, leaving a ring of mycelium growing at the outer edge. Eventually, when season and weather allow, mushrooms are produced above the mycelium and release spores. Sometimes, several years may go by before mushrooms appear around a fairy ring. The underground presence of the fungus can also cause withering or varying colour or growth of the grass above. Many fairy rings are believed to be coenocytic, meaning that an entire ring is just one large cell with multiple nuclei.

The second theory, which is presented in the investigations of Japanese scientists on the Tricholoma matsutake species, shows that fairy rings could be established by connecting neighbouring oval genets of these mushrooms. If they make an arc or a ring, they continuously grow about the center of this object.

It is said that there are about 40 to 60 mushroom species which can grow in the fairy ring pattern. The best known is the edible Scotch bonnet (Marasmius oreades), which is commonly known as a "fairy ring mushroom".

Necrotic or rapid growth zones
One of the three manifestations is a necrotic zone, or area in which grass or other plant life has withered or died. These are caused by the mycelia, which during a very dry year coat the roots of grasses and other herbs in meadows. After some time they are removed by biotic factors from the ground, at which stage we can see a zone on the surface soil. Patterns other than the basic ring or arc are also possible: circles, doubled arcs, sickle-shaped arcs, and other complicated formations are also formed by this process. Fungi can deplete the soil of readily available nutrients like nitrogen, causing plant growing within the circle to be stressed which leads to plant discoloration. Some fungi also produce chemicals that act like hormones called gibberellins, which affects plant growth, causing rapid luxuriant growth.

Types
There are two generally recognised types of fairy ring fungus. Those found in the woods are called tethered, because they are formed by mycorrhizal fungi living in commensalism with trees. Meadow fairy rings are called free, because they are not connected with other organisms. These mushrooms are saprophytic. The effects on the grass depend on the type of fungus that is growing; when Calvatia cyathiformis is growing in the area grass will grow more abundantly; however, Clitocybe gigantea will cause the grass to wither.

Fairy rings in folktales and mythology
In English folklore, fairy rings were said to be caused by elves, fairies or pixies dancing in a circle, wearing down the grass beneath their feet. Toads would then sit on the mushrooms, poisoning them; hence the name toadstool. In Sussex they were called, “hag tracks”, in Devon people thought that fairies caught young horses and rode them in circles.

In Scandinavian folklore, these circles were attributed to elves or witches and were called älvdanser, i.e. elf dances, älvringar, or heksering.

In German-speaking Europe, fairy rings are known as Hexenringe, or "witches' rings", stemming from an old medieval belief that the rings represented places where witches would have their gatherings. In Austria people thought that dragons' breath burned  the land. Similar myths to those in German folklore can be found in Czech, Slovak, Polish and even Russian folktales. In the Czech language they are called čarodějné kruhy, as they are thought to have been caused by a dragon's having a rest at those places.

Another myth states that fairy rings are doors into the fairies' world, transporting people to other places or making people appear in the same place in a different time. Young ladies are also warned not to touch the dew on the grass within the ring, as it is believed that it can cause skin problems.

Trivia

 * The MMORPG RuneScape features a magical fairy ring network used for transportation.
 * Mushroom circles can be found in several locations throughout the world in the MMORPG, Ultima Online.
 * One of the largest rings ever found is in France. It is thought to be about 800 m in diameter and over 700 years old.

"Crop marks"
Not long after World War II, the aerial surveys that were being made over large areas of Britain revealed some unexpected phenomena, undetectable from the ground. When the surveys photographed ripening crops or drought-stressed terrain they revealed what were soon termed "crop marks", the differential ripening of the crop that revealed differences in the subsoil. These patterns were found to be caused by the buried remnants of ancient buildings.

Linear crop marks
Linear marks in fields carrying crops are called trods in the West of England. It is not clear what causes this phenomenon, characterised as it by a darker hue of green than the crop either side.