Golden lichens on south side of a staddle stone
Lichens are complex and fascinating, but once befriended can be used to help you navigate.
Lichens are a partnership between fungi and algae. The fungi forms the structure and the algae photosynthesizes (something the fungi cannot do on its own), producing sugars which the fungi is very grateful for. The way I like to think of this is that the fungi builds a house and then the algae lives there and brings in the money, in the form of sugars. It is a bit of a dream team, which may explain why lichens can claim to be some of the oldest living organisms on the planet, some even thought to have lived for 8,000 years.
Like all partnerships, lichens tend to thrive in conditions that are not ideally suited to either party succeeding on its own. If algae or fungi can get by well without the other half then this is what they tend to do. This is one reason why lichens are fussy about their location.
Another much more important factor in the location of lichens is that they use the minerals in the surface they grow on and are therefore very sensitive to surface types. Unlike mosses or algae, which tend to thrive wherever moisture is retained, lichens are fussy about bark and stone type. Each area has its typical surfaces, ie. its native trees and rocks with their associated minerals, and getting to know these is a part of getting to know lichen behaviour.
Lichens share with mosses a sensitivity to environmental conditions, but unlike mosses they do not have a universal preference for moisture. Many do like a consistently wet surface, but others like a dry one and some seem to prefer the combination of regular rain and some sunshine.
What does all of this mean for direction-finding? Well, putting all the pieces together, what this means is that by remaining aware of surface types in an area you will start to notice patterns. In England there is a rust-coloured lichen that likes beech trees, but it likes to stay moist and so can be found on the northern side of these trees ( – strictly speaking is an alga, called trentepohlia).
Like a lot of natural navigation clues, exposure is important, and so the effects tend to be more pronounced on isolated trees or at least ones that are not fully shielded from the southern arc of the sun. There is a lichen that is pale green with dark speckles that I found on the southwestern side of beech trees too, most likely it is enjoying the rain-bearing winds from the southwest, but does not mind a bit of sun too.
On stones, whether in the wilderness or in a town, it is common to find mosses on the northern side and golden coloured lichens on the southern side. There are few rules that can be applied across the board to lichens, this is part of the satisfaction of building up local knowledge, but one that has worked for me is as follows: if a lichen has a golden appearance then it is more likely to be on the southern side than any other. A good way to remember this is by thinking of it sharing the gold of the sun.
Using lichens for natural navigation is challenging and at times it can be frustrating, but it is worth remembering that lichens are very sensitive to air quality, so even if they fail to form a perfect compass for you, they can at least assure you that you are breathing fresh air.
In my books I cover the navigational use of lichens, mosses, the sun, moon, stars, plants, animals, buildings and weather in more detail.