Being a coastal region, Brittany is a natural home for these orange Xanthoria lichens, which can be both a blessing and curse when it comes to using them to understand direction. This is because conditions need to be close to perfect for lichens to thrive, but if they are too good then a lichen will manage well on more than one side, and occasionally on all sides.

This nuance creates a challenge for those new to the subject of natural navigation, including those who took part in the upcoming BBC2 series, ‘All Roads Lead Home’. Sue Perkins, in particular, was understandably frustrated that the lichens would not always obey a perfect rule in terms of the aspect they preferred. In the very short time available, it was incredibly difficult to convey the rich way lichens can help us navigate.

The important point is that lichens do not care about our concepts of north, south, east or west, they care only about their environment. South-facing walls, rocks and bark will tend to be drier as they receive more direct sunlight than north-facing ones (in the northern hemisphere). These sunny, dry conditions are ideal for these orange lichens and so there is a strong correlation between orange lichens and south-facing, but, and it is a big but, the keys lie in patterns and assymetry.

It takes time and patience to appreciate that hard rules are pointless when it comes to lichens, as lichens are as mischievious as they are fascinating: rules will deprive us of both confidence in direction and a richer understanding of our environment.

It is only by spotting patterns, getting to know consistencies – and indeed inconsistencies – that we grow to understand the habits, ie. habitats, of the lichens in each area.

Close to the sea these orange Xanthoria lichens are often happy to cover all sides of the right types of rock, but further inland they can be fussier, showing a marked preference for the sunnier southern side. Further inland still, they become rarer altogether. But they will tell a story of environment in each place, one that is fun to read, providing you resist the temptation to jump to the final page of the story by assuming rules and tricks that are not part of the plot!

In this picture we are looking east in Ballycroy National Park. Notice how the two sides of this drainage ditch look very different. The darker left side of the ditch, that is the south-facing northern side, is covered in a thick mat of heather, whereas there is little or none growing on the opposite bank. Heather dislikes shady spots and so can be a good indicator of south-facing inclines in northern latitudes.

Assymetry, my friends, that is the name of the natural navigation business!

The two pictures above show two sides of the same bridleway signpost on the South Downs Way. The arrows both point east and there is a clue to this in the photos. It is not in the lichen growth, which unusually is quite similar on both sides, but in the colour of the arrows themselves. The blue of the south-facing (but east-pointing!) arrow has been bleached more by the sun. The three main weathering clues are sun, wind and rain. The first will usually be greatest on the southern side, but wind and rain will usually leave their marks more prominently on the southwestern side.

The crop tends to be on a field that will get a good amount of sunlight anyway, often south-facing, but even within the fields there are subtle shade differences. The flowers tend to appear first in the south-facing dips in the land. This is probably because they are getting plenty of sun, but being sheltered from the cooling winds. As a general rule, nature moves faster the warmer things are.

This primrose, the only one in the area, was unsurprisingly in a south-facing spot. The thick bed of south-facing moss that surrounds it on the beech roots should not surprise us. Moss grows in abundance close to the ground where moisture levels remain generally high, even in south-facing places.

The technique of trail blazing, marking trees to show others the way is ancient, but the chalk markings on this beech tree were a little disconcerting. Apologies, the picture is out of focus as I was hurrying to catch up with others, but hopefully you can make out the following: arrows showing the way, the words, ‘Tom’ and ‘This Way’ and a picture of a sad, perhaps perplexed or even angry face. Hopefully Tom is less sad now, having spotted these blazes and been reunited with his kin. He will no doubt have been sped on his way to that reunion by noting that the morning sun’s shadow meant that the arrows were pointing south north. (Thanks to Shane for spotting my deliberate error on that one!)

… however, this is a risky business, so here are two jalapeno chillies. One lived its life in a south-facing greenhouse, the other lived near it, outside near a south-facing wall. They both received identical amounts of sunlight. They both grew in the same soil and received plenty of water. The only serious differences to their environments were the temperature and wind exposure.

It is not too hard to see that nature is quite fussy about its environment and it is this fussiness that can give us a helping hand. It is sometimes possible to deduce useful things about the elements from two examples of the same species. One big example of this can sometimes be found in the different look and feel of two sides of the same hill or mountain.