Some of the woodlands in this part of Wales are classified as ‘temperate rain forest’, which isn’t some tabloid terminology but part of a formal classification of the planet’s habitats. These forests are globally scarce, found only in high-rainfall temperate regions; characteristically they have an abundance of epiphytic plants – in our case mosses, lichens and ferns.

I have been investigating a local wood which, although dominated by birch and rowan rather than the usual oaks, looks to me like one of these ‘Atlantic’ woodlands – not least because it is smothered from boulder to twig in a luxuriant coating of mosses and lichens. As I don’t know much about either of these I persuaded Dave Lamacraft, who is Plantlife’s lichen expert in Wales, to come and have a look. It was an education.

It turns out that lichenology is a bit like alchemy and is best taken slowly; which suits this place as it is a steep jumble of boulders discreetly draped in moss, just waiting to break your leg. Two things about lichens stand out: many of them are very small and all of them, until recently, were only referred to by Latin names. At least now there are some with English names, which helps a bit. Watching how Dave went about identifying them was fascinating; most have to be examined through a hand lens, which you hold to your eye and then lower to the plant, consequently you spend hours with your nose up against a branch or a boulder. Close up these lichens come in many forms: flaky, cupped, crenulated, fissured and strap-like; some were encrusted, others slapped on like face cream or pats of cold porridge. Some of those we found were easy to identify e.g. the fishbone beard lichen (Usnea filipendula), which hangs down like a hank of grey hair; or the barnacle lichen (Thelotrema lepadinum) whose fruiting bodies do look remarkably like barnacles. But many others were difficult, which is where the alchemy comes in – Dave variously shone an ultra violet light as some species show up a different colour or dabbed them with bleach for the same reason, he even chewed fragments – “if this tastes really horrible I will know which one it is!” More often than not he cut off a tiny piece, carefully folded it in paper, and stowed it in a collecting tin for later identification under the microscope.

There is a group of lichens known as ‘Atlantic’ species, which are characteristic of these high-rainfall west coast woodlands. Due to the scarcity of their habitat they are some of the most treasured of our lichen world and we have a particular duty to care for them. I had a hunch that this wood contained some of these and by the end of the afternoon, much to my delight, Dave had found a good selection of them. He also found several others which are indicators of long continuity, which supports the idea that this is a very old wood, perhaps a direct descendent of the original post-glacial ‘wildwood’.

As we walked back to the car Dave stopped to examine the old hawthorns and birch trees scattered across the pastures on the farm. He was looking for ‘nitrophilous’ species of lichen i.e. those that are indicators of a nitrogen polluted environment. Despite this valley having some of the cleanest air in England and Wales he did find some – just scraps – but they were there, where the rain and wind sweeps in from the west bringing nitrogen dioxide in solution. One of these lichens Xanthoria parietina, a conspicuous chrome-yellow crusty species, is sometimes common along main roads and at service stations just because it thrives on the nitrogen from exhaust fumes. It seems odd that we should have this pollution here when there is so little industry and settlement to the west, where the prevailing winds blow from, but it seems that exhaust fumes from cars and trucks and even offshore shipping are enough to push atmospheric nitrogen over a critical threshold. One consequence of this is that vigorous plants such as hogweed and stinging nettles, which thrive on nitrogen ‘enrichment’, are outcompeting more delicate plants such as violets and primroses, which prefer it nutrient ‘poor’. According to a recent Plantlife report this process is having a profound and detrimental effect on wild flowers and vegetation all across Britain.  It is raining fertilizer – and there are bound to be consequences.

Xanthoria parietina