A Celtic Rainforest: field trip to Glen Gallain

Seil Natural History Group is not long back from a recording field trip in Glen Gallain – between Kilninver and Kilmelford.  Despite the frosty conditions, 10 people made the trip – and as a general rule everyone is welcome to join these monthly outings.

The object of our visit was a mixed wood of hazel and birch with some ash.  Fortunately for us it was on a south-facing slope bathed in sunshine which had melted most of the snow, while on the opposite bank the ground was white and conditions a lot more gloomy.  The picture above shows the two sides of the valley, with the ice-covered River Gallain in the dip.

The hazel was of particular interest owing to the rich lichen flora that thrives in Scottish west coast hazelwoods.  These woods are of international importance and contain many lichens that are rare on a world scale.  The lichens, together with abundant mosses and liverworts, are able to flourish in this ‘Celtic Rainforest’. Here is the pollution-free air and the humid conditions they need, resulting from a wet climate with mild winters and cool summers. (Here is a good article on Atlantic hazelwoods).

The weather had been exceptionally cold and dry for some time and many of the lichens had a paler appearance than normal.  They soon recover their colours after a spot of rain.

Hazel continually puts up new shoots from its base, and these are initially colonised by thin crustose lichens which wrap around the bark and are hardly noticeable unless you’re looking for them.  In a good Atlantic hazelwood, the young stems are completely covered with these crustose lichens, and there is no bare bark to be seen.

The left-hand picture (Pyrenula occidentalis) shows the map effect formed by the various crustose lichens on a young hazel stem, with dark borders where two lichens meet.  The one with black bobbles (perithecia) on an orange-brown background is Pyrenula occidentalis.  The one above it to the right, with squiggly black lines on a white background, is Graphis scripta, the Script Lichen, so-called because it looks like handwriting.  The one with a greenish tinge below the Graphis and to the right of the Pyrenula is probably Pertusaria leioplaca.  The lichen community of smooth hazel stems is known as the Graphidion (after Graphis scripta, one of its main components)

In the second picture we see the next stage in the colonisation of the stem.  Small snaky liverworts are able to cling to the smooth surface, and grow over the crustose lichens.  This one is Frullania dilatata.  It has made its way across a patch of Thelotrema petractoides and a probable Arthonia species, and is about to invade a fine patch of Graphis scripta.  When the hazel stem has a good covering of liverworts like these, it presents a rougher surface on which more robust species can get a foothold.

The next stage is often dominated by Mousetail (Isothecium myosuroides), the green moss at the top of this picture.  The red liverwort to its right is Frullania teneriffae, a specialist of Atlantic woods.  These provide the kind of surface on which foliose (leafy) lichens can begin to grow, as Sticta sylvatica is doing here (above).

This belongs to a community of leafy lichens known as the Lobarion.  Most species in this community contain a cyanobacterium rather than a green alga like the majority of other lichens, and this accounts for their grey or brown appearance in contrast to the pale blue-green colour typical of lichens in most woods.  As well as providing food from photosynthesis, the cyanobacterial partner enables the lichen to obtain nitrogen from the air.

The Lobarion is the glory of Atlantic woodlands, and is named after the four Lobaria species which occur there.  The left-hand picture above shows two of these, the bluish-grey Lobaria scrobiculata at the top, and the green Lobaria pulmonaria (Tree Lungwort) below it.  L pulmonaria does have a green alga, hence its colour, but it also contains pockets of cyanobacteria.  In this picture both lichens have their “wet” colours; it must have been a particularly humid spot.

On the right is a famous Lobarion lichen, Pseudocyphellaria crocata (Yellow Specklebelly) which is unusual in having the interior fungal hyphae yellow rather than white.  This can be seen in eroded areas on the surface, from which small fragments of fungus and alga break off to reproduce.

As the hazel stems mature they can develop a luxurious growth of these leafy lichens, a sight familiar enough to us in Argyll but unknown in many parts of the country.  From left to right above we have the grey Degelia atlantica, the brown Peltigera collina, and a very dry-looking Lobaria pulmonaria.

The Graphidion lichens are almost completely obscured by this stage, but because hazel continuously puts up new stems there is always a supply of these for them to migrate to.  The succession of Lobarion lichens is equally assured, as by the time the old stems die and fall over, other stems will have become ready for colonisation.  A hazel in a state of nature has stems of all ages on the go at any one time.

When old hazel stems die they are often host to the fungus Stereum rugosum (Pink Curtain Crust), above left, which looks rather like a lichen but has no algal component.

The right-hand photo above shows how the Common Dog Lichen (Peltigera membranacea) got its name – the white rhizines on its lower surface are supposed to resemble dogs’ teeth, and for this reason it was once used to treat rabies.  It was on Hazel but is not a member of the Lobarion; it will grow in any damp shady place and is often found on disturbed ground such as beside forestry tracks.

Hazel also provides a vital food supply for many birds and animals.  Here a wood mouse has been tucking into its hoard of nuts, one of several such feeding-places we found in the wood.  You can tell that the holes are the work of wood mice by the tooth marks being on the outer edge only.

There was also a lot of birch in the wood, a tree with a completely different suite of lichens to hazel.  One of the commonest is Hypotrachyna laevigata, looking rather dry here and bearing fruits (apothecia) which are not all that common in this species.  It too is a specialist of Atlantic woods but prefers the acid bark of birch to the more alkaline hazel bark.  The broadly rounded sinuses between the lobes are characteristic of it.

We did find one mature birch with a thick growth of mosses that had been colonised by several Lobarion species, presumably able to ignore the acid nature of the bark as they were sufficiently removed from it by the moss cover.  They included this Leptogium burgessii (above left) with its red fruits (apothecia), and the tiny orange lichen Dimerella lutea (Tinned Apricots – above right) of which the fruits are the only visible part.  Must admit they look more like tinned apricots when they’re wet as the pale rim of the “tin” then shows better.

A glimpse of the woodland floor with Teddy Bear Moss (Rhytidiadelphus triquetrus) and frosted hazel leaves.

Carl Farmer, Joint Natural History Editor

All photos and text copyright © 2010 Carl Farmer