On my way to the old quarry I carefully pick my way through a clearfelling. I don’t know when the last stone was cut, but it must have been a while ago as a mature ash now stands right in the middle of it, and its heavy branches reach as if their twig fingers want to tickle the abandoned rockface. Even though this quarry is within rambling distance from home, I have never taken note of the bryophytes growing here. I am drawn by the sense of semi-permanence this quarry suggests and assume interesting bryophytes have made it their home. Now wondering why I thought I could reach the quarry in trainers rather than boots, I position my feet carefully between stumps and a mismatch of twigs and branches that hide holes. The bluish leaves of climbing corydalis have already softened this harsh clearfelling environment. Only a few years ago I stood here at a copse of wild garlic whose flowers had been a honeypot for hoverflies. This is a wood of opposites. Whereas I was after the bryophytes associated with semi-permanent rock faces, I was now treading through a recently felled plantation where the newly bared soil and removal of canopy shade had made it possible for the green mats of the disturbance moss Campylopus pyriformis to gain a foothold.

The contrast of this plantation felling with the natural pine woodlands around The Vat at Muir of Dinnet NNR could not be bigger. Winding my way through these I am sided by a continuous rather than interrupted mat of mosses that cushion the forest floor. I quickly pick out the usual suspects. The weft-forming Hylocomium splendens and Hylocomiadelphus triquetrus (formerly Rhytidiadelphus triquetrus) have a competitive edge and will quickly overgrow any smaller species. Away from the path, where the forest floor is much less disturbed, the foliage of these species forms and almost continuous carpet. Even though, one has to look carefully to find any sporophytes on these species. The Campylopus pyriformis that I had found on the clearfelling did not have any sporophytes either, but was entirely covered in branchlets, and each of these deciduous shoots would have the ability to start a new clump of moss somewhere close to the parent moss.

But even in the most stable forest wind will snap and uproot trees. Before the big storms two years ago eventually fell most trees, the wind had already uprooted some of the conifers at the plantations of Scolty near Banchory. I would often stop to have a look at these uprooted trees, intrigued by how the islets of bared soil and waterfilled pits quickly become colonised by species such as Atrichum undulatum, Dicranella heteromalla, Polytrichastrum formosum and Pogonatum aloides.

In the pinewoods at Muir of Dinnet NNR mossy logs show that some of the pine trees must, in the past, have experienced a similar fate as I find several logs with a lush covering of species like Hylocomiadelphus triquetrus, Dicranum scoparium, Hypnum cupressiforme and Pleurozium schreberi. In her book Gathering Moss, the American bryologist and writer Robin Wall Kimmerer describes how, between the competitive weft-forming species on such logs, she would find pockets of the much smaller moss Tetraphis pellucida, a species that is also widespread in Scotland. She found that this species tended to prefer the flanks of the logs where brown rot fungi had caused the wood to crumble, in turn creating new spaces for the species to colonise. Whereas many lichen species are able to reproduce through both spores and vegetative propagules like isidia and soredia, this phenomenon is much rarer in bryophytes. What she found, however, was that when space was available nearby, the moss Tetraphis pellucida would produce gemmae to fill these gaps. Gemmae are vegetative propagules that are relatively heavy and usually disperse no more than a few inches from the parent plant. When, on the other hand, all space was occupied this moss would produce sporophytes that could be carried on the wind to a new log some distance away.

Whereas Tetraphis pellucida was able to make a choice between sexual and asexual reproduction dependent on whether or not space was available locally for it to colonise, the reproductive effort of Hylocomium splendens and Hylocomiadelphus triquetrus on the forest floor at Muir of Dinnet appeared limited. The Dutch bryologist Heinjo During was among the first to recognise the link between the reproductive effort of bryophyte species and the durability of the niche these species would occupy. Distinguishing the potential life span of bryophytes, their overall reproductive effort and the quantity and size of the spores they produced, he discerned dominant life history strategies of bryophytes, and argued that those species with a short life span and high reproductive effort were likely to occupy disturbed habitats, while those species that live for many years and have a low reproductive effort are likely to occupy more stable niches. Robin Wall Kimmerer ‘s argument is about dispersal distance rather than niche stability, and I am not aware whether Heinjo During himself addresses asexual reproduction as part of his life strategies. The phletophera of deciduous shoots on the Campylopus pyriformis on the clearfelling can, however, be seen as a response to disturbance of the forest floor that would need to be colonised rapidly before competing species, such as the climbing corydalis would settle in. In contrast, the forest floor in the pinewoods of Muir of Dinnet NNR has not seen such disturbance and the weft-forming mosses found there are likely to be perennial stayers.   

In conversations, I often refer to myself as an ecologist rather than a lichenologist or bryologist as I feel that that reflects that I am driven by a quest to understand the ecology of those species groups rather than a pursuit of extensive species lists and finding that one rare species. And whether it be lichens or mosses and liverworts, each of these species groups allows me to develop an intimate understanding of the forest environment from a different perspective. In this way, the reproductive and life history strategies of bryophytes allow me to appreciate the forest as a layering of niches that are more – or less – durable. And I like it when, back home, I go through my species lists and realise that I not only have records to submit to a biological record centre, but also a repository of associated stories that add depth to my understanding of forest ecology.  

If you are interested in learning more about the ecology of mosses and liverwort you are welcome to join me on one of the following guided walks and training events:

• 4 February 2024, Muir of Dinnet NNR, a guided walk organised by Nature Scot (for more information and to sign up: Muir_Dinnet@nature.scot)
• 17 February 2024, Tilliefoure Wood, a guided walk organised by the Bennachie Wildlife Group (for more information and to sign up: environment@bailiesofbennachie.co.uk)
• 20 April 2024, Bennachie Visitor Centre, a one-day course organised by the Field Studies Council (for more information and to sign up: Bryophytes: An Introduction – Field Studies Council (field-studies-council.org))

Copyright text and images Petra Vergunst

There is an irony in planning to look at lichens in the riparian woodlands around some of the lowland lochs in Angus and then being caught off guard by the exceptional flooding in these areas that make these very woodlands inaccessible for the time being. The same rain that breathes life into these woods now is so excessive that those woods have become no more than a fringe of tree crowns in a sea of agitated water, in turn indicating normal water levels of lochs and rivers. The images of roads undermined by flood water around Marykirk and the streets of Brechin covered in a thick layer of mud after the water levels subsided, not only presses home the importance of riparian woodlands across the entire watershed, it also urged me to reflect on the role of lichens in these riverwoods.

Originally, I had intended to look at alder and willow as two of the most important constituent trees in riparian woodland, as I wondered whether the smooth and thin, acidic bark of alder would attract different lichen species than the corky, thick and nutrient-rich bark of willow. Surely, if lichens absorb water across their entire thallus and if that water runs off from branches and trunks, then that water will carry some of the properties of the bark of the tree species. I had assumed that this would mean alder and willow would host different lichen species, but an afternoon ramble through the alder woods at Loch of Park SSSI suggested the opposite. I found Peltigera species that can double or triple their dry weight when it rains, crustose species on twigs whose areolate crusts become continuous in humid conditions, and Bryoria and Usnea species whose thalli are water repellent to avoid becoming dislodged from the tree in rain under the sheer weight of water they would otherwise absorb. Both tree species, however, were host to a more or less similar range of species.

A few days after the worst flooding in Angus, I visited the riverwoods along the river Feugh near Finzean that are managed by Birse Community Trust. Though not in the worst affected area and further upstream, the wooded banks along this river were surprisingly accessible. Though there was birch, alder, willow, ash and hazel, I found only limited differences between the lichen floras on these tree species. Foliose species like Parmelia sulcata, Melanelixia glabratula, Platismatia glauca, Hypogymnia physodes and Evernia prunastri dominated, with the fruticose beard lichen Usnea subfloridana mixed in for good measure. The bare crowns of some of the trees and shrubs were entirely covered in lichen foliage. These lichens absorb water from rain and runoff, preventing this water from reaching the ground. Such lichen foliage thus slows down the runoff of rain and fertile topsoil downstream. Whereas many dehydrated lichens are able to become water saturated in a matter of seconds, the release of that water through evaporation tends to take place over a matter of hours or days. In doing so, this release of humidity to the air will keep the riparian woodland damp, thereby maintaining riverwood conditions. Researchers speak about this phenomenon in terms of water partitioning, with the lichens decreasing throughfall and stemflow by increasing interception loss.

Anyone who has been for a walk after heavy rain will have noticed the many tufts of foliose lichens like Evernia prunastri, and Ramalina farinacea, or even Ramalina fraxinea that, water saturated, were dislodged by the impact of rain. Once on the ground, however, these lichens are not mere biomass and water, but also an important source of nutrients. Cyanolichens, those that are formed through a symbiosis between a fungus and cyanobacterium species, are able to fix nitrogen from the air. These lichens tend to be more common in the temperate rainforests in the west of Scotland. In contrast, in the east of Scotland most lichens have a species of green alga as photobiont, and are only able to absorb the nutrients they need from water that runs across their thallus. Those lichens that were dislodged and are now at our feet will release those nutrients slowly, so that they become available for surrounding plants. Had rain water not been intercepted by lichens, but directly run off into the river, these nutrients would have been lost to the riverwood ecosystem.

There have only been few days between the warnings for heavy rain this October and my plans to look at lichens in the riparian woodlands surrounding Balgavies Loch, and Loch of Kinnordy and Loch of Lintrathen have been put on hold for a little longer. I know the lichens around these lochs will play their role in ameliorating the impact of the deluge we’ve been experiencing, and more widespread establishment of riverwoods further upstream in Angus Glens would play an even more significant role. With climate change, these downpours will only become more intense and frequent. Our response to it, through establishing riverwoods, will not only slow down the runoff of rainwater downstream and keep some of the nutrients in the riparian ecosystem, but it would also create new opportunities for lichens of both upland and lowland habitats. Perhaps, after seeing the images of roads undermined by rivers and mud-covered streets, that is a more hopeful picture to hold on to.

Copyright text and images Petra Vergunst

Several years ago I found myself passing time at a sheep fank at the foot of Shiehallion. It was early July, the morning skies were blue, and the car park at the foot of the munro had already filled up. Walkers would stop at the fank and ask, “I am looking for lichens, look at the colour of this little one”, and I would continue exploring the dykes until the next family would stop. A young meadow pipit seemed unconcerned about my slow progress along the dykes. This was my happy place – one so very different from the granite dykes I was used to exploring in Deeside. This sheep fank was a treasure trove with many lichen species I had not – or rarely – seen before.

The sides of the dykes were covered in crustose lichens like Acarospora cervina, Protoblastenia rupestris, Verrucaria nigrescens, Aspicilia contorta, Pertusaria corallina and Tremolicia atrata.  Among the mosses on top of the dykes Cladonia species like Cladonia furcata had made themselves at home. The rocks exposed on the slopes of Shiehallion are a mosaic of limestone, quartzite and schist and the lichen species I was finding suggest that each of these rock types was used to construct the fank. An unimaginable long time ago, these rocks were mollusc shells, sand and mud at the bottom on a seabed, and since then, they have become metamorphosed, folded and upturned to arise right here, at what we know as the slopes of Shiehallion.

In Scotland, limestone exposures are a bit of a specialty, and many of them occur in the Breadalbane Mountains that Shiehallion is part of. Limestone areas are not only important for the unique flora associated with it, many of the lichens species found on limestone are rare as well. Acaraspora cervina, Protoblastenia rupestris and Aspicilia contorta are clear indicators of the calcareous conditions created by the shells from which limestone is formed.

In fact, the limestone, quartzite and schist used to build the sheep fank each have their own chemical composition, texture and water holding capacity. Species like Lecanora polytropa, Lecanora intricata, Fuscidea cyathoides and Tremolecia atrata suggest the presence of acidic and metal-rich rock such as schist. One of the first questions someone studying lichens will ask is whether the rock the lichen attaches to is basic or acidic. Lacking roots and a vascular system to absorb and transport water and nutrients within their bodies, lichens absorb water across their entire thallus and any nutrients they need will have to be dissolved in that water. Though the crustose lichens on the side of the boulders are attached to the rock with their entire lower body, lichens are only able to absorb water and any nutrients dissolved in it from runoff that flows across the upper side of their body. Likewise, lichens that grow on the flattish top of boulders derive their nutrients from the thin film of water that will gather on flattish rock surfaces.

When geological processes expose rock at the surface of the earth, lichens are among the first species groups to colonise their surface, paving the way for mosses and eventually vascular plants. Even for lichens rock is a harsh environment to live on as it fully exposes them to scorching sun and drying winds with no protection whatsoever. And soon after the lichens arrive, the invertebrates that graze lichens will do too. For some lichen species this herbivory by slugs and snails may be so heavy that they regenerate endolithically, immersed in the rock.

Among the first colonists of recently exposed rock, lichens immediately set to work to break down the surface they are living on. On top of dykes you will often find thin sheaths of parched soil that flake off. Look carefully and you will find that these consist of organic matter mixed with tiny rock particles. Though there are other causes of rock weathering too, lichens play an important role in the breakdown of rock. While some lichens grow entirely immersed in rock, the hyphae of crustose lichens that grow on top of rock may still penetrate the surface several millimetres. The hyphae that thread between rock particles will swell and shrink in response to humidity and temperature, eventually contributing to the physical breakdown of the rock surface and soil formation.

If not interfered with, the soil layer on the sheep fank will build up to allow heath and grasses, and eventually trees to take root. The crustose lichens that are now covering the sides of the sheep fank will become smothered by vegetation. Where soil enters streams, water will flush the rock particles downstream, eventually disposing of them on the seabed where sediments, over time, will start a new phase in the cycle of rock formation. It is hard to believe that lichens, small as they are, play a significant role in processes that take place across geological time scales.

If you are interested in learning more about the lichens found near Shiehallion, I’ll be giving a guided walk at the adjacent Dun Coillich for the Highland Perthshire Communities Land Trust on Friday 11 August from 10 am to 1 pm. For more information, and to sign up, please click here.

Copyright text and images Petra Vergunst

For just fifteen minutes Correen Cottage is the centre from which I experience the world. I had been looking at this spot on the map, looked up its name on Canmore (Historic Environment Scotland’s online database), and imagined what it would be like. Now, with artists and family in tow, I have reached it through a metal gate and a dropping-littered field with sheep. The people who once inhabited it knew this land intimately, taking gravel and stone to construct tracks and houses from the quarry just yards from the garden, and peat to heat homes from Lumsden Moss on the other side of the village. The topographic map also tells me the cottage has taken its name from the Correen Hills beyond. What draws me to abandoned farmsteads and townships like Correen Cottage is that, what now is a blank square on the map, and perhaps even perceived by the farmer as an obstruction to the productivity of their land, once was the centre of someone’s world, and a place where living hinged on an intimate understanding of the surrounding landscape.

In my practice as a field ecologist I have long thought about local ecological knowledge. For the people who inhabited farmsteads and townships, the extensive personal observation of, and interaction with, local ecosystems, was essential to produce and gather food, fodder and fuel. With their abandonment, this knowledge and experience gradually went out of practice, and now even the memory of those practices among the local community and its diaspora is becoming lost.

When recording lichens, liverworts and mosses I often seek out abandoned farmsteads and townships like Correen Cottage. In the Grampians, unconsolidated granite walls may have lush coverings of the bluish foliose lichen Parmelia saxatilis and extensive carpets of the velvety moss Hypnum cupressiforme. In exposed situations there will also be plenty of mosses with hairpoints like the woolly Racomitrium lanuginosum. So here, on my visit to Correen Cottage I am welcomed by the bright yellow lichen Xanthoria parietina and cushions of the hairpoint mosses Grimmia pulvinata and Tortula muralis. In naming these lichens I read stories about acidic rock, traces of mortar, drying winds and scorching sun, perching birds and ammonia from livestock. 

The hand lens is an important tool for looking at lichens, liverworts and mosses. After gauging the position of the farmstead or township in the wider landscape and the built structures, trees and other features it comprises, I hold this lens close to my eye and bring my head forward until the lichen or moss is in sharp focus. A species like Grimmia pulvinata, looking but a hoary cushion with the naked eye, will suddenly reveal leaves that extend in silvery hairpoints and plenty of green or reddish brown spore-bearing capsules tucked between the leaves. What’s more, this close-up view allows me to appreciate how this species is able to grow on top and on the side of rocks rather than in the more sheltered and humid crevices between them as its hairpoints create an almost imperceptible layer of still air around the perfectly rounded cushions, in turn helping to retain moisture. To me, the hand lens expands, sharpens and clarifies. And it is the act of using a hand lens that kindles my emotional connection with the farmstead or township. What’s more, my understanding of the ecological requirements of lichens, liverworts and mosses, and the way they have adapted to live in challenging environments, renders an appreciation of the ecological conditions in that site. Yet, this is a glimpse and no more. My ecological practice at the farmstead or township is time-bound rather than ongoing, and I am not dependent on its environment for food, fodder and fuel. Looking at lichens, liverworts and mosses deepens my experience and appreciation of this blank square on the map, and the spaces framed by the four walls become filled with experiences of place. For just the duration of my visit, and emphasised by sharing my observations with artists and family, Correen Cottage was the centre from which I experienced the world.

This text was written as part of a research network run by the University of Aberdeen and University of the Highlands and Islands called ‘Creative Landscape Futures: Making Decisions with the Arts and Humanities’. It was funded by the Arts and Humanities Research Council.

Copyright text Petra Vergunst, copyright photos Jo Vergunst

To celebrate the Cairngorms Nature Festival from 12 to 21 May 2023, I was commissioned by the Cairngorms National Park Authority to write a self-guided walk inspired by the mosses of Morrone Birkwood on the outskirts of Braemar (owned and managed by Mar Estate). The walk follows the circular route (circa 2.75 miles or 4.5 km) through the reserve in clockwise direction and passes through birch and juniper woods, and moorland with bogs and flushes.

A species gallery of moss and liverwort species commonly found in moorland habitats, with links, with links to species descriptions, can be found here,

Copyright text and images Petra Vergunst

Earlier this spring I returned to the Highland Wildlife Park to deliver a number of lichen tours for staff. The lichen survey that would feed into the park’s biodiversity plan I had done the previous year had been a welcome way to continue some of my thinking about the interactions between lichens and animals.. At the time, I was still thinking of the lichens on the cliffs of the seabird colony at the RSPB reserve of Fowlsheugh that had shown significant influences of hypertrophication. Now, during the staff tours, we would be discussing another type of interaction between lichens and animals: lichen herbivory.

Though the Cladonia species they eat are, rather confusingly, often spoken about as reindeer moss, lichens form an important, and preferred, part of the winter diet of reindeer. The low cellulose and lignin contents make lichens particularly palatable to reindeer, and their richness in soluble carbohydrates makes them an important source of energy in winter. As large mammals with hooves, it is their rumen and bacterial flora that enables reindeer to break down this lichen carbohydrate. Caribou, the reindeer that live in America, eat, amongst other species, the terrestrial reindeer lichens Cladonia stellaris and Cladonia rangiferina as well as Stereocaulon species, which they find by kicking holes in the snow. In wooded areas caribou will mainly feed on tree lichens of the genera Alectoria and Bryoria, but they may also forage on Hypogymnia physodes, Tuckermannopsis ciliaris and even Lobaria pulmonaria.

The grazing pressure of semi-domesticated reindeer on lichen can be high, especially where their seasonal migrations are restricted. Though reindeer can eat grasses and mosses as well, they have been found to overgraze and deplete local lichen stocks. Had reindeer not been semi-domesticated, it would have been less likely that they would have overgrazed the lichens in their territory as their population would have been controlled by the food that is available to them. But the presence of reindeer may have a positive impact on lichens as well. Some of the mat-forming Cladonia species eaten by reindeer disperse through fragmentation. Cladonia uncialis subsp. biuncialis, for example, nicknamed the macaroni lichen, easily breaks into bits when put pressure on. So while reindeer are grazing, they will at the same time trample these mat-forming Cladonia species and contribute to their rejuvenation and dispersal.

But you don’t have to travel to high latitudes to find examples of lichen herbivory. When looking at crustose lichens on the trunks and branches of trees, many of us will have encountered crusts that seem to be covered in zigzag patterns or crusts in which apothecia have quite mysteriously been replaced by holes. These are the tell-tale signs of grazing by slugs and snails. Doing so under the cover of darkness, slugs and snails will scrape the thallus, leaving parallel scratch marks, with the zigzag patterns pointing out the side to side movements their mouths make. On limestone pavement the herbivory by slugs and snails can be so intense that lichens that usually form a crust on top of the rock develop an immersed thallus. Some lichens, however, have developed a chemical defence mechanisms in the form of lichen substances to make themselves less palatable. Ramalina siliquosa, a characteristic lichen of rocky shores, has developed at least four so-called chemotypes, each producing unique lichen substances that deter different species of mites from taking a nibble.

Sometimes, it is conversations with others and the exchange of experiences that help us take a closer look at our understanding of a topic. My conversations with staff of the Highland Wildlife Park have certainly helped me to place my understanding of lichen-animal interactions and lichen herbivory in a wider context. As primary producers lichens are at the bottom of the foodweb along with vascular plants and bryophytes. Though species interactions within the foodweb are usually balanced, human intervention may tip the balance and lead to overgrazing. Lichens, however, have adapted to withstand herbivory through chemical means. What’s more, some species have made a virtue out of it by using thallus fragmentation as a dispersal strategy. Even those spores that pass through the digestive system of slugs and snails are thought to remain viable.

Sources

Brodo, I. M., S. D. Sharnoff and S. Sharnoff, 2001. Lichens of North America. Yale University Press, New Haven and London.

Dobson, F. S., 2018. Lichens. An illustrated guide to the British and Irish species. The Richmond Publishing Co. Ltd.. Seventh revised edition.

Gilbert, O., 2000. Lichens. HarperCollinsPublishers, London.

Kijola, I. et al, 1995. Effects of lichen biomass on winter diet, body mass and reproduction of semi-domesticated reindeer Rangifer t. tarandus in Finland. Wildlife Biology 1(1): 33-38.

Copyright text and images Petra Vergunst

Caledonian pinewood: granny pines, a glimpse of a capercaillie, the drum of a woodpecker. Our imaginations of these woods seems infused with the sights and sounds of a mythical past that draws us to protect and enhance them for the future. The genetic continuity at the core of the notion of Caledonian pinewoods gives us a – perhaps false – sense of strength and stability. Yet, beneath the canopy of the remaining fragments there is true magic in a rich lichen flora that responds to, creates, and preserves, the forest conditions. 

Caledonian pinewood has a lot to offer to lichens. As the crowns of pine trees are relatively open, a lot of light reaches the branches, trunks and forest floor, in turn allowing lichens to settle as there is sufficient light to photosynthesise. Though many pinewoods are relatively dry, this is not a problem for the majority of pinewood lichens as the photobiont of so-called chlorolichens (containing green algae) can absorb moisture from humid air as well as liquid rain. What’s more, lichens are able to absorb the few nutrients they need from the runoff from bark and rock that flows over their thalli.

So if the conditions are right for lichens, how then do they gain a foothold? A quick look will soon reveal that there is plenty of surface for lichens to attach to: the trunks and branches of pines, dead wood, bedrock and boulders, the ground. Not all of these substrata, however, have the permanence that lichens prefer. Take bark, for example. The bark of both Scots pine and birch is flaky and peels off easily, and though lichens do attach, they may come off as bark detaches. The bark of mature Scots pine, however, is deeply grooved, in turn creating a much more interesting substratum for lichens. Higher up the trunk, for example, bark flakes may contain small patches of the crustose lichen Lecanora pulicaris. Inseparable from the bark, this species is a poor competitor as surrounding Hypogymnia physodes spreads its inflated lobes and wins the competition for light. Lower parts of trunk can be covered in the squamulose lichen Hypocenomyce scalaris, a species that attaches to the trunk like rooftiles, the top edge attached while the bottom edge sticks out and exposes soredia to the wind and passing animals.

Often the most conspicuous lichen cover on pine trees cushions and drapes from branches. Foliose species like Platismatia glauca and Parmelia sulcata often cover the top of the branch, while fruticose lichens like Bryoria fuscescens and Usnea dasopoga hang on below. These foliose species are anchored to the branch with multiple rhizines and seem much more securely attached than the fruticose lichens that have a single holdfast and easily break off if you tuck a little.

The forest floor provides mixed opportunities for lichens. Below Scots pine there often is a thick carpet of needles which is not a stable enough substratum for lichens to attach to. Where the canopy opens up a little, and on the side of paths, there may be patches of bare soil with good displays of Cladonia species. Beside the path there will also be boulders with even better Cladonia displays. These Cladonias may form thick mats and are anchored in the soil that has developed on the boulder over centuries. Through physical and chemical weathering, the crustose lichens on this rock have prepared the surface, while foliose species that followed trapped organic matter, including pine needles, and further accelerated the process of soil formation when they died back themselves. Only when enough soil has developed for Cladonia squamules to hold on to, the fruiting bodies to develop.

Once they have found the right conditions, lichens may have strategies to keep these conditions just so. When Cladonia species colonise a stump, dead wood decomposing fungi species are often not found immediately close by, and it has been suggested that this is because the Cladonia species actually contain lichen substances that deter fungi.  

To me, the magic of Caledonian pinewood lies in the fact that the remaining woods have provided continuity through centuries and developed into a mosaic of niches and substrata, each offering slightly different opportunities for lichens. The lichen diversity in pinewood reflects this. As key contributors to the early stages of soil formation, lichens will also contribute to the conditions that allow them to thrive. Pine seeds germinate and trees die, and in this cycle lichens have found a way of slowing the decomposition of dead wood to hold on for just a little bit longer. 

A picture gallery for lichens of upland pine and birchwood can be found here.

If you want to learn more about lichens in Caledonian pinewood, I’ll be leading a Field Studies Council course at Glenmore Lodge near Aviemore on 26 and 27 August 2023. More information on this course can be found here.

Copyright text and images Petra Vergunst

A ‘commanding view’ is the phrase the RCAHMS uses in their book In the Shadow of Bennachie to describe the hillforts of Donside. There is something captivating about visiting these hillforts. The expansive views, often across vast areas of lower lying farmland, and the appreciation that these hilltops were once not the destination for a leisurely Sunday afternoon stroll but viewpoints from which the surrounding land was scanned for possible intruders, certainly draws me in. Northeast Scotland is home to quite a few of these fortifications, and I’m gradually ticking them off.

The one closest to home, the Barmekin of Echt (west of Westhill, Aberdeenshire) has been a real eye-opener. On clear days this hillfort, rising no more than one hundred meters above the surrounding arable land and pastures, gives views as far as the North Sea. The path to the top winds through gorse, and then a combination of bracken, blaeberrry and wide-crowned Scots pines. The hillfort itself, several large, circular ramparts of exposed boulders, encloses an area of dry heath. The views from the top are commanding, but so are the lichen species I found on these fortifications. Indeed, there are the likes of Rhizocarpon geographicum, Lecanora polytropa, Acarospora fuscata and Umbilicaria polyphylla that also feature on dykes in the surrounding farmland, but there are also crusts like Ophioparma ventosa and Fuscidia cyathoides, and a galore of foliose and fruticose species including Sphaerophorus globosus, Cetraria aculeata and Cornicularia normoerica. These species I would not usually find on dykes and they seem to have more affinity with exposed acidic rock in the uplands, perhaps even scree slopes.

That this hillfort offers opportunities for lichen species that favour exposed acidic rock in upland situations was further emphasised when I returned recently to explore the bryophyte flora. Though some of the weft-forming bryophytes such as the ubiquitous Hylocomium splendens and Hypnum jutlandicum that grew through the heather and blaeberry sometimes encroached onto the rocks, on the top of the boulders there was only the occasional patch of Racomitrium lanuginosum, a sprawling moss with very long and wavy hair points that help create a layer of relatively still air directly around the moss to slow down dehydration by wind and sun. This may well be the adaptation most frequently seen in mosses that grow in exposed upland conditions. Every now and again there would also be a patch of moss in the slightly damper junctures between rocks, but liverworts only grew in the shelter of deep crevices between large boulders. On these fortifications I was seeing the exposed upland conditions played out as attempts by mosses and liverworts to stay as hydrated as possible in the face of drying winds and sun. Lichens seemed by far the group better adapted to these conditions.  

Exactly how special the lichen flora at the Barmekin of Echt is became clear when I visited the twinned hillforts at the Brown and White Caterthun near Edzell in Angus later last summer. On the Brown Caterthun the fortifications were covered in turf, the grass and heather smothering any opportunity for saxicolous lichens to gain a foothold. The fortifications on the White Caterthun were exposed and appeared slightly less extensive than those of the Barmekin of Echt, but perhaps the most significant differences were that the boulders used to construct these fortifications were smaller, perhaps also flatter, and that the fortifications themselves were hardly elevated above the level of the surrounding vegetation. I did find some of the lichens I had also seen at the Barmekin of Echt, such as Ophioparma ventosa and Pertusaria corallina, and in a small area with larger boulders on the side I also found species such as Umbilicaria cylindrica, Stereocaulon vesuvianum and Ochrolechia androgyna not seen at the Barmekin of Echt. Yet, it felt as if these exposed-upland species were less abundant. Location in the landscape and geology could explain some of these differences, but the size and shape of the boulders will have played a role as well. The larger and more rounded boulders at the Barmekin of Echt provided more niches for lichens by having exposed tops, more or less humid flanks, and crevices where boulders meet. This richness in micro-environments meant a more abundant and diverse lichen flora.

Ever since my visit last summer, I have wondered how it is possible that the ramparts at the Barmekin of Echt host a number of lichen species that are not found in the immediate surrounding landscape. The very essence of hillforts is that they are situated on hills from which the surrounding landscape can be scanned. This isolation makes the question how lichen species of exposed upland conditions may have reached the hillfort more pertinent. When I returned to the Barmekin of Echt recently, I was struck by the granite tor of Mither Tap on the skyline. Not only is Mither Tap one of the most famous hillforts in Aberdeenshire, as the summit of the Bennachie range Mither Tap is also home to similar upland species as the ones I found on the Barmekin of Echt. Spores of lichens are carried on air currents. It could well be that there has been an exchange of spore-dispersed lichens between the hillforts with exposed fortifications (and hilltops with similar exposed rock) in the northeast of Scotland.  

As I descended through the bracken and blaeberry and reached my familiar territory of Orthotrichum affine cushions on birch at the foot of the hill I was thinking about the relation between archaeology and the study of lichens and bryophytes. Had it not been for my interest in lichens, liverworts and mosses, I would not have appreciated the subtle, and not so subtle, differences in the way in which the hillforts like the Barmekin of Echt and the Brown and White Caterthun were constructed and are now presenting themselves. What further observations would arise if I continued to use lichens and bryophytes as a lens to look at the nature of hillforts more widely?

Copyright text and images Petra Vergunst

This is a place of intense beauty, the place where I expect to see a white-chested dipper scuttering along the edge of the burn when boulders have become submerged after days of rain. It is the place where I glimpsed that iridescent flash of blue and knew the trees heaving across the water are just the right habitat. It is the place to which I return in April to watch orange tips fly across the fen and to find the first peacocks bask on the dried reed sweet grass. This place, not far from my house, is where I take in and breathe out.

On a cold winter day the dampness of this wet woodland and fen gets to you as one carefully picks one’s way to the edge of the burn. I often stop beside the multitrunked alder with its cover of lichens like Evernia prunastri and Parmelia sulcata. In contrast to cyanolichens in which the fungus forms a symbiosis with a cyanobacterium, these chlorolichens thrive in locations that do perhaps not get as much rain, but are damp after all. Because of their photobiont being a green alga, they are able to absorb sufficient moisture from damp air to start photosynthesis.

Cyanolichens thrive better in areas where rain is a more persistent feature, not least the temperate rainforests on the west coast of Scotland. Cyanolichens also do well in areas that are frequently inundated such as boulders and rocks in streams. From the eastern bank where I stand it is hard to reach the rapids or boulders on the other bank, but a few hundred yards upstream others have found Collema flaccidum, a cyanolichen that requires a constantly damp substratum and thrives beside waterfalls. 

Instead, the few boulders and roots of alder that are within reach from the eastern bank of Leuchar Burn are covered in aquatic mosses such as Brachythecium rivulare. Like lichens, mosses are poikilohydric, which means that they can stop and start their metabolism according to the amount of moisture they are able to absorb. When water levels recede after a dry spell, these mosses shrivel, but as soon as the levels rise again, the mosses will absorb the water and start photosynthesis again. And lichens and mosses respond in a similar manner to rain.

The trees along the water edge are like a thin necklace strung between burn and fen. In winter the reed sweetgrass in the fen has succumbed to the ground, forming a thick layer of rotting plant material. Lichens are unable to live beneath. This mat is simply too thick and blocks out the light they need to photosynthesise. In shaded and damp habitats mosses often seem to have a competitive edge over lichens. In the area of fen where peacocks tend to warm in the sun, there are a few openings in the vegetation where, rather opportunistically, the moss Thuidium tamariscinum has plugged the gap. Its upward-reaching habit allows it to come level with the dead vegetation, and so it creates a level playing field when it comes to competition for light. 

A sprawling willow with thick boughs marks the edge of the fen. On one of the younger branches there is a vivid patch of the lichen Platismatia glauca alongside some crisped cushions of the moss Ulota bruchii. The older branches and leaning trunk are covered in a thick layer of weft-forming mosses such as Hypnum cupressiforme. This trunk is crowned with a large patch of the lichen Peltigera hymenina. I have another look and realise how, despite having seen lichens and mosses swell and shrivel when they get wet and dry out again, I often lazily assume the lichens and mosses growing on a tree to just be there, and to still be there when I return. But on this trunk, Peltigera hymenina is fighting it out with Hypnum cupressiforme. The large thalli of the Peltigera species lie pressed against the trunk, blocking out any sunlight for the moss. Yet, wherever there is a gap between thalli, stems of the Hypnum species shoot up and across the lichen thalli. This is competition unfolding. I take in and breathe out. When I return a year from now, the score between the lichen and moss may well have changed.

Culter Burn is designated a Local Nature Conservation Site for its long-established woodland with a rich ground flora, and its reedbeds, marsh and willow scrub.

Sources

Baron, G., 1999. Understanding lichens. Richmond Publishing, Slough, England.

Gilbert, O., 2000. Lichens. HarperCollinsPublishers, London.

Porley, R. and N. Hodgetts, 2005. Mosses & Liverworts. HarperCollinsPublishers, London.

Copyright text and images Petra Vergunst

What is the substratum, we often ask ourselves when discussing the identification of a lichen, is it basic or acid? Frank Dobson’s Key to Churchyard Lichens is arranged along the lines of substratum. Dobson’s Lichens and Smith et al.’s The Lichens of Great Britain and Ireland, however, also address the association of certain species with additional environmental conditions, such as lowland-upland gradients and relative pollution levels. I have often wondered about the relative importance of substratum and environmental conditions on the distribution of lichens, and how these conditions relate to each other. To learn more, I set out surveying twelve churchyards from the mouth to the source of the river Don in North-East Scotland, with the locations of the churchyards representing not only the gradient between lowland and upland, but also different levels of both (historic) sulphur dioxide pollution in a city and town, and nitrogen dioxide pollution in farmland areas.

Making sure I visited at least one church in each hectad, I thus surveyed the churchyards of St. Machars Cathedral in Aberdeen, Dyce Old Kirk, the cemetery and historic churchyards in Hatton of Fintray, and the churchyards in Kintore, Monymusk, Keig, Bridge of Alford, Kildrummy, Towie and Strathdon, followed by the cemetery in Corgarff. Though I did look at lichens on trees where present, here I focus on the saxicolous lichens as found on the gravestones, the church building and the boundary wall.

Each churchyard was visited for around an hour, during which I usually started with a detailed photographic record of the first three to five gravestones of each type (granite and sandstone, and tombstones), followed by a slow walk through the remainder of the churchyard to record any additional stones on which there appeared to be additional lichen species. Back at home, I would then identify the lichens (and make a list of unidentified species) on basis of good quality macrophotography, a combination of the above-mentioned guides, and photos on reliable online websites. A good knowledge of the lichen species, and lichen associations, found in NE Scotland helped with the confirmation of identifications.

In total, I found 75 lichen species, but this ranged from 12 to 34 saxicolous species per churchyard, with lowest numbers in churchyards near the mouth and highest numbers closer to the source of the river Don (see Table 1). When reading chapter on churchyard lichens in Oliver Gilbert’s Lichens, I was struck by the apparent diversity of substrata of gravestones and church buildings elsewhere in Britain. The rock type of gravestones did become more diverse as I moved upstream, but some churchyards consisted almost exclusively of granite. Though more abundant in historic churchyards, sandstone memorials were almost absent from modern graveyards. Only handful of instances marble or basalt gravestones were found. In addition, some of the churches were pebble-dashed in part or in whole.

Table 1: Churchyard lichens along the Don (the churchyards are arranged from the mouth of the river Don upstream: St. Marchar Cathedral (Aberdeen), Dyce Old Kirk, Hatton of Fintray Cemetery, Fintray Old Parish Church, Kintore, Monymusk, Keig, Bridge of Alford, Kildrummy, Towie, Strathdon, Corgarff).

This relative lack of diversity of saxicolous substrata in churchyards may well have been responsible for the relatively low numbers of species found in this survey. What’s more, the churchyards of St Machar and Kintore were clearly influenced by (historic) sulphur dioxide pollution and many of the lichen species here were no more than thin stains that could not be identified through photography as they lacked well-developed crusts and reproductive features. The churchyard of Towie stood out as it was almost entirely sandstone.

Along the Don there were a few clear shifts in the landscape. Somewhere between Kintore and Monymusk one moves from a more open lowland landscape with intensive arable and livestock farming to a mixed landscape with low hills and a combination of conifer plantations, estates and more or less intensive farming. Further upstream, between Towie and Strathdon, the hills become more exposed, still with conifer plantations, but farming lower down the slopes becoming more extensive. Interestingly, this seems to be reflected in the lichen species found. Nine out of the thirteen species found in St Machar churchyard are common species that were found along the full course of the river upstream. The first new introduction of species, those commonly found on bark of conifer trees as well, is in the historic churchyard of Fintray, which is surrounded by woodland. Then, at Bridge of Alford, another assemblage is introduced, with species that are also associated with conifer trees in more upland conditions. From Strathdon upstream, lichen species associated with upland landscapes are introduced. In a way, this stepwise introduction of species when one moves upstream is captured in the three Umbilicaria species found in this study. Umbilicaria polyphylla, first found in Bridge of Alford, is a species that can be encountered on dykes in the mixed farmland and conifer landscape in the middle reaches of the river Don. For Umbilicaria cylindrica, first encountered in Strathdon, one tends to have to travel well to the middle reaches of the river, and be in more upland settings. Umbilicaria proboscidea, only found near the source of the river in Corgarff, one would usually only encounter in the hills.

So what did I learn from this exploratory study regarding the relative importance of substratum and environmental conditions in determining lichen assemblages in churchyards? At the moment, my thinking goes along the lines of the substratum being an enabler, determining the range of species that one can possibly find.

Environmental factors such as the lowland-upland gradient, and associated landscapes and pollution levels, however, seem to put limitations on this range, shrinking that vast number of possible species on a certain substratum to a much smaller number. This exploratory and descriptive study is not the place to quantify the relative importance of substratum and environmental conditions for lichen assemblages found in churchyards, but it has shown the complex interplay between the factors that is difficult to reduce to substratum alone.

This article was first published in the winter 2022 edition of The British Lichen Society Bulletin.

This blog builds on the earlier blog post Churchyard Lichens along the Don.