Sustainability News

Arctic-Alpine Lichens: Hiding in Plain Sight

Nathan Chrismas is an Aspirant AC Member and lichenologist. He studies the diversity and function of lichens in polar and alpine environments. His latest project, CryptFunc, involves understanding the functional ecology of Arctic-alpine lichens in the Cairngorms. Here he explains more about these remarkable organisms and how their distribution is being impacted by environmental pressures.

^{The elegant sunburst lichen (Rusavskia elegans) on the south-east ridge of the Weissmies (AC Aspirants Meet, 2023) - Nathan Chrismas}

Mountains can be inhospitable places. Biting winds, long cold nights, exposure to the sun, and lack of food are all familiar experiences to alpine climbers. Mountaineers tend to be hardy folk though and are happier than most to tough it out when conditions turn grim. But even the most resilient among us don’t come close to another group of mountain enthusiasts: the lichens.

Lichens are a paradox. They are incredibly abundant, having found ways of colonising almost every terrestrial habitat on the planet. By some estimates they are dominant organisms on as much as 8% of the Earth's surface. Yet to our eyes they are often invisible, obscured by their ubiquity. It is only when they are at their most flashy that lichens draw our attention - a bright orange splash on the tip of a boulder, a fluorescent yellow tangle on the trunk of a tree - but look closer and you will begin to see lichens everywhere you look. This is no more true than for climbers and explorers. The most exposed sea cliffs, the highest mountains, and wide expanses of Arctic tundra; all are home to a rich diversity of lichens growing on rocks, soil, moss, and plants.

Their biology is fundamental to their versatility. It’s almost impossible to find anything living in complete isolation, and lichens quite literally embody this principle. They are a fungus and algae living in close coordination with each other; the algae generating enough sugar through photosynthesis to nourish both themselves and the fungus, while the fungus provides a structure within which those algae can grow. It’s this symbiotic relationship that has allowed lichens to occupy such an incredibly diverse range of habitats. By ‘farming’ algae, the lichen fungus can survive in places nothing else can, including the polar regions and the high mountains. Interestingly, the word ‘symbiosis’ was first invented by Albert Bernhard Frank in 1877 to describe the relationship seen in lichens.

In the UK, mountainous lichen habitats are no more apparent than in the Cairngorms. These granite hills are a unique environment on our islands. Scotland’s latitude means that species associated with the high mountains in central Europe can survive here at much lower elevations. The relatively dry Cairngorm Plateau has characteristics reminiscent of Arctic tundra, the sort of landscape more readily associated with Finland or Svalbard. Just as reindeer roam the broad expanses of tundra in Finland, so the Cairngorm reindeer herd have made the plateau their home. When winter comes, both Scottish and Scandinavian populations turn to the only reliable source of food: reindeer lichens. These bushy species, like Cladonia arbuscular, cover huge areas of exposed and wind-clipped terrain, dominating in landscapes where flowering plants are at their limit.

^{The author examining lichen heath on Meall a’ Bhuachaille}

Both the mountains and the polar regions are changing, and the lichens along with them. The highlands of Scotland already support relict populations of lichen species that were once widely distributed at the end of the last ice age, creeping further northwards and to higher elevation at a literally glacial pace as the ice retreated. Today, as our climate warms more rapidly than ever before, these shifts in the distribution of lichen populations are happening right before our eyes. The white worm lichen (Thamnolia vermicularis) is a true arctic-alpine specialist that can be found fairly frequently in the Cairngorms. However, last year it was declared extinct in North Wales, presumed lost to warming, grazing, and trampling. Many more lichen species are likely to suffer a similar fate.

Of course, lichens will always be there in the hills. Whatever the environmental conditions, there will almost always be lichens adapted to them. But the species we see are not as fixed in stone as they might appear and the arctic-alpine specialists are important ones to watch as our global climate changes.

^{White worm lichen (Thamnolia vermicularis) growing amongst a bushy reindeer lichen (Cladonia arbuscular) on the Cairngorm plateau - Nathan Chrismas}

Lichens are amongst the most under-studied groups of organisms on the planet and there are still many open questions about the fundamental principles that underlie their biology and ecology. They play an as yet poorly understood role in global nutrient cycles, introducing and recycling carbon and nitrogen in otherwise nutrient depleted environments. Our new research project based in the Cairngorms hopes to shed some light on these processes and explore what lichens at home can tell us about the fate of a future Arctic.

Other projects are focusing on the mechanisms behind the interactions between fungi and algae, probing the very nature of mutualistic interactions; it’s an exciting time to be involved in lichen research. All of this, while the questions of how many lichens are even out there remains unanswered. New species are still being described here in the UK and, with no baseline estimates of lichen biodiversity in many of the planet’s most remote regions, the race is now on to document as much as we can about these remarkable organisms as they respond to their rapidly changing habitats.

If this has piqued your interest, below are a few species to keep an eye out for the next time you’re in the Cairngorms, the Alps or anywhere cold or high. You can also find more information on the lichens of the Cairngorms in The Montane Heathland Lichen Guide by Andrea Britton.

^{Alpine bloodspot lichen (Ophioparma ventosa): This eye-catching Arctic-alpine grows on rocks and gets its name from its bright crimson fruiting bodies.
It has a fairly broad distribution and can be found as low down as Dartmoor.}

^{Grey Witches hair (Alectoria nigricans): This dark lichen can be hard to spot and looks like a tuft of hair.
It grows near the ground in very wind-exposed environments like ridges.}

^{Iceland lichen (Cetraria islandica): This is a ‘shadow lichen’ of alpine heath; hard to spot, but when you know what to look for you’ll start seeing it everywhere!}

^{This lichen can be brewed into a tea and you can buy it in corner shops in Iceland.}

^{Map lichen (Rhizocarpon geographicum) photographed on Skye’s Inaccessible Pinnacle (AC Highlands and Islands Meet, 2023)}

^{Crinkled snow lichen (Flavocetraria nivalis): This pale yellow leafy lichen is a common sight on alpine heath, but in the UK is only found in the Cairngorms.}

^{Its colour works as a sunscreen to protect it from exposure to UV radiation.}

You can follow Nathan Chrismas on Twitter, Threads, Facebook and Instagram.

You can also catch him in the new BMC series The Landscape Project which explores the natural history (including lichenology) of UK climbing venues.

Arctic-Alpine Plants: Engineers and Warning Bells

In the UK, arctic-alpine plants are a key component of upland habitats, laying the groundwork for insects, other plants and larger predators to survive in mountain environments. But new research suggests that these species are under threat; withdrawing uphill and perhaps on the verge of vanishing from our slopes entirely. Sarah Watts, a PhD researcher in plant ecology and conservation at the University of Stirling, explains why these plants are so important and why they’re currently in retreat.

^{From Left to Right: Purple saxifrage, snow pearlwort and drooping saxifrage - Sarah Watts}

When most people consider the arctic, or high-altitude mountain landscapes, they think of endless snow, ice and bare rock. But pastel-coloured flowers, sometimes just a few millimetres wide, bloom in these dramatic places too. These miniature flowers not only weather some of the toughest habitats on Earth, but can also help to engineer the landscape for other species.

Don’t be fooled by their delicate petals. Some species of rock jasmine and sandwort grow at well over 6,000 metres on Mount Everest, while purple saxifrage flourishes on the northernmost point of land in the world – Kaffeklubben Island, north of Greenland.

Plants in freezing cold environments are typically small and often form as ground-hugging rosettes, or dense tufts with short stems, known as “cushions”. Antarctic pearlwort sits no more than 5cm high and displays a tight bunch of minute yellow blooms. The summits of the Scottish Highlands, where temperatures can drop to -27℃ in winter, are home to tiny flowers also found in the Arctic, such as moss campion, dwarf willow, trailing azalea and starry saxifrage.

^{Trailing azalea close up - Sarah Watts}

^{Moss campion, a mountain wildflower - Sarah Watts}

Although plants such as these may appear fragile, their minute size helps them cope with freezing weather and fierce winds. Low stature and tightly packed leaves act as an aerodynamic trap and storage system for water and solar radiation. Microspaces within the dense, dome-like foliage are efficient structures for retaining moisture and heat. An arctic-alpine cushion’s internal temperature can be 15°C warmer than its surroundings.

Cushion plants and mosses can be integral to their local environment. They are known as “keystone species” and “ecosystem engineers” because they stabilise their harsh microclimate, and are often the first to colonise bare ground. As the cushions grow, they improve the moisture and nutrient content of thin soils by accumulating organic material both directly within the plant itself, and through their root systems. By buffering temperature extremes, cushions reduce the frost risk in their immediate surroundings. These processes create a habitat more suitable for less stress-tolerant plant species including arctic-alpines in the daisy and pea families.

Cushion formers are therefore vital “nurse” plants in mountain and polar regions. They also shelter small arthropods including beetles and tiny wingless insects called springtails. These animals may in turn pollinate the plants they take refuge in, and provide food for others higher up the food chain.

^{A rove beetle on snow pearlwort - Sarah Watts}

However, these tiny arctic-alpine plants are now sounding a warning bell for the loss of biodiversity due to climate change. The plants have an important relationship with snow, which offers them protection from disturbance and erosion. But rising temperatures are causing earlier snow melt, allowing the spread of other species previously restricted to lower altitudes and latitudes. Consequently, taller generalist plants, such as common grasses and sedges are crowding out the smaller arctic-alpines.

High mountain areas are warming at twice the global average and are geographically isolated from other places with similar climates, leaving the specialist flowers nowhere to relocate to.

Arctic-alpine plant numbers are plummeting in Britain and climate change is impacting numbers across the world, threatening the future of species that depend on them. Snow pearlwort, a cushion plant usually no bigger than a penny, is the first flowering plant in Britain to have its International Union for the Conservation of Nature status moved from vulnerable to endangered due to climate change. Our research analysing long-term monitoring data from the Ben Lawers National Nature Reserve in the Scottish Highlands has revealed that the British population of snow pearlwort declined by 66% between 1996 and 2019. These data, collected for over 40 years by National Trust for Scotland staff and volunteers, also show that two other arctic-alpine plants have lost over half of their population since the 1990s. As temperatures have risen, snow pearlwort, mountain sandwort and drooping saxifrage have all withdrawn uphill. What’s more, these species face mountaintop extinction here in the UK because there is no higher ground left for them to retreat to.

^{Snow pearlwort growing on Scottish munro Ben Lawers - Sarah Watts}

If we lose these plants from their British mountaintop outposts – at the edge of where they occur globally – this will signal that their strongholds in the Arctic and the Alps are also in danger.

Polar and mountain regions are havens for biodiversity, nurturing species found nowhere else in the world. We risk losing the cultural and inspirational value that rare species give us, with implications for the preservation of our natural heritage.

Plants are the building blocks of habitats and food webs on which other lifeforms across the planet depend, but they are frequently overlooked in conservation news stories. There’s a name for this phenomenon – “plant blindness”. Scientists, nature writers and the media usually turn to trees or species with large colourful flowers to open people’s eyes to the importance of plant life. But we must celebrate and protect our tiniest of plants too. If we don’t, the spectrum of diversity across the Earth’s extremes will be lost for generations to come.

- Sarah Watts (PhD researcher at the University of Stirling)

A version of this article originally appeared on The Conversation. Changes have been made with the permission of the author.

You can read Sarah’s research via Science Direct and follow her on Twitter.