In the middle of December, on a cold and frosty morning, I decided to make a return visit to Inverfarigaig, to explore more of the temperate rainforest in the gorge there. I’d spent a very satisfying day at the site in early November, which featured in a recent blog I wrote, and my appetite had been whetted then to discover more of this special area, on the southeast side of Loch Ness. On that day I’d spent almost all my time in a very small section of the gorge, and I suspected that there would be a lot more of interest, if I looked at other parts of the area.
Another reason for going was that I’d photographed some bracket fungi on a fallen log on that earlier visit, thinking it would be straightforward and easy to identify them from the photos when I got back home, but that had turned out not to be the case. I hadn’t collected any samples of those fungi in November, so I planned to do so now, so that I could send them to Liz Holden, the mycologist who helps me with fungal identifications. Upon reaching Inverfarigaig, I headed straight for the log with the bracket fungi, near where a tributary burn flows into the Farigaig River itself, and collected one of the many brackets on it as a specimen.
While I was doing this I noticed some unusual white patches on the dead stems of a couple of hazels (Corylus avellana) a few feet away, so I went to take a closer look at them. As I approached I could see that the patches were composed of very fine and delicate white strands of ice packed closely together, and all lined up parallel with each other. I assumed that these formations were what are known as frost flowers, which I’d heard of before, and had seen photographs of on various occasions, but I hadn’t encountered them personally until now. They were extraordinarily beautiful, and I studied them closely with appreciation and wonder, whilst trying not to breathe out on them, which could have led to them melting from the heat of my breath. It was an almost perfectly wind-still morning, but an occasional slight breeze caused some of the filaments to vibrate very slightly in the gentle air currents, almost like the strings of a harp.
It was only a few days later, after some of the photos I took were posted on Trees for Life’s Facebook page, that I discovered, as a result of someone’s response there, that this phenomenon is called hair ice.
Apparently, hair ice only occurs on dead wood (whereas frost flowers can appear on living plants), and does so on nights when the air is humid (i.e. with a lot of moisture content) but just above freezing, while the ground temperature is just below zero degrees. Although this phenomenon has been known of for a long time, and a theory was first postulated for its cause over a century ago, it was only in 2015 that it was confirmed that it is the presence of a fungus, Exidiopsis effusa, that is the key factor in the development of these beautiful ice shapes.
The fungus facilitates the formation of these very thin filaments of ice, which have a diameter of about 0.02 mm, on exposed dead wood (never on tree bark) and enables their continuous growth or extrusion into these parallel curled shapes. A time lapse video showing the growth of some hair ice can be seen here on the BBC website.
Individual ice hairs can be up to 20 cm. long, but are ephemeral, melting as soon as the temperature rises, or the sun shines on them. However, in ideal conditions they can persist for hours or even some days, with the fungus acting like anti-freeze, preventing the individual hairs from recrystallising and merging together to form larger ice structures. This has been confirmed by experiments in which the fungus was removed with a fungicide, and although ice still formed on the wood, it was of a more normal crust-like shape, without all the individual hairs in parallel with each other.
I found a number of these dead hazel stems in the vicinity that also had hair ice on them, including some with multiple patches. It was also very obvious that the phenomenon was only occurring on dead hazels, as there was no hair ice on living ones.
After spending quite a while with the hair ice, I turned my attention to another manifestation of the cold weather – delicate crystals of frost that were adorning various lichens and mosses on the trees. As a temperate rainforest, this woodland in the gorge at Inverfarigaig is characterised by an abundant proliferation of moss and lichen species that cover many of the trees, the rocks and in some places the ground itself, giving the site the characteristic lush, green, exotic appearance of this ecosystem.
Some of the hazels were hosting good colonies of tree lungwort (Lobaria pulmonaria) – one of the largest lichens in the UK – and the presence of which is an indicator of temperate rainforest, both here in Britain, and more commonly, in other parts of its range such as the Pacific Northwest of North America. Tree lungwort is easy to identify, with its large, irregularly-shaped lobes, which have a rippled green surface to them. On this day, they were all fringed with a delicate tracery of frost crystals, making them stand out from the moss behind.
This gorge area at Inverfarigaig provides ideal conditions for these temperate rainforest lichens to flourish, and the extensive patches of tree lungwort there are some of the largest I’ve come across in Scotland.
On some of the hazels there were clusters of another group of large foliose, or leaf-like, lichens – the dog lichens (Peltigera spp.). There are a number of different species of dog lichens occurring in Scotland’s temperate rainforests, and as a group they are easy to recognise, although it’s harder for a non-expert like me to identify individual species amongst them. In this case I had to rely on the assistance of John Douglass, a lichenologist who helps me with identifications, to name the particular species I photographed.
All lichens are compound organisms, consisting of a fungus and an alga growing so closely together in a symbiotic, mutually beneficial relationship that they are only given one scientific name. However, the dog lichens, like tree lungwort, have a third partner in their symbiotic partnership – a cyanobacterium (Nostoc sp.). Cyanobacteria have the ability to absorb or ‘fix’ nitrogen from the atmosphere, incorporating it into their physical structure, and when the lichens they are part of die and fall to the forest floor, this nitrogen becomes available for other organisms to utilise. This is therefore one of the ways in which the forest improves its own fertility, through the transfer of nitrogen from the air to plants and then the soil.
The brown lobes on the edges of the dog lichen’s thallus are called apothecia, and these are the structures that release the spores of the fungal partner in the lichen.
With the frost decorating the lichen apothecia like tiny chandeliers, there was a whole miniature world of wonders to explore on the branches of these fallen hazels, and I spent quite a while marvelling at these delicate and ephemeral works of natural art.
The mosses too were festooned with frost, and the shapes of these tiny ice structures seemed to echo, and extend, those of the leaves of the mosses themselves.
Some patches of moss were distinguished by the spore capsules rising vertically up out of their foliage, creating a diminutive landscape of bryophyte periscopes, seeming to peer at their surroundings. In reality, of course, the capsules contain the moss’ spores, and their additional height facilitates the distribution of the tiny spores by the wind, enabling the moss to establish new colonies at suitable sites some distance from their parent.
My attention kept being drawn back to the dog lichens though, and I spent quite a long time taking photographs of them. I’m fascinated by the patterns and shapes of their apothecia, and how they contrast so dramatically with the thallus in their colour, form and texture.
Eventually I did move on however, and went over to the edge of the watercourse, where the small tributary burn merges with the Farigaig River itself. The moss-covered trees there create a strong and vivid visual impression of the green lushness of the temperate rainforest ecosystem.
It was now the middle of the afternoon and the daylight was beginning to fade. There were some other patches of hair ice nearby, so I finished up for the day by taking a few more photographs of them.
Having never seen hair ice before, I’d spent much of the day appreciating and photographing this remarkable phenomenon of Nature. I’d been aiming to make the most of the unique opportunity offered by the conditions at Inverfarigaig on this day, recognising that it might be years before I encountered hair ice again.
With thanks to John Douglass and Gordon Rothero for their assistance in identifying the lichens and mosses respectively, that are featured in this blog.