Friday, 15 January 2016

10 years for an id

Back in December 2005, I encountered a hair-like ice formation on grounded twigs in Steeple wood. I thought it might be related to some kind of fungus, since the twigs were clearly rotted to some extent, but I couldn't get an id. In July 2015, Swiss scientists discovered that the 'Hair Ice' is caused by the crusting fungus Exidiopsis effusa, but only when a precise set of conditions is met.

It seems that water is drawn into the twig, saturating it, and the crust fungus exudes the water through pores. When the temperature, humidity and air are exactly right, the extruded water freezes and forms the hair-like structures we see in these photographs.

'Hair Ice' caused by Exidiopsis effusa 

'Hair Ice' caused by Exidiopsis effusa 

There is one previous record of the fungus from Ireland, made in 1993, but I suppose that must have been the original crust, rather than the 'Hair Ice'. So I have to settle for a second Irish record, with a Donegal first.

10 years for an id isn't too bad I suppose.

Coincidentally, we are experiencing the first cold snap of the winter, with lying snow and sub-zero temperatures. This was the view from my front window this morning as the sun rose behind falling snow:


The Weaver of Grass said...

Stuart - does this (and the photograph) merit another letter to The Times - or at least to Derwent May? That photograph at the end of your post is beautiful.

Gill said...

Fascinating - have the researchers actually seen the hair-ice growing? I wonder how long it takes?

stuart dunlop said...

There are time-lapse videos of the process on Youtube and the paper announcing the discovery shows the Ice Hair in lab conditions. The conditions appear to be damp deciduous wood with the fungus present on the wood, humid air, sub-zero temperature for formation and sub-zero after the hair production. That certainly matches what I have seen. There are plenty of sightings of Ice Hair on record, but only now can we submit formal records based on isolation of the fungus that's responsible. The precise mechanism that leads to the formation of the hair is still not clear, but it appears to be the result of freezing water expanding and being forced out of channels in the partially-decomposed wood whilst under the influence of an agent that inhibits immediate crystalisation.

Peter Archdale said...

Stuart, as you say, this is very common - I would see it maybe 20 times a year in different locations across Tyrone and Fermanagh. Few things happen by chance where nature is concerned, so I wonder what evolutionary pressure produced this response. Maybe the wood is too wet for the fungus to be able to digest it optimally?

stuart dunlop said...

Peter, it depends on how easy it is for the fungus to perform its trick. If it doesn't have to do any work to create the circumstances, perhaps the 'hairs' are just a by-product of physics. For example, snowflakes have a complicated structure that didn't involve evolution. They just 'are'. If, however, there is any deliberate action taken by the fungus to bring about the ejection of the water as you suggest, then there must indeed be that purpose. I tend to look on 'difficulty' as the defining factor. If something is difficult to do, then it most certainly must have a purpose. The example I use for this is Holly. We know that Holly makes spines on its leaves for protection, but when the tree grows tall it stops making the spines on the top branches. So we have to assume that it's some relief to the tree to stop making them, otherwise it wouldn't bother changing pattern. My deduction, then is that spines are expensive or difficult to make, so are abandoned when the tree is tall enough. Why carry two patterns if one would be fine? As an aside, can you work out how the tree knows when to stop making the spines? For example, some Holly trees that have been blown over by the wind and have a low 'top' still make the spines, so it isn't age....