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"Cotton Candy" in the Forest

In the cold season of the year, formations that resemble cotton candy can often be spotted on dead trees in deciduous and mixed forests in different places of Latvia.

These peculiar white formations are to be found both on fallen trees, as well as on standing trunks. They are best to be spotted in very wet weather conditions; however, moisture alone is not enough. It is important that in the specific place the air temperature is a bit (quite slightly - less than a degree!) below zero and it should remain like that for at least two to three hours.

If there is no snow, this extraordinary "cotton candy" is easy to notice, but it is very difficult to find it in snowy weather. If you are lucky enough to notice it, take a closer look at it, touch it, shake it slightly. Why? Just to make sure: it's ice! It does not lie on a dead tree; instead, it winds away from the tree in the form of countless thin yarns that look like hair. The diameter of each yarn is about 0.01-0.02 mm, their length does not usually exceed 5 cm; however, ice bundles of up to 20 cm can also be found here and there.

The fine yarns can be twisted, curled, rolled up. They are capable of retaining their shape for several hours, in favourable weather conditions even for a few days. Sooner or later, the yarns, of course, melt or fuse into an even layer of ice.

The most observant will have noticed that the ice hairs tend to appear in the same place for several consecutive years. They are only to be found on deciduous tree trunks and only on the sections that are not covered by bark, on "naked" wood.

What forms the crystals of frozen water in finely shaped strands, rather than fuse them into a "normal" continuous layer? It turns out that already in 1918, German geophysicist Alfred Lothar Wegener argued that the formation of ice hairs is provoked by one of the winter-active wood fungi. And he was right; however, only a few years ago the researchers managed to find out which fungus it was.

Scientists from Switzerland and Germany representing three different areas of research in physical, chemical and biological studies conducted in winters from 2012 through 2014 found that these formations were caused by visually undistinguished fungus Exidiopsis effus, which belongs to the family of Auriculariaceae (Agaricomycetes class).

When a dead tree begins to freeze and water is squeezed out of the pores, the fungus releases special chemical compounds that prevent the water from spreading in an even ice layer. These substances cause each portion of the water to push back the crystals of already frozen water from the wood. Since the pores are distant from each other, a hair-like ice bunch is formed. If the temperature does not change, water displacement and ice repulsion continue - the "hairs" extend for as long as there is liquid water in the part of the wood inhabited by the fungus.

Scientists have discovered and explained the principle of the process of formation of the ice hairs, but, in their opinion, there is still a lot of uncertainty, therefore research on the fungus exposure mechanisms should be continued.