Hair Ice is Doped for Beauty

Late one frosty morning, I paused my walk to admire ice crystals that had grown from a small branch lying on the ground. Delicate and lacy to the extreme, the ice had a silky and well-kempt appearance. The formation was gorgeous.

silky ice, parted neatly in curls, growing out of dead wood

This was my first glimpse of hair ice, a phenomenon that originates in a surprising way.

If you live in a temperate climate that experiences hard frosts, you might be familiar needle ice. Even though it forms on frosty nights, this type of ice isn’t frost because it doesn’t condense out of the atmosphere. According Dr. James Carter of Illinois State University, it forms instead from in water in soil through ice segregation, a process when “above freezing and below freezing temperatures are juxtaposed. At the Earth’s surface this is most common in fall at night as the air cools to below freezing while the land surface stays relatively warm.” As ice forms on the soil surface, liquid water is pulled up from below through capillary action and freezes to the existing ice. This forces the ice to grow away from the freezing surface. The process stops when the temperature becomes cold enough to freeze everything up, the temperature rises above the freezing point of water and everything melts, or the soil surface becomes too dry.

Hair ice however, forms under even more specific, and perhaps unusual, circumstances. Like needle ice in soil, hair ice needs air temperatures just below freezing and a water saturated substrate. Unlike needle ice though, hair ice forms only on wood, specifically the dead and bark-free wood of broadleaf trees. Why only on dead wood?

silky looking ice growing out of dead woodsilky looking ice growing out of dead woodSee more photos of hair ice on iNaturalist

In 2015, researchers from Germany and Switzerland published a very interesting (and highly readable for a scientific paper) study titled, “Evidence for the Biological Shaping of Hair Ice.” Through repeated observations and laboratory experiments, they confirmed that the biological action of a winter-active fungus, Exidiopsis effuse, is required to enable the growth of hair ice.

Looking at the cross section of a small branch, wood rays radiate from the center of a branch like spokes on a bicycle wheel. From these rays, hair ice threads emerge and grow perpendicularly from the wood surface. The thickness of individual hair ice stalks corresponds to the diameter of the wood ray channels. Perhaps for the first time in my life, I could visualize the true scale of these cellular channels.

But this doesn’t explain how the ice maintains its shape. Threads of hair ice are extremely thin, sometimes .02 millimeters in diameter or smaller. Yet, they can grow to be 20 centimeters long (that’s 1,000 times longer than it’s thickness!) and maintain their shape for days. Normally, ice this fine couldn’t retain its shape for so long. It would recrystallize into larger crystals quickly at temperatures near freezing.

While the chemical process that preserves its fine and delicate structure is not fully understood, it seems that the ice, according to the 2015 study’s authors, is “doped” into maintaining its shape by fungi. Samples of melted hair ice contain lignin, tannins, and other compounds. Lignin cannot be digested by animals, only by fungus and some bacteria. It’s presence in the water, therefore indicates fungal activity. (We can thank fungi that forested habitats aren’t buried in dead trees.) The lignin and tannins might act as a crystallization surface for the ice and the fungi might help to initially shape the ice as it forms at the surface of the wood rays.

When researchers applied fungicide or hot water (90-95˚C) the hair ice wood for several minutes, hair ice formation was suppressed for many days. Instead of hair ice, an simple ice crust formed on the wood. This indicates that hair ice formation is somehow catalyzed by fungal activity and that high temperatures inhibit the activity of Exidiopsis effusa.

Since I first observed it, air temperatures have been too warm in my neck of the woods for hair ice to reappear. Given its ephemeral nature and remarkable delicacy, I’ll be sure to search for it once the temperature drops again. If I find it, I’ll surely be astonished by ice that was—in a sense—doped by a magic mushroom.

Squirrels and Truffles

The forest is blooming with fungus in Lake Chelan National Recreation Area. Mushrooms are easy to find on the forest floor, but the mere presence of a few mushrooms does not reflect the abundance of fungus working under the soil, nor their importance.

On most of my recent hikes I’ve stumbled upon small excavations in the soil. Typically, the depressions are a few inches across and deep. Even though I haven’t witnessed the excavation in progress, just the end result, I suspect these are made by rodents searching for fungus in the soil. On the Lake Shore Trail, south of Stehekin, I found clue to support my hypothesis.

small hole in soil with fungus at bottom

The small depression next to the tip of my shoe contains a truffle.

Inside the hole was a truffle. Truffles are mychhorizal fungi. They do not photosynthesize, but these fungi are not parasites. They live in a symbiotic relationship with tree roots. Trees provide the fungi with sugar and the fungi provide trees with water and nutrients like phosphorus and nitrogen.

truffle in hand

This is the truffle at the end of the excavation. Over 350 truffle species in 50 genera inhabit the Pacific Northwest.

Truffles are highly sought after by fungal connoisseurs, human and rodent alike. They are especially important to flying squirrels, but rodents like flying squirrels are equally important to truffles. Unlike your typical toadstool, these underground fungus have no spore dispersal mechanism. They need animals to dig them up to spread their spores.

squirrel on tree

Northern Flying Squirrel (Glaucomys sabrinus), USFWS photo.

Flying squirrels, in particular, love truffles. Under the cover of darkness, flying squirrels find truffles by their odor, unearth them, and greedily devour them. Truffle spores are then distributed randomly and effectively in squirrel scat. For reasons unknown, my truffle was not harvested. Small rodents that eat truffles are preferred prey of owls and weasels. Was the excavator of this truffle snatched up by a unseen predator?

I don’t know the end to this particular story, but this is evidence of more than a rodent and hole. It symbolizes how predators need rodents; how rodents need fungi for food and trees for shelter; how trees need fungi for nutrients; how fungi need trees for sugars and rodents for dispersal. The tiny hole I found is more than superficial. It leads to a world of interdependence.


For more info on flying squirrels and truffles, check out Squirrels Cannot Live by Truffles Alone and Ties that Bind: Pacific Northwest Truffles, Trees, and Animals in Symbiosis.