The Tree Spirits
A glowing log, a badly timed lantern, and a tree with a remarkably busy afterlife.
Otto found a fallen tree glowing green in the dark, which is a reasonable thing to investigate. He labeled it “tree spirits” before examining any of it, which is where Echo registered a concern.
“Put a question mark after that.”
Then Otto switched on his lantern to get a better look, and his evidence vanished.
For someone conducting a supernatural investigation, this is alarming. For the raven watching him operate the lantern, it is fairly straightforward.
What Otto has found is foxfire: faint light produced by certain fungi growing in decaying wood. The glow can be subtle enough to escape notice until the surroundings are dark and your eyes have adjusted. A familiar fallen trunk suddenly appears to have acquired an opinion about being dead. University of Georgia: Fox-fire makes forests glow.
Why the lantern hid the glow
Otto’s lantern overwhelms that faint light. It can also make his next attempt to see it more difficult.
For us, vision in dim conditions depends heavily on rod cells in the retina. Their sensitivity increases as we spend time in darkness, with substantial adjustment continuing over tens of minutes. Bright light can interrupt that process; how much depends on its intensity and duration. There is no universal reset button triggered by a single glance at a phone.
Very faint objects may also be easier to detect when you look slightly beside them, directing their image toward a part of the retina richer in rods. That technique, called averted vision, can help when a dim patch seems to fade under a direct stare. Webvision: Light and Dark Adaptation.
Otto had to stop illuminating the forest for a moment to notice what it was already doing.
The fungus behind the foxfire
Once the light becomes visible again, his investigation moves beneath the bark.
A wood-decaying fungus grows through its food as fine threads called hyphae. Together, those threads form mycelium. A mushroom is a reproductive structure that some fungi produce; much of the organism can remain hidden within the wood.
In Armillaria, the honey fungus group, the mycelium can glow while mature mushrooms remain dark. That makes glowing wood possible even when no mushroom is visible. Other luminous fungi do produce glowing mushrooms, so the source of the light depends on the species. Research on bioluminescence in Armillaria and related fungi.
The chemistry is a discovery worthy of Otto’s notebook. In luminous fungi, an enzyme called luciferase helps a molecule called luciferin react with oxygen, releasing energy as light. Researchers identified the fungal luciferase and other key enzymes in this system in 2018. The pathway builds the light-producing molecule from caffeic acid, a widespread natural compound, and includes a route for recycling the spent product. Research on the fungal bioluminescence system.
There is enough happening inside that little green patch to keep Otto talking well past bedtime.
Why glow at all?
Why fungi glow is a harder question, and one worth leaving a question mark beside.
A 2015 study of the Brazilian fungus Neonothopanus gardneri found that its light production follows an internal daily rhythm. The researchers also placed artificial mushrooms in its habitat, illuminating some with green LEDs and leaving others dark. The illuminated models attracted more insects, including beetles and flies.
Those results support the idea that light can recruit visitors that might carry spores. The experiment demonstrated insect attraction; it did not establish successful spore dispersal or a universal explanation for fungal light. In particular, we cannot assume that glowing mycelium inside Otto’s log serves the same purpose as a luminous mushroom exposed above the forest floor. Oliveira and colleagues, Current Biology.
Echo’s recommendation about punctuation continues to hold up.
“The afterlife has tenants”
Meanwhile, Otto has begun finding residents.
A beetle crosses the bark. A salamander looks out from a crevice. These encounters move the story from the chemistry of a glowing fungus to the ecology of the wood around it.
“The afterlife has tenants.”
Wood decay is active biological work. Specialized fungi break down the materials that give wood its strength, gradually changing its structure and contributing to forest litter, soil organic matter, and other products of decomposition. The softened wood becomes part of a changing habitat. US Forest Service: Wood Decay.
The salamander makes that habitat especially tangible. Pacific Northwest woodland species such as ensatinas and western red-backed salamanders are lungless. Gas exchange through their moist skin makes them vulnerable to drying out, and cool, damp refuges matter to their survival.
Decaying logs can provide those refuges. In an Oregon Coast Range study, temperatures inside logs and soil remained below critical thermal limits for these salamanders even when summer air temperatures approached or exceeded them. A sheltered space beneath the bark can offer a very different set of conditions from the exposed air nearby. Research on downed wood and salamander habitat.
Otto sees a small animal with a good hiding place. The animal has found somewhere it can keep being a salamander.
Nurse logs and the next forest
Then come the seedlings.
On a forest floor crowded with ferns, moss, and litter, a small seed can have a difficult start. A decaying log may offer an elevated seedbed, retained moisture, and softened wood that roots can enter. As decomposition proceeds, nutrients also become available. A fallen trunk supporting new plants is known as a nurse log. National Park Service: Nurse Log in Bartlett Cove.
The young trees are separate individuals that have established themselves on the old trunk. Their roots can eventually reach the soil beneath it. In the temperate rainforests of the Pacific Northwest, western hemlock and Sitka spruce are familiar participants in this process.
Sometimes the arrangement remains visible long after the nurse log has disappeared. Seedlings established along its length become a row of larger trees. Their roots reach around the old trunk, leaving arches or gaps as the wood beneath them decays. Such rows are called colonnades. Olympic National Park describes them as one of the recognizable features of its temperate rainforests. National Park Service: Temperate Rain Forests.
An absent tree can still be traced in the spacing and roots of the trees that grew along it.
For a story called The Tree Spirits, that is a particularly satisfying discovery.
Looking for foxfire—and its daytime clues
You can look for this part in daylight: seedlings along a mossy trunk, roots reaching around decaying wood, or a row of older trees whose shared beginning has almost vanished.
If you also hope to see foxfire, look for naturally exposed patches of damp, decaying wood on a dark evening. Keep a light for walking; once settled safely in place, switch it off and give your eyes time. Expect something much fainter than the green in the comic. Suitable wood and darkness improve the opportunity, but a sighting is never guaranteed. University of Georgia.
Leave the bark attached and the log where it is. The residents have already arranged everything to their liking.
Becoming the forest
By the last panel, Otto’s notebook is closed. He has an explanation for the glow, a closer look at the tenants, and two small trees to think about. Echo is still beside him.
“So the tree isn’t haunting the forest,” Otto says. “It’s becoming the forest.”
“With mood lighting.”