The Living Rotting Log: An Amazing Diversity of Fungal Life

by Jan Thornhill

The Maple Log 

I was out in the woods a few days ago on a mission—to find enough chanterelles for dinner. My plan was to go in and out as efficiently as possible. No dilly-dallying. No distractions. No paying attention to weird little things. But then I spied a curious little something on a rotting maple log. Closing in on it, I noticed another little something nearby. And then a big something. And then something else. So much for chanterelles for dinner.

The cup fungus, Humaria hemispherica, is hairy on the outside.

These tiny fuzzy cyphelloid cups, Flagelloscypha minutissima, are
less than a millimetre wide and are more closely related to
gilled mushrooms than to the Humaria cup above.

I kept finding things on this log that's been lying on the ground for possibly four or five years. As I continued to add specimens to my basket, I was reminded of an interesting paper that came out of Sweden in 2012. Researchers there had drilled out multiple samples from Norway spruce logs in two separate locations, and at different stages of decay. They carted these sawdust samples off to the lab where DNA was extracted. In the 38 logs studied, they found evidence of almost 2,000 species of fungi. One log harboured an astonishing 398 different species!

Trichaptum biforme is a common hardwood polypore.

This polypore, Inonotus glomeratus, which can be both parasite and
wood decomposer, probably contributed to the death of this maple.

Inspired, my mission changed from finding food to finding as many species as I could on the log, like a mini mycological bioblitz. Of course I wasn't delusional enough to think I would find anywhere near as many species as the Swedish researchers had in their lab. Unlike the researchers with their DNA sequencing, I was limited to collecting only what I could see with my naked eye—the spore-producing fruiting bodies of wood-inhabiting species. Invisible to me was what was going on inside the log, the strands of mycelia of who-knows-how-many other species that might have produced fruiting bodies earlier in the season, or that might do so later. 

Scutellinia or Eyelash Cups are common orange or red discs with dark-haired edges.

Chlorocyboria species are blue-green and stain wood the same colour.

A Succession of Decomposers

In the life of a rotting log, (which, for a large maple like the one I was exploring, can take twenty years to completely decompose into forest soil), there is a succession of different fungi that do the decomposing. These species arrive as wind- or insect-borne spores, or as already growing mycelia that creep into the log from the forest floor. Some of the earliest colonizers may have caused or contributed to the death of the tree. Some, though not pathogens, may have already spread extensively through the dead wood of the tree before it crashed to the ground. Others don't get a foothold until the log has spent several years absorbing moisture from the forest floor. Still others wait until the early decomposers have changed the structure of the wood or its chemical composition. Some, though their mycelia has crept for years through the heartwood, may never actually produce fruit—the mushrooms, crusts, cups, or shelf fungi we can see. 

These Mycena mushrooms were tiny and fragile.

Cyptotrama asprata is a brightly coloured wood decomposer with white gills.

I got intimate with this log for an hour, kneeling and squatting, (and swatting away crowds of relentlessly aggressive mosquitoes), while taking pictures and carving off samples. When I was done, I had a basket full of polypores and toothy crusts, cups and saucers, and a few complete mysteries. I even had a nice selection of actual mushrooms with gills. The basket wasn't heavy. Many of the things I found were tiny, as in only a millimetre or two in size. 

This Bleeding Foot Mycena mushroom has been attacked
by a parasitic Spinellus fusiger mold.

Fuzzy Chromelosporium fulvum is the asexual anamorphic form of a cup fungus. 

39 Species!

Half of my finds needed microscopy and books and the internet to nail them down to species. I've now spent three days at it and my final number of identified fungi species is 32. Most are saprophytes, or wood decayers. Several are parasites, including a mold that attacks small mushrooms. At least one is an anamorph, or asexual form of a completely different looking fungus. I also brought home 7 different myxomycetes, or slime molds, which are unrelated to fungi, but which we fungi fanatics always include in our collections (read about these fascinating guys here)—which brings my grand total to 39 species. Not too shabby!

I found 7 different slime moods, including a Lycogala, or Wolf's Milk
Slime (above) and Ceratiomyxa fruiticulosa, or Coral Slime (below).

But now I'm hooked, and I know I'm going to have to regularly visit this log, and keep a running inventory of the progression of species I find on it during its long journey from recently fallen tree to forest soil. It will be a slow project, but it will be fun, exploring the teeming life on this dead tree.  

Related Reading: 

Discover Magazine's excellent article What Lurks in Logs
My blog post about animal decomposition

Reference:

A. Kubartová et al. (2012). Patterns of fungal communities among andwithin decaying logs, revealed by 454 sequencing. Molecular Ecology, 2:18

A Tribute to Scavengers and Decomposers

by Jan Thornhill

I visited a school a few days ago to talk about my books and, as usual, passed around the contents of my “museum-in-a-bag,” a collection of, among other things, skulls, dinosaur bones, desiccated insects, snake skins, feathers, and a mummified bat and two hummingbirds. The children are always very careful with my treasures, but that day my white-tailed deer skull finally snapped in half. I wasn’t exactly surprised, since this particular skull has been handled by at least 5,000 kids over the past few years. Besides, I can always glue it back together again. I’d like to save it, though, because, like many of the things in my bag, the deer skull has a story.

White-tailed deer skeleton (Jan Thornhill)

I found it, along with most of the rest of the deer’s skeleton behind a fence on my road. It’s not hard to imagine how the animal died: I’m sure someone struck it by accident with their car. Though mortally injured, it must have managed to make two great bounds, one to get off the road and the other to get over the fence. The person who hit it must have been relieved to see it disappear into the brush as he or she drove away. But then, alone, the deer collapsed and died.

A year earlier, I had looked for puffballs in exactly the same spot in late autumn. There were no deer remains then, so the longest it could have been hidden there was twelve months. Amazingly, other than a few wisps of hair and a couple of snippets of dried skin, the skeleton was completely clean – clean enough that I had no qualms about bringing it home.

So who do I have to thank for cleaning those bones for me? Scavengers and decomposers, that’s who – my favorite characters in the food chain.

I was quite sure a coyote must have visited the corpse of the deer shortly after it died since the bones of two of its legs were missing. The coyote is the only animal in my neighborhood that is strong enough to drag away such large parts. Though they’re predators, and often hunt for food, coyotes are also such frequent scavengers that they’ve developed a special receptor in their brains that makes them immediately throw up anything that is dangerously rotten. So a coyote wouldn’t have had to feed on the carcass immediately, especially if the deer had died in the cold of winter.

Coyote feeding on elk carcass (Courtesy Bryan Harry, U.S. Fish & Wildlife Service)

Turkey vulture

Other scavenging mammals, such as foxes and skunks, might also have visited the corpse, as well as birds, such as crows and vultures. Our local turkey vulture is one of the few large animals that is a dedicated scavenger, which means that its only food is carrion, or already dead or decaying flesh. They’re perfect for this job: they have an extremely well-developed sense of smell that allows them to home in on food that's miles away; their bald heads reduce the amount of rotting matter that might stick to them; strong acids in their digestive tracts destroy harmful bacteria; and their urine is also very acidic – and here’s the best part – so they pee down their legs to let the acid destroy nasty bacteria clinging to them. 

As well as being fed upon by these larger animals, in the warmer months corpses attract an amazing number of insects. A variety of flies are lured by the smell of death and lay their eggs. Their larvae, or maggots, are voracious carrion feeders. Flesh-eating beetle larvae continue the job and, later, other beetles with specialized mouth parts show up to feast on tough skin and ligaments, followed by moths that eat fur and hair. These insects all arrive at such specific stages of decomposition that forensic entomologists, scientists who study the insects that are found on or near dead things, can use their knowledge of this progression to determine the time of death when the remains of a human are found.

Close-up of a blowfly maggot (Eye of Science)

Throughout this whole process bacteria are active, gobbling up the corpse from within. These bacteria produce gases as a waste product, and it’s these gases that are responsible for the putrid odors that waft off rotting animals. Humans are naturally revolted by these smells, which is a good thing. If we weren’t disgusted by the smell of decomposition, we might be tempted to eat food that has gone bad and get sick from the bacteria growing on it. Interestingly, almost everyone in the world says the same thing when confronted by these smells, some version of “Yuck!” or “Ick!” This verbal gagging is so natural and so universal that some people think it might be the way that human language began.

My tip to anyone who finds an animal skull (or other bones) and wants to bring it home, is to use your eyes and nose. If it looks gross and smells disgusting, leave it where it is. Mark the location and return in a few months. More often than not, scavengers and decomposers will have completely cleaned it up for you.

You can find out lots more about death and decomposition in my book: I Found a Dead Bird: The Kids’ Guide to the Cycle of Life & Death (Maple Tree Press)

Here’s a fun, time-lapse video showing a watermelon decomposing over 35 days: http://thekidshouldseethis.com/post/12926682492