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