It is early spring and I’m walking through one of my favourite woodlands in Ontario’s Carolinian forests. The river that had swollen with snow melt just a week before, now flows with more restraint. I can see the cobbles and clay of scoured banks under the water. Further on, part of the path along the river has collapsed from a major bank scour the previous week. The little river is rather big and capricious, I ponder; then I consider that the entire forest sways to similar vagaries of wind, season, precipitation and unforeseen events. Despite its steadfast appearance the forest flows—like the river—in a constant state of flux and change, cycling irrevocably through life and death.
I walk slowly, eyes cast to the forest floor thick with dead leaves, and discover seeds and nuts—the promise of new life. I aim my gaze past trees and shrubs to the nearby snags and fallen logs. I’m looking for hidden gifts. One fallen cedar log reveals swirling impressionistic patterns of wood grain, dusted with moss and lichen. Nature’s death clothed in beauty.
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Cedar log showing patterns of wearing and decay, Little Rouge Woodland, ON (photo by Nina Munteanu)
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The bark of a large pine tree that has fallen is riddled with tiny beetle holes drilled into its bark. Where the bark has sloughed off, a gallery of larval tracks in the sapwood create a map of meandering texture and colour.
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Larval tracks on pine wood, Little Rouge Woodland, ON (photo by Nina Munteanu)
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Nearby, another giant pine stands tall in the forest. Its roughly chiseled bark is dusted in lichens, moss and fungus. The broad thick ridges of the bark seem arranged like in a jigsaw puzzle with scales that resemble metal plates. They form a layered mosaic of copper to gray and greenish-gray. At the base of the tree, I notice that some critter has burrowed a home in a notch between two of the pine’s feet. Then just around the corner, at the base of a cedar, I spot several half-eaten black walnuts strewn in a pile—no doubt brought and left there by some hungry and industrious squirrel who prefers to dine here.
The forest is littered with snags and fallen trees in different stages of breakdown, decomposition and decay. I spot several large cedar, pine, oak and maple snags with woodpecker holes. The snags may remain for many decades before finally falling to the ground.
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When Woody Material Decomposes
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The forest ecosystem supports a diverse community of organisms in various stages of life and death and decay. Trees lie at the heart of this ecosystem, supporting a complex and dynamic cycle of evolving life. Even in death, the trees continue to support thriving detrivore and saprophytic communities that, in turn, provide nutrients and soil for the next generation of living trees. It’s a partnership.
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Rotting maple tree, showing various stages of decay, Little Rouge Woodland, ON (photo by Nina Munteanu)
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Decomposition and decay are the yin to the yang of growth, writes Trees for Life; together, they form two halves of the whole that is the closed loop cycle of natural ecosystems.
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Snags and rotting logs on the forest floor provide damp shelter and food for many plants, animals, and other life. Most are decomposers, including earthworms, fungi, and bacteria. As the wood decays, nutrients in the log break down and recycle in the forest ecosystem. Insects, mosses, lichens, and ferns recycle the nutrients and put them back into the soil for other forest plants to use. Dead wood is an important reservoir of organic matter in forests and a source of soil formation. Decaying and dead wood host diverse communities of bacteria and fungi.
Wood tissues of tree stems include the outer bark, cork cambium, inner bark (phloem), vascular cambium, outer xylem (living sapwood), and the inner xylem (non-living heartwood). The outer bark provides a non-living barrier between the inner tree and harmful factors in the environment, such as fire, insects, and diseases. The cork cambium (phellogen) produces bark cells. The vascular cambium produces both the phloem cells (principal food-conducting tissue) and xylem cells of the sapwood (the main water storage and conducting tissue) and heartwood.
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Stages of Decay
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Forest ecologists defined five broad stages in tree decay, shown by the condition of the bark and wood and presence of insects and other animals. The first two stages evolve rapidly; much more time elapses in the later stages, when the tree sags to the ground. These latter stages can take decades for the tree to break down completely and surrender all of itself back to the forest.
A fallen tree nurtures, much like a “mother” archetype; it provides food, shelter, and protection to a vast community—from bears and small mammals to salamanders, invertebrates, fungus, moss and lichens. This is why fallen trees are called “nursing logs.”
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The Succession of Decomposition & New Growth
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I stop to inspect another fallen tree lying on a bed of decaying maple, beech and oak leaves. When a fallen tree decomposes, unique new habitats are created within its body as the outer and inner bark, sapwood, and heartwood decompose at different rates, based in part on their characteristics for fine dining. For instance, the outer layers of the tree are rich in protein; inner layers are high in carbohydrates. This log—probably a sugar maple judging from what bark is left—has surrendered itself with the help of detrivores and saprophytes to decomposition and decay. The outer bark has mostly rotted and fallen away revealing an inner sapwood layer rich in varied colours, textures and incredible patterns—mostly from fungal infestations. In fact, this tree is a rich ecosystem for dozens of organisms. Wood-boring beetle larvae tunnel through the bark and wood, building their chambers and inoculating the tree with microbes. They open the tree to colonization by other microbes and small invertebrates. Slime molds, lichen, moss and fungi join in. The march of decay follows a succession of steps. Even fungi are followed by yet other fungi in the process as one form creates the right condition for another form.
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Most hardwoods take several decades to decompose and surrender all of themselves back to the forest. In western Canada’s old growth forest, trees like Western redcedars with their high resin content can take over a hundred years to decay once they’re down. The maple log I’m studying in Ontario’s Carolinian forest looks like it’s been lying on the ground for a while, certainly several years. The bark has fragmented and mostly fallen away, revealing layers of sapwood in differing stages of infestation and decay. Some sapwood is fragmented and cracked into blocks and in places looks like stacked bones.
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Decomposition by Shapeshifting Fungi
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Black lines as though drawn by a child’s paintbrush flow through much of the sapwood; these winding thick streaks of black known as “zone lines” are in fact clumps of dark mycelia, which cause “spalting,” the colouration of wood by fungus. According to mycologist Jens Petersen, these zone lines prevent “a hostile takeover by mycelia” from any interloping fungi. Most common trees that experience spalting include birch, maple, and beech. Two common fungi that cause spalting have colonized my maple log. They’re both carbon cushion fungi.
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Spalting by carbon cushion fungi on an old maple log, Little Rouge Woodland, ON (photo by Nina Munteanu)
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Brittle cinder (Kretzschmaria deusta) resembles burnt wood at maturity. Deusta means “burned up” referring to the charred appearance of the fungus. Hypoxylon forms a “velvety” grey-greenish cushion or mat (stroma). As the Hypoxylon ages, it blackens and hardens and tiny, embedded fruiting bodies (perithecia) show up like pimples over the surface of the crust.
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Hypoxylon forms a cushion on decaying wood, Little Rouge Woodland, ON (photo by Nina Munteanu)
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Much of the exposed outer wood layer looks as though it has been spray-painted with a green to blue-black layer. The “paint” is caused by the green-stain fungus (Chlorociboria) and blue-stain fungus (Ceratocystis). The blue-green stain is a metabolite called xylindein. Chlorociboria and Ceratocystis are also spalter fungi, producing a pigment that changes the color of the wood where they grow. While zone lines that create spalting don’t damage wood, the fungus responsible most likely does.
Spalting is common because of the way fungi colonize, in waves of primary and secondary colonizers. Primary colonizers initially capture and control the resource, change the pH and structure of the wood, then must defend against the secondary colonizers now able to colonize the changed wood.
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References:
Boberg, J., 2009. “Litter decomposing fungi in boreal forests.” Swedish University of Agricultural Sciences, Uppsala, Sweden.
Buczacki, S., 1989. “Fungi of Britain and Europe.” Collins, London.
Coleman, D.C., Crossley Jr., D.A., Hendrix, P.F., 2004. “Fundamentals of Soil Ecology.” Academic Press, Burlington, Massachusetts.
Munteanu, Nina. 2013. “The Ecology of Story: World as Character.” Pixl Press, Vancouver.
Packham, J.R., Harding, D.J., Hilton, G.M., 1992. “Functional ecology of woodlands and forests.” Springer.
Resh, V.H., CardÃ, R.T., 2009 . “Encyclopedia of insects.” Academic Press, Burlington, Massachusetts.
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Nina Munteanu is a Canadian ecologist / limnologist and novelist. She is co-editor of Europa SF and currently teaches writing courses at George Brown College and the University of Toronto. For the lates on her books, visit www.ninamunteanu.ca. Nina’s bilingual “La natura dell’acqua / The Way of Water” was published by Mincione Edizioni in Rome. Her non-fiction book “Water Is…” by Pixl Press (Vancouver) was selected by Margaret Atwood in the New York Times ‘Year in Reading’ and was chosen as the 2017 Summer Read by Water Canada. Her novel “A Diary in the Age of Water” was released by Inanna Publications (Toronto) in June 2020. You can read her just released eco-fiction thriller Gaia’s Revolution by Dragon Moon Press.
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The Meaning of Water 