What party you ask? The one in the forest of course, which couldn’t roll on without a regular supply of dead and dying trees.
“The truth is, the system depends on the death of trees…” Torolf Torgerson, Research Entomologist – US Forest Service
How many forest residents do you think really depend on dead and dying trees? Make a mental list … 10 species, 20 ? I’ll bet it’s way more than anyone might think. Just for starters – all species of woodpeckers, flying squirrels, bats, cavity nesting birds like Chickadee and Tufted titmouse, wrens seeking food, bears seeking food, salamanders, skinks, nesting owls, snakes, hibernating Box turtles, mice, voles, sleeping raccoons, nesting Wood ducks – not to mention the innumerable decomposers at the heart of it all that are food for the rest of the crew.
Though our forest can be considered degraded in many ways, by one measure at least we score high – the vast quantity of what forest scientists term “CWD”, or coarse woody debris. Whether from windstorm or disease or plain old age, the number of toppled and decaying trunks is quite astounding (leading some visitors to wonder why we don’t clean the place up and sell that wasted timber!). We are actually quite rich, with a vast bank of stored nutrients to feed the future forest.
These masses of woody debris give rise to an amazing microbiotic community that supports the more visible species. Diseased and damaged standing trees are valuable too – woodpeckers need at least three kinds. Living trees with decaying heartwood to excavate nest holes, trees with dead tops for drumming, and trees with decay near the ground that harbor carpenter ants.
As with a new housing development, a whole network of life arises adjacent to and within the fallen tree. The various fungi and pair of colorful millipedes in the pic above live under a piece of rotting log.
The tangle of fallen trunks in the pic below becomes a vibrant city of Five lined skinks in the summertime. On a hot day there is an audible rustling as one approaches it, the sound of many skinks running for cover. Orange throated males patrol the tops of the logs, females lie deep within coiled around their eggs.
The pic above is an enlarged section of the stump below, which is leaking fine reddish humus as it’s slowly being dismantled. Forest scientists use a classification system for dead trees, based on their level of decay and colonization by other species. A dead but undecayed tree is class 1; by the time it’s an overgrown tree-shaped pile of humus, it will be class 5. In between these extremes, class 4 is the sweet spot for life. The bark and sapwood have sloughed off, and what’s left is quite porous and tunneled out. But the heartwood is still relatively stable, supporting a labyrinth of passageways.
In a class 1 tree, woodboring beetles first breach the intact tree bark with their small exit holes, then woodpeckers carefully chisel larger openings seeking the larvae. Both create entry for organisms as diverse as fungi, voles, cavity nesting birds and raccoons – none of which can make their own holes. Fungi in particular quickly speed up decomposition, with their unique ability to break down lignin.
Our resident Pileated woodpeckers have a very specific interest in deadwood – it’s where tasty Carpenter ant colonies are found. Armed with a formidable icepick of a beak, this largest north american woodpecker demolishes rotten logs ands stumps, and can even dig deep into the heart of living trees.
The trunk below is between class 4 and 5, as its lower part morphs into a rich pile of humus. One of my lasting nature memories from childhood was discovering the lovely feel and smell of humus forming at the base of an old tree. On our forest hikes when I give kids a small handful of this “almost soil”, a surprising number of them respond with reverence, even wanting to take some home in their pocket! Usually they just carry it a short way and drop it. And I tell them they’re helping to spread the wealth.
One thought on “Dead trees – the life of the party, march 20”
These periodic notes provide just enough biology lessons that I can take in small bits and absorb them. Thank you, Rosemary!