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The Other CWD

This winter we've had a number of projects going on necessitating the removal of lots and lots of trees and shrubs, both big and small.

We had a very successful honeysuckle hunt, with the slain carcasses consolidated into a few piles in the Osborne woods. We had a professional logging crew clear about three acres from the pine plantation south of the nature center for the future campground.

We removed several large ash trees in varying, but irreversible, states of decline from emerald ash borer infestations. And the last, biggest project (for us, anyway; the loggers had a big job on their hands in the pine plantation) took place along Hwy 13, where we did some clearance for a power line set to be installed sometime this year.

Understandably, it always raises some eyebrows from the public when we cut trees, and the trees along Hwy 13 probably raised them the highest. For just a little context, our stand map and stewardship plan for Osborne's forest inventory has a few spots targeting the creation of early successional habitat.

It just so happened that the trees along Hwy 13 were among those stands slated for the kind of short-interval clearcutting that maintains shrubby, dense-cover early successional forest. So it was an opportunity to tackle some trees that I wasn't sure how to approach with the highway nearby, as we were able to get some assistance closing lanes from the Iowa DOT for the project.

The tree stumps will be allowed to resprout and sucker to their rootstocks' content, and with the preponderance of fast-growing dogwood and aspen up there I suspect we'll have that shrubby-sheik appearance that's all the rage amongst wandering teenage grouse by this time next fall.

All of these projects have me thinking about CWD. Not chronic wasting disease, but the other CWD, coarse woody debris.

The good kind of CWD

Most folks with a little environmental knowledge appreciate that dead wood provides value to the woodland habitat. It's self-evident in the shredded excavations from pileated woodpeckers, the middens of hackberries cached inside them by chickadees, and the streaking patterns of fungi and beetle galleries on the heartwood as the bark falls away.

Pileated woodpecker excavation

But with so much coarse woody debris on site, my curiosity kicked in and I decided to do a little more research on what other kinds of value a tree brings to the ecosystem after its growing life ends.

Turns out, the benefits of CWD to forest health go far beyond woodpecker and insect habitat, or brush piles suitable to raise a new generation of rabbits. Perhaps most astoundingly, a lot of research suggests that the trees actually have more "life" inside them after they die.

Depending on the geographic region, large downed trees can have anywhere from twice to four times as much biomass as they had in life. Which seems impossible, until you consider the tree's life.

Each and every day, a tree has to fight off insect, fungal, and bacterial invasions. But in death, those agents all find themselves bellied up to a defenseless buffet. So what used to be relatively sterile heartwood becomes colonized by ants, dozens of species of beetles, fungi, bacteria, and even vertebrates like salamanders (who actually make up, by far, the highest percentage of vertebrate biomass in our forest ecosystems at dozens to hundreds of individuals per acre), shrews, and birds who come to feed on the decomposers.

Suite of fungi & mosses on an old elm

For a large tree, this buffet can last for decades or even centuries. Each tiny critter turns a little bit of tree into body mass in its own life cycle, and a little bit into poop that fertilizes the area around the dead tree.

This adds significant weight to the importance of big, mature trees in combatting climate change. I confess, I didn't always understand why climate scientists seem more concerned with preserving old-growth forest than planting new trees (though, to be sure, they usually advocate for both). My rationale? As a tree matures, its ability to take up new carbon decreases, and of course stops entirely once the tree dies. A growing tree on the other hand gobbles up carbon most voraciously. I understood that big trees had taken up a lot of carbon over their lives, but I thought most of it would simply be released as natural decay once the tree died. So wouldn't lots of vigorously growing trees do better than old, declining ones?

But I was missing a big variable. In reality, most of that carbon actually gets converted into other biomass. And once all that insect frass and fungal hyphae and pruned roots get incorporated into the soil, that carbon remains sequestered for a very long time. Even the above-ground portion remains in the ecosystem, rather than the atmosphere, until long after the tree becomes humus.

The tree dies. An ant colony moves in. A salamander eats the ants. A snake eats the salamander. A hawk eats the snake. Shin bone's connected to the knee bone. You get the idea.

Tiger salamander on CWD

Along the edges of the rotting log, a tiny seedling sprouts. Its early life is a sheltered one, protected from the wind and undetected by herbivores. The spongy deadwood, perforated by beetles and holding water between rainstorms, creates a microclimate of higher humidity. The peeling bark provides a steady influx of nutrients to its developing roots like an IV drip.

Trees growing from a "nurse log" in Bartlett Cove, AK (photo from the National Park Service)

By the time that seedling matures, the nurse log is long gone, but this tree stands high above others of its same generation who landed in a less fortunate spot. After a few decades or centuries, a stand of trees with unusually good vigor have formed linearly in a seemingly random patch of the forest.

Ecologists call this a "legacy effect," wherein past processes inform current conditions. Of course, that legacy continues when these larger, healthier trees meet their own end and start the cycle anew.

We struggle to recognize this legacy when we see it due to the limitations of our time scale. I hear from landowners frequently who say their woods is full of "junk," and they need to "clean it out," meaning dropping or removing or piling and burning all the dead wood. I don't own my own timber, but I have certainly had these same thoughts exploring other tracts of forest.

But the healthiest forests - at least, healthiest measured by biodiversity - have plenty of dead wood both standing and on the ground. More than we're used to, in fact. Many forests with which we're most familiar are planted, or managed for specific purposes, or relatively new on ecological scales.

That means they simply haven't had the time to develop a full inventory of dead wood that would occur in a forest that has had centuries to build up. An "old growth forest," in the technical sense, is dominated by trees beyond 120 years old. In Iowa, that means they had to escape axes, matches, cows, and plows at a time when not many trees did.

Almost-old growth at Bloody Run Wildlife Area

That approach to a new equilibrium looks so unusual to us we interpret it as a forest health issue, rather than a natural part of the successional dynamics. In other words, our own perception is suffering a bit from a psychological and emotional legacy effect.

We also have our own habitat requirements to consider. It's not always going to be tolerable to have big slash piles rotting indefinitely, and in our fire-adapted woodlands the picture changes considerably where the legacy might have been a little more short-lived.

Burning slash from a recently-cleared fenceline at Osborne

But it's food for thought. How much dead wood can you live with in your timber? Do you actually need to get rid of it, or do you just find it unsightly? Can you enjoy your woods by adjusting your perception a bit, taking a moment to appreciate all the life borne of the death of a big tree? Which do you value more, a diverse habitat or an easy walk on a Sunday afternoon? Both value systems have merit, but only when we can understand both sides.

Looking Back

March can often be a slower time around these parts. Often too early for burning, usually too late for forestry work, and too iffy weather-wise for much public programming. This March, that was not the case.

Our O.W.L.S. program got up and running for 2023 with naturalist Abbey hosting a talk on Iowa's extirpated large predators here at the Osborne Nature Center. The group enjoyed a great deal of camaraderie during and after the program with a potluck lunch. We hosted the 7th, and by far the coldest, running of the Motor Motor Trail Races. Despite the conditions we had an incredible turnout. It may or may not have taken 48 hours for those of us not running to regain feeling in our toes but as always, it's worth it.


Between those programs, we spent a lot of time on the aforementioned tree clearing projects, while contract crews toiled away on the renovations of the Motor Mill Inn. It's fascinating to watch the progress unfold and hard to believe we're nearing the finish line on this longstanding dream of the CCCB and Motor Mill Foundation.

Work in progress at the Inn

Looking Forward

Now we're talking hectic. The last few classroom programs are winding down, the grass is greening up, our campgrounds will soon have the water turned back on, and we're anxiously watching the weather to find the right time to put prescribed fire on the ground. We'll also be ramping up the field trip season, and shuffling in a few public programs as well. The O.W.L.S. will roost again at the Osborne Nature Center on Thursday, April 20th at 11:00 AM for a peek into including a hike to visit the pasque flowers at the Motor Mill Historic Site on Friday, April 21st at 5:00 PM. The hike is off trail, and up a fairly rugged slope so come prepared!

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