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how trees get back to the ground

We’d been climbing steadily for three hours when I first noticed the sign board. The narrow grade we pedaled upon was a mostly mostly forgotten 4x4 road, and the eroding wooden kiosk seemed out of place. Its weary lettering announced that we had reached the end of the road, a statement in apparent contradiction to the road that lay just beyond it. Below the warning, a “special notices” section with a single bulleted point warned:

SPECIAL NOTICE: falling trees are always a hazard in the forest

This being the only special notice, I assumed it to be the most important and considered the message. A tree must get to the ground somehow, and falling seems like the standard method—but you’d have to be spectacularly unlucky to find yourself in the trajectory of a tree finding it’s way back to the ground. We continued, pushing our laden bikes, now wary of the sickly lodgepole pines that are ubiquitous in Colorado’s front range.  

Despite its questionable utility, the sign did have a good point. In 2013, during an immense flooding event thought to occur only once every 500 years, the road had been cleaved at the floor of the valley; swiftly removed by a landslide from high above. We continued through the pines into a clearing and found ourselves at a more definitive end to the road. What was once a winding mountain stream had become a steeply incised gulley, denuded of vegetation for some 40 feet on either side, and now flowing over bedrock at the bottom of the channel. The destruction was clear. So this was the end of the road. Perhaps it might be prudent to add another special notice to the sign: 

SPECIAL NOTICE 2: Every 500 years (or so) the top of the mountain will slide off, killing everything in its path, some probably by means of falling (projectile) trees. Avoid being here when that happens.

I wondered what it might have looked like to see the mountainside suddenly become liquified and accelerate downhill. I recollected a flash flood I had witnessed years prior, in a sandy creek bed in Utah. On a family trip, we were parked on the side of a road, enjoying lunch when I noticed a sound like someone raking leaves in a yard. Looking upstream, I saw a foaming mixture of branches, leaves, and mud—not more than a few inches high, but moving with a thickness wholly unlike water. It was less of a trickle and more reminiscent of lava flows I’d seen in documentaries. I would later hear that such flows were sometimes only fifteen percent water, the rest mud and anything else unlucky enough to be in the way. It quickly grew into a current. Had we been in any sort of canyon, the walls would have confined the torrent, increasing its depth and velocity into a deadly form. 

I stared up the steep, eroded, hill slope. Would land in the brink of a slide have any indication of movement? Would heavy rain be enough of a warning sign? On the scale of deadly geomorphic events, this slide seemed to fall somewhere between a flash flood and an avalanche—and having terrifying qualities of both. Standing in the notched channel, I thought about the sign we had passed; exactly when was the last time I took steps to protect myself from falling trees?

In some ways the best thing to do is to offload risk onto the experts. Trust the signs; pedal onwards more informed. We don’t have nearly as much trust for signs as we should, in the same way that we don’t trust experts any more. As a society we have moved away from expert opinion. 

Was the decrepit kiosk designed by a senior scientist at the Forest Service, or a summer intern? It could have been either, really. At any rate, they likely have more information than I do; forests are what they do. Still, falling trees? In fact, people are killed by falling trees. Just as they are killed by vending machines. Though, in both instances, it is not a spontaneous death. Walking through a forest is roughly analogous to shaking a vending machine, attempting to free its precious cargo. That is to say, neither the trees or the Coke-machine will come find you in your home, bursting the door to smother you in your sleep. We must accept some culpability, even if just for lusting too brazenly for a snack or some fresh air*. We are all risk takers, differing only in our motivations. In the case of trees, we are literally surrounded by danger—there are some 300 billion trees, just in the US! I had predictably and stupidly assumed that I must know better than a sign. 

Sometimes we trust crowd-sourcing more than the expert. It’s how we built such institutions as Wikipedia, and every 3.5 star restaurant review on Google maps. But we shouldn’t crowd-source the likelihood of a flood, or tree-death. The wisdom of the crowd is limited to the experience of the crowd, and most crowds haven’t been killed by trees. I’ve certainly never been killed by a tree. 

Ask the average person to estimate the probability of a catastrophic flood in any given year; I suspect it would be lower than the reality, by a wide margin-such a person has no frame of reference from which to evaluate unlikely events. Would a poll of 1,000 people converge on the right number? Not likely. Even the destruction wrought by a medium-sized landslide could be grown over in a decade. At that point, someone like myself could be forgiven for rolling up to the site of a catastrophic slide, and assuming that a tiny creek managed to remove stadium-loads of earth (and a road) via persistence and gumption.

“Not bad for a little guy, eh?” 

They/I would be wrong. 

This is not a controversial argument so much as it is a heuristic trap—one that I readily fall into. There is a very real limit to the ethos of skepticism, and there are real implications to ignoring the experts. This is an experience we are now living. A shocking amount of people have no ability to discern reliable information from ideology wrapped in the pretense of expertise. This is why people do silly things like refusing to don a face mask in the midst of a pandemic. It’s why we should trust the experts when it comes to low probability, high consequences events—like a pandemic. This is, of course, easier said than done; when was the last time you tested a smoke alarm in your house? The occurrence of a global pandemic has not surprised a single infectious disease expert, and yet, we all got hit by this “tree”. 

Later the next day, after descending our bicycles through the pines, we drove home along a canyon whose granite outcrops were marred by the same flood. Trees corpses were still piled high on banks, seven years later. Soon it will be forgotten—at least by the non-flood experts among us.

As always, this piece is unsubstantiated and sold as-is, so don’t bother emailing me about my punctuation. 

Recommended Reading:

The Control of Nature  by John McPhee