Tree trunks, game theory, and the invisible hand

Image: Me, collecting foliage from balsam fir trees in Quebec.  Photo courtesy Cameron Rugo.

Last month I spent a week in the field, as part of a team collecting soils and foliage for a project assessing carbon sequestration in spruce budworm-defoliated forests*. The soil was always easy to reach, conveniently located right at ground level (funny how that works, isn’t it?) – but the foliage, not so much. As is true in forests the world around, the bulk of the foliage is way, way up in the air. That pole I’m wielding in the photo above? It’s a “pole pruner”, and it has a cutting head at the end of a series of interlocking pole segments – seven segments in the photo, which means I’m balancing a wobbly, bendy pole and manoeuvering it through snags and branches to snip samples about 12 metres (40 feet) from the ground. This is hard, and as I was doing it I found myself thinking that the whole thing would be simpler if the trees could just get their act together and grow at bush height.

Now, that’s pretty stupid thing to think, I admit; but it’s also an interesting thing to think. Trees are tall only because they’re caught in an unfortunate bit of game theory. A single tree growing by itself will be best served by sprawling, not reaching for the sky. A sprawler can harvest light without investing resources in a trunk and in the machinery and energy to lift water and nutrients up that trunk, and without running the very substantial risk of wind sending the whole thing crashing to earth. The only reason for a tree to grow up – the only reason for it to have a trunk at all – is that the other trees around it are growing up, too; and a tree that doesn’t grow up will be overtopped and shaded out by the trees around it. All the trees would be better off if they could somehow all sign a treaty (a treety?) agreeing to cap their height. Without that treaty, what’s best for each individual (to grow up) leaves every individual labouring, inefficiently and unnecessarily, to photosynthesize atop a stilt. The problem is this: natural selection can optimize a lot of things, but it takes special circumstances for it to evolve cooperation that depends on restraint**.

But of course, it isn’t just tree that have trunks, because the same bit of game theory applies to us too. The world’s enormous, many-times-overkilling nuclear arsenals are tree trunks (and we have nuclear-arms pacts in an attempt to shorten them). The financial incentives local governments offer to get a new factory to set up in their jurisdiction instead of another one are tree trunks too. So are the hospital advertisements that puzzle Canadian visitors to the United States – and along with them, the oversupply of medical specialists and the enormous bleed of resources to private health-insurance administration. And increasingly, our carbon emissions are tree trunks, as each country refuses to apply tough-enough carbon taxes*** because all the others won’t. Tree trunks are everywhere, and they make clear the frequent failures of Adam Smith’s famous invisible hand. Perhaps “Game Theory for Libertarians” would be a useful college course.

You know, they probably shouldn’t let me out in the forest. I think weird thoughts out there.

© Stephen Heard September 11, 2018


*^It’s completely irrelevant to today’s post, but in case you’re interested: spruce budworm is a moth that undergoes spectacular population outbreaks every 40 years or so across much of northeastern North America. When outbreaks peak, the caterpillars are voracious and can strip the new foliage from fir and (to a lesser extent) spruce trees over millions of hectares of forest. Here’s a branch sampled from a defoliated stand, and a normal branch:

Loss of needles impairs tree growth and, after a few years, can kill trees. Budworm outbreaks cost the forest industry billions of dollars, and of course the ecological impact is enormous (but poorly studied). One piece of that ecological impact might be changes in soil carbon dynamics. Caterpillar feeding produces a rain of frass that should immediately boost soil carbon, but in the longer term defoliated forests will see sunlight penetrate the canopy and warm soils, increasing microbial respiration and depleting soil carbon. We’re testing this idea by comparing soil carbon between stands defoliated by budworm and similar stands protected from defoliation by aerial spraying of the biological insecticide Btk. I’ll let you know how it turns out.

**^There’s a whole literature on the evolution of cooperation, but lest I take you down a rabbithole, I’ll leave it at that rather general statement.

***^Or their equivalent, of course – whether you prefer a carbon tax, or cap-and-trade, or some other mechanism that makes emissions more expensive doesn’t matter as much as doing something.

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One thought on “Tree trunks, game theory, and the invisible hand

  1. Pavel Dodonov

    In all my years collectings leaves with a pole pruner (which we call simply “podão”, or “big pruner”) and measuring tree height with an extendable measuring pole I’ve never had thoughts like this. Cool 🙂

    Liked by 1 person

    Reply

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