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FEB. 7, 2014

Life in the Boundary Layer

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Two of the books I’m reading right now are colliding a bit. Lately, I’ve become interested in identifying some local bryophytes – mostly mosses – after a new field guide was published last year. I just picked up Gathering Moss by Robin Wall Kimmerer, a John Burroughs Medal Award winner to help me out. The second book is How to Read Literature Like a Professor by Thomas C. Foster. I’m so fascinated with the craft of writing fiction and, at the same time, so ignorant. I was the kid that complained “Oh come on, the author didn’t write all that symbolism in there.” Turns out they did. My apologies, Miss Schmidt.

Early on, Robin Kimmerer mentions the boundary layer as she discusses moss habitats. This phenomena of edges and interfaces shows up a lot in science and literature. It is analogous to the way the Gulf Stream spins off eddies on the Atlantic coast as the edges of that northern current slow down due to contact with the shallow littoral zone. It also reminds me of the ecotone boundary between habitats – often a more species-rich area than either of the habitats. In fact, some of her graduate studies looked at what’s called the Intermediate Disturbance Hypothesis, the observation that diversity is often highest in the areas between the extremes. One of her examples is a moss community on a riverside cliff in Wisconsin. A few dry-adapted species live high up, a couple of flood-adapted species live close to the water, but many more may live in the zone between. Where the disturbance is frequent or harshest, in this case either often dry or often wet, only a few highly specialized species survive.

But back to the boundary layer. I’ve been studying the granitic outcrop habitat of Cedar Rock in DuPont State Park just down the road. This is a 250 million-year-old crystallized magma bubble called a pluton – a big, rounded rock hill. It’s a difficult environment for plants; there is little soil or water and lots of exposure. It’s baked in the summer sun and scoured by the wind in winter. In the case of the Cedar Rock bryophytes, success is mostly a matter of getting out of the wind. When air travels over any surface, the flow is disrupted by contact with that surface. Even the tiniest patch of moss increases that disruption and creates a boundary layer of still air maybe only a few centimeters high. This has at least four effects: it traps and warms air at the substrate surface; it lowers evaporation, creating a humid zone; and it raises the availability of carbon dioxide by trapping the gases released by the decomposition of rotting organics. Well, let’s see… mosses need light, warmth, carbon dioxide, and water. Apparently their very presence generates their own microhabitat – they are not hanging on for dear life in a tough environment as it appears. On a sunny day they finish their shopping early and snack and nap away the afternoon. They’ve been doing this on the planet for 350 million years now.

Mostly, this surprises and pleases me because it seems so contrary to our experience of extracting and sometimes bludgeoning our resources from the environment at such high costs. Imagine that simply lounging in the sun brought you food and water and oxygen. It sure begs the question why mosses and not ants or red-tailed hawks or lizards or us? Well, of course, we aren’t photosynthetic producers on the trophic pyramid and must rely on eating those who are, or their predators, called herbivores. But there are a few photosynthesizing animals in our ancestry, like the protist Euglena. Certainly that would have been the evolutionary motherlode. A missed opportunity, to be sure.

Oh yes, the second book. Symbolism in literature. Hmm… I thought there was a tie-in here, but I’m no English major. I’ll get back to you on that. I will say that I have been thinking of our school as a place where we create a boundary layer. Much of it is very intentional and defines The Outdoor Academy structure. But like natural selection in bryophytes, much of our day-to-day experience here also reveals a surprise secondary effect created by a boundary layer that gives us the security to explore new adaptations and niches that will reduce competition and maximize peaceful coexistence and production. We call this effect community.

Ted Wesemann