I’ve come to believe that quite a lot of our ideas about how the world should be effervesce from a sort of cosmic gumbo of influences: media, our friends, world events, temperament, a case of heartburn. We then buttress these ideas with enough facts and logic to grant our minds some degree of repose. While I think the dynamic plays out broadly, it is certainly true in the case of the natural world, where we often feel it necessary to justify our preferences with gestures in the direction of what things would be like absent human interference.
Such was my thinking as I perused a fascinating article about brook trout in Vermont. Brook trout are native to North America, and there are widespread efforts to protect them from competition and to increase their numbers. To this end, in certain tributaries to trout streams, wildlife management officers have been sinking tangles of brush into the water.
The practice does a few things. It alters the current, making some areas faster and others slower, some shallow and warm, others deep and cool. It catches leaves, which provide food and habitat for the insects that brook trout feed on. By catching sediment and slowing floodwater, it keeps the broader stream ecosystem healthier.
The results have been remarkable. By giving the trout cover, shade, more food and more varied habitat, the snarls of brush have led to a huge increase in their population. In one sampled stream fish numbers and biomass tripled. It’s a wonderful example of a simple intervention leading to a big change.
But I’m also interested in the justification for installing these breakwaters in the first place. The biologist quoted in the article says that the old growth forest that once covered New England would have routinely led to similar tangles of branches due to trees falling into streams.
This may well be true, though with the current level of tree cover in Vermont I’m not positive it’s the case. Even if it is, the old growth forest of a few hundred years ago was the result of human management by the native peoples of the area. Further back, roughly 10,000 years ago, the whole area was covered by glaciers. When these retreated the streams that formed would have passed through a landscape void of trees. In the centuries between the ecosystem was perpetually shaped not just by shifting populations of animals and plants, but also by humans. (Here’s a good, brief summary if you’re interested.)
My point is not that we shouldn’t try to understand how ecosystems functioned in the past, but rather that we should understand that they have always been shifting, and that humans have long played a role in giving them whatever shape they have in a particular moment. Picking an arbitrary point in the past and trying to recreate it in the present is a recipe for frustration.
To take the example I’ve been discussing, I think we should be exploring ways to increase brook trout population because we like brook trout, more biodiversity is generally a good thing, and streams that are less prone to flooding and erosion cause fewer problems for everybody. If tomorrow a biologist released a groundbreaking study that somehow proved brook trout populations were actually quite low in the year 1500, it wouldn’t change my opinion of how streams should be managed today.
I wonder if part of the appeal of looking backwards is that it avoids having to think about why we're making the choices we are. A more difficult approach would be to ask how we can best manage a particular resource right now, to clearly articulate a goal for that management approach, to acknowledge tradeoffs known and unknown, and then decide whether or not to pursue it with appropriate humility. As I say, hard, but I think better in the long term. It might even be a useful way to think about problems thornier then helping trout stay cool.