One of the most interesting aspects of environmental economics is the complexity of the tradeoffs involved. In most political questions, the issues are more black-and-white than grey; you seldom encounter highly-nuanced, intellectually even-handed discussions of issues such as Iraq, torture, abortion, and domestic spying. But with environmental issues, trade-offs abound. For example, we now have broad agreement that our dependence upon fossil fuels must be reduced. Yet, one of our good means of doing so, nuclear power, raises issues of its own. So we discuss, debate, and never seem able to come to a settled conclusion.
Monday, February 2, 2009
By Chris Crawford
I'd like to offer a micro-version of this problem: fire safety versus carbon sequestration. I am steward to 40 acres of forest land. The land has been much abused in the past; logging goes back at least a hundred years, and it has been seriously logged at least twice in the last twenty years. Fortunately, in neither case was the land clearcut; the owners left behind a goodly number of trees. In some cases this was only because the trees in question were unmarketable. Ponderosa Pines are subject to a process by which the trunk divides in twain twenty or thirty feet up; such trees, called schoolmarms, are unusable. We have a nice collection of schoolmarms on our land; they're the only big trees remaining. Some Douglas Firs undergo a related process that makes their trunks uneven; this also saves them from the chainsaw, and again, we have a nice collection of such trees. I've also planted thousands (I do not exaggerate) of seedlings, mostly Ponderosa Pine, but also some Douglas Fir. They're slowly growing in the areas denuded in times past.
But my problem concerns the handling of excess wood. There's lots of this. Twenty years ago an owner had horses, who chewed the bark on any oak tree less than eight inches in diameter. In many cases, the horses ringed the oak, killing it. In some cases, the horse couldn't get all the way around the tree, and a portion of the cambium was preserved, permitting the tree to survive and now, to recover. But these trees have their growth curtailed by the loss of cambium, and will always be structurally weak due to the exposed heartwood. In any case, I have at least a hundred dead oak trees on the land. It is a testament to the strength of oak that only about ten or twenty have fallen; the others are still standing 15 or 20 years after their deaths.
There are also plenty of dead firs. We had a bad drought about eight years ago. The firs started dying then, and the dying continued for about four years -- in the life of trees, everything happens slowly. Most of these trees were just a little too small to harvest during the logging 15 to 20 years ago, then grew to become the next generation of big trees, but died before that could happen. Hence we have a shortage of large trees on the land.
The Doug Firs don't remain standing as long as the oaks. Their root systems are shallow and their soft wood rots quickly. Every year about a dozen dead trees come down. I generate even more deadwood by my thinning efforts, and I also clear out the lower dead branches on the softwoods. All of this generates maybe 20 tons of dead wood every year.
If I want to do my bit for global warming, I should just leave all that deadwood in place. It sequesters carbon, keeping it bound up in the wood for decades. Eventually it will return to the atmosphere, but I can delay that process in a number of ways. If I leave the tree standing, it will last the longest, because it will remain dry. If it falls to the ground, then the soil moisture will accelerate its decay. Once a tree is on the ground, I could drag it off, cut it up, and burn it. And there's plenty of slash -- the piles of dead branches and small trees that I build when I cut up dead trees or thin sections.
But there's another factor to consider: fire safety. If a forest fire swings through this area, it could do enormous damage to the whole forest, as well as my house. Fire safety demands a number of practices:
1. Clear out all the thickets, pile everything into slash piles, and burn the slash piles in the winter.
2. Cut down all dead trees and burn the wood as firewood.
3. Thin the forest into something more like an open woodland rather then a dense forest.
But all three of these practices conflict with goal of carbon sequestration. If I want to sequester carbon, I should leave the dead trees standing so that they'll hold the carbon as long as possible. Moreover, slash piles provide cover for small animals; burning a slash pile kills its resident population. Thickets provide cover for deer; dense brush is necessary for small birds.
The trade-offs, as you can see, are almost impossible to balance. I have nevertheless struck a balance of sorts:
1. I leave dead oak untouched. Whether it's standing or fallen, it's best to just leave it in place. Why? Because it holds the maximum amount of carbon (it's dense); it holds onto that carbon longer (because it rots very slowly); and it poses the least fire danger (because it also burns slowly).
2. I haul off about half of the softwood for firewood. The firewood heats my house (I have a fireplace insert whose blowers I have augmented with boosters), so there's some overall benefit from burning the firewood. I leave the down wood in place where it wouldn't contribute much to the temperature of a fire or where the soil needs some more nutrients.
3. I throw some of the slash into the creek bed. This slows water flow in the creek, reducing erosion. The creek is too deep in some places; the slash will help fix this. Also, the slash in the creek will rot faster because of the increased moisture, putting more nutrients into the water and supporting (I think) a larger insect population, which in turn will provide a larger base to the food chain.
4. I just can't bring myself to burn the slash piles, even though in a fire, slash piles are very bad news. The fire penetrates the interstices of the slash pile and burns very hot, throwing out large numbers of hot sparks that advance the fire quickly. You don't fight forest fires by putting them out; instead, you keep them cool so that they affect only the ground cover and move slowly. Slash piles burn hot. My hope is that the slash piles will slowly compact, collect loess, and solidify enough before a fire comes through to make them less dangerous. After all, forest fires are rare; the last one to come through my valley was in the 1930s.
Those are my own trade-offs. But I'll never be sure that I've hit the right balance. If a fire hits sooner rather than later, the land will burn hotter and I'll end up losing more forest and maybe even the house -- and the larger fire will dump even more carbon into the atmosphere than would have been dumped had I burned the slash piles now. It's all a calculated risk.