5 May 2011, 8:39am
Forestry education
by admin

Fire Cycle Regularity

I made a wrong statement the other day, and I wish to correct myself. What I said was, “there are not clockwork deterministic cycles in nature.” Of course, there are.

One example is the Ice Ages. Over the last 1.9 million years there have been 18 Ice Ages (or glaciations) each lasting ~105,000 years and 18 interglacials (like the present Holocene) each lasting ~10,000 years. The glaciations come like clockwork at long intervals which happen to correlate with perturbations in the Earth’s orbit known as Milankovitch Cycles.

Another example: human females of reproductive age have menstrual cycles of 28 to 29 days, which correlate with lunar cycles (new moon-full moon-new moon).

Not everything in nature is subject to deterministic clockwork cycles, though. The topic I was propounding on the other day was fire cycles.

Forests can burn and do burn, but not necessarily at regular intervals. Not at “natural” regular intervals, that is. Forests are not subject to pyro-menstrual cycles. There are no celestial pendulums that govern forest fires.

Forests do accumulate fuels. As fuels build-up, the likelihood of a fire increases. Eventually a fire will happen, but they do not happen at regular intervals — unless people do the fire lighting!

People are not clockwork automatons, but we sure do act like it sometimes. Witness traffic jams caused by commuters who all commute at the same time. Or take the Olympics, or elections, or leap years, or bicentennial fetes. Nothing in nature dictates those cycles; they are entirely anthropogenic.

Forest fires have been mostly anthropogenic (human set) for tens of thousands of years (perhaps for hundreds of thousands of years in Africa). Humans sometimes set fires accidentally, but most of the time there is purpose to our pyromania — humans set fires deliberately for reasons. Those reasons may or may not be rational or wise, but we have our reasons nonetheless.

Because we are human and tend to do our stuff on regular schedules, historical fire cycles do indeed display regularity. But that regularity is not something inherent to forests; it is something inherent to people.

Something else that is inherent to people is awe and wonder. We like to be thunderstruck (figuratively, not literally). We also like to blame external agents, particularly supernatural agents (God, Mother Nature, Gaia, space aliens, etc.) for whatever happens. Blaming God for everything stems from laziness of the mind, however, and is not scientific. When scientists blame God (or Mother Nature, Gaia, space aliens, etc.), they are not really doing science — they are in fact doing superstitious nonsense.

There is a tendency to be lazy that is well-established in the human genome. I have the lazy bug; so do you. Come on now, admit the truth (maybe later, when you have more energy, after your nap). Lazy thinking in particular is commonplace.

But science is no place for lazy thinking. Forest scientists who study fire cycles need to exercise their brains a little more rigorously. Take a good hard look at those fire scars. Think to yourself, what started those fires? If your answer (to yourself) is lightning, not people, then ask yourself what evidence you have one way or the other.

Because if the fire cycle you perceive is regular, that is evidence that people were responsible, Q.E.D.

5 May 2011, 10:29am
by Tim B.

Right On, Mike. I have a small section from a fire scarred pine (windthrown) on my desk; you may have seen this. This chunk of wood contains 5 fire scars, with an average interval of 11.5 years, (ranging from 9 to 13) between events. I pull this out when I sense someone I am talking to about fire history/ecology is unwilling to accept the premise that much of the past fire history is anthropogenic in origin. Curiously, these regular fire scars seldom convince any better that what I may be saying. Its curious that people can see this kind of regularity and ascribe it to cyclic or random natural events, even though these same people can look/think back on the fire events they have witnessed over a long career without seeing such a regular pattern.

Lazy thinking to be sure, but in a way more insidious than simple sloth or indolence; the resistance is not only in thinking about something, but being willing to closely consider (and maybe discard) previously held notions. This reminded me of a conversation I had with a good friend and very intelligent guy about Charles Mann’s book (1491, here). My friend had not read it so I gave him the synopsis and some of the most interesting supporting information, but it didn’t matter; my friend was not willing to accept that there were so many people here having such an impact on their world. When I questioned him about why he could not accept this hypothesis given all the supporting information, he replied “That’s not what I was taught”! Consider that when this guy was taught geology in high school, continental drift was a theory that most dismissed, yet my friend does now believe it to be true now. Yep, I guess too much thinking can just wear you out.



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