Commentary

Unnatural History

Hurricane Katrina — a very big storm by any measure — has now been called the “largest ecological disaster in U.S. history,” according to the Christian Science Monitor, because it “killed or damaged about 320 million trees.” Moreover, Katrina was a double ecological whammy, as the downed trees will eventually rot or burn, releasing another increment (probably too small to detect) of dreaded carbon dioxide, the main global warming gas. The Monitor’s report was based upon an analysis of satellite imagery conducted by scientists at the University of New Hampshire.

Wait a minute. Hurricanes have been a fact of life for the forests of southeastern North America ever since there were forests, and that’s a pretty long time.

The natural vegetation of the coastal southeast consists largely of a mixture of Pine and Oak species. That’s not what it is today, because today’s vegetation isn’t natural. Rather, it’s virtually all a commercial mix of softwoods designed to grow fast and tall, so the trees can quickly be sawed into houses. Today’s forest probably maintains a higher vertical profile than the one that was here before, and it’s also largely protected from fire, but not from hurricanes.

Back before us, believe it or not, weather was pretty much the same as it is now. Consider the very severe drought currently plaguing the Deep South. Remember those forest fires in Georgia late last summer? The only reason they didn’t burn down most of the state’s forests was that they were unnaturally extinguished.

It’s fair to say that the integrated intensity of the southeastern drought may be a one-in-fifty year occurrence. That would mean, in a “natural” world (i.e., one without human sprawl) a southeastern forest would go about fifty years before combusting.

Or, perhaps, taken down by a hurricane. Pines and oaks have been around about 100 million years. Hurricanes have been around longer.

Here’s the cool part: the present era. Ninety-five percent of the last 100 million years were warmer than now. It’s only about 5 million years or so ago that we began to slip into the current ice-age climate (from which carbon dioxide may mercifully extricate us, some say).

Weather and climate are now assumed to be driving the world into ecological chaos. It seems reasonable that, say, 30 years from now, something else will be to blame. ”

Now, just for fun, let’s assume that Katrina was a product of global warming. Forget that no scientist will stand up and point the causative finger. But, if it was, Katrina was therefore typical of many hurricanes of the last 100 million years. In other words, the natural southern forest evolved in a world studded with Katrinas.

Part of the modern climate mythology is the assumption that every significant climate burp, such as the big El Nino of 1998, or the big hurricane season of 2005 is portentous of ecological disaster. Hardly. In fact, if today’s species were not adapted to these extremes, they simply wouldn’t be here.

It’s almost too bad that we don’t have the “natural” forest of southeastern North America anymore. I’ll bet, if we did, that some ecological researcher would have discovered indeed that such a forest in fact requires hurricanes, just as the flowering plants of the desert southwest require El Nino rains for germination and subsequent reproduction.

There once was a concept of “potential natural vegetation” of the United States, which was thought to be what would eventually appear in the absence of human management. The modern view of forest dynamics is somewhat different, but, nonetheless, the “natural” distribution of the oak-pine forest pretty much corresponds to the inland reach of the strongest hurricanes.

OK, that was my original Ph.D. topic proposal, back in a 1971 paper at the University of Chicago. It was laughed at, because, at the time, ecologists didn’t think weather or climate were very important modulators of ecosystem behavior. Four years later, the surface temperature of the planet began to rise. About a third of a century later, a hurricane was blamed for the largest ecological disaster in our history.

Now it’s the other way around. Weather and climate are now assumed to be driving the world into ecological chaos. It seems reasonable that, say, 30 years from now, something else will be to blame.

Finally, whenever a hurricane (or a fire) takes down a forest, it’s not replaced by anything but another forest. That vegetation will absorb some of the carbon dioxide that Katrina’s trees left behind. It will eventually look a lot like the one that got blown down, only to await the sawmill, or the next big hurricane.