11/15/12 - unintended consequences and forest fires

In today's encore selection - unintended consequences and forest fires:

"The U.S. Forest Service in the first decade of the 1900s adopted a policy of fire suppression (attempting to put out forest fires) for the obvious reasons that it didn't want valuable timber to go up in smoke, nor people's homes and lives to be threatened. The Forest Service's announced goal became, 'Put out every forest fire by 10:00 A.M. on the morning after the day when it is first reported.' Firefighters became much more successful at achieving that goal after World War II, thanks to the availability of firefighting planes, an expanded road system for sending in fire trucks, and improved firefighting technology. For a few decades after World War II, the annual acreage burnt decreased by 80 percent.

"That happy situation began to change in the 1980s, due to the increasing frequency of large forest fires that were essentially impossible to extinguish unless rain and low winds combined to help. People began to realize that the U.S. federal government's fire suppression policy was contributing to those big fires, and that natural fires caused by lightning had previously played an important role in maintaining forest structure. ... Take the [Montana's] Bitterroot low-altitude Ponderosa Pine forest as an example, historical records, plus counts of annual tree rings and datable fire scars on tree stumps, demonstrated that a Ponderosa Pine forest experiences a lightning-lit fire about once a decade under natural conditions (i.e., before fire suppression began around 1910 and became effective after 1945). The mature Ponderosa trees have bark two inches thick and are relatively resistant to fire, which instead burns out the understory of fire-sensitive Douglas Fir seedlings that have grown up since the last fire. But after only a decade's growth until the next fire, those seedlings are still too low for fire to spread from them into the crowns. Hence the fire remains confined to the ground and understory. As a result, many natural Ponderosa Pine forests have a park-like appearance, with low fuel loads, big trees well spaced apart, and a relatively clear understory.

"Of course, though, loggers concentrated on removing those big, old, valuable, fire-resistant Ponderosa Pines, while fire suppression for decades let the understory fill up with Douglas Fir saplings that would in turn become valuable when full-grown. Tree densities increased from 30 to 200 trees per acre, the forest's fuel load increased by a factor of 6, and Congress repeatedly failed to appropriate money to thin out the saplings. Another human-related factor, sheep grazing in national forests, may also have played a major role by reducing understory grasses that would otherwise have fueled frequent low-intensity fires. When a fire finally does start in a sapling-choked forest, whether due to lightning or human carelessness or (regrettably often) intentional arson, the dense tall saplings may become a ladder that allows the fire to jump into the crowns. The outcome is sometimes an unstoppable inferno in which flames shoot 400 feet into the air, leap from crown to crown across wide gaps, reach temperatures of 2,000 degrees Fahrenheit, kill the tree seed bank in the soil, and may be followed by mudslides and mass erosion.

"Foresters now identify the biggest problem in managing western forests is what to do with those increased fuel loads that built up during the previous half-century of effective fire suppression. In the wetter eastern U.S., dead trees rot away more quickly than in the drier West, where more dead trees persist like giant matchsticks. In an ideal world, the Forest Service would manage and restore the forests, thin them out, and remove the dense understory by cutting or by controlled small fires. But that would cost over a thousand dollars per acre for the one hundred million acres of western U.S. forests, or a total of about $100 billion. No politician or voter wants to spend that kind of money. Even if the cost were lower, much of the public would be suspicious of such a proposal as just an excuse for resuming logging of their beautiful forest. Instead of a regular program of expenditures for maintaining our western forests in a less fire-susceptible condition, the federal government tolerates flammable forests and is forced to spend money unpredictably whenever a firefighting emergency arises: e.g., about $1.6 billion to fight the summer 2000 forest fires that burned 10,000 square miles."


Jared Diamond


Collapse: How Societies Choose to Fail Or Succeed


Penguin Books


Copyright 2005 by Jared Diamond


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