Thinning mature trees ups fire risk
By Chad Hanson - Sat, Aug 25, 2001
The Union Grass Valley/Nevada City, CA
In his recent column, Steve Eubanks, supervisor of the Tahoe National
Forest, states that commercial thinning of mature trees from 10-30
inches in diameter reduces the risk of wildfires, though he cites
no scientific authority to support this claim. He would be hard pressed
to do so, since the Forest Service's own science clearly takes the
For example, the recently released Sierra Nevada Forest Plan states
that reduction of forest canopy cover actually causes more severe
fires by increasing the velocity of "mid-flame winds." Further,
the Fire and Fuels section of the Sierra Plan acknowledges that "in
areas where the larger trees have been removed, stand replacing fires
are more likely to occur." This same section, for the purposes
of fire and fuels management, defines "large trees" as
those over 12 inches in diameter.
In a nutshell, commercial thinning reduces forest canopy cover,
eliminating the moist, cool, shaded conditions associated with mature
forests. The result is hotter, drier conditions on the forest floor
- a situation ripe for severe wildland fires. In addition, logging
leaves behind extremely flammable slash debris consisting of dry
twigs and branches.
The Forest Service's own National Fire Plan warns that the agency's
wildland fire policy should "not rely on commercial logging
or new road building to reduce fire risks" because "the
removal of large, merchantable trees from forests does not reduce
fire risk and may, in fact, increase such risk." The National
Fire Plan also finds that "logging and clearcutting can cause
rapid regeneration of shrubs and trees that can create highly flammable
fuel conditions within a few years of cutting."
Even the Forest Service's chief fire specialist, Denny Truesdale,
repeatedly stated in an Aug. 10, 2000 interview on the C-SPAN program "Washington
Journal" that the material that needs to be reduced to prevent
severe fires is undergrowth less than 3 or 4 inches in diameter -
not mature trees. In fact, the Forest Service's BEHAVE model, which
measures potential for fire spread, doesn't even consider material
larger than 3 inches in diameter.
Mr. Eubanks is correct that in some areas prescribed burning alone
cannot effectively prevent severe wildland fires. In some cases,
undergrowth comprised of saplings, shrubs and twigs should be manually
reduced prior to prescribed burns. In fact, dozens of such projects
are being implemented right now on Sierra Nevada national forests
through service contracts. None of them are being challenged by environmentalists.
Challenges occur only when the Forest Service removes mature trees
through commercial logging operations or through timber sales embedded
in service contracts. Such activities not only seriously degrade
habitat for imperiled forest species such as the California spotted
owl and Pacific fisher, but they also increase the incidence and
severity of wildland fires.
Finally, Mr. Eubanks states that he encourages commercial thinning
of mature trees on the Tahoe National Forest supposedly in order
to protect homes on adjacent private lands from fires. Yet the Forest
Service's own scientific expert on this issue, Jack Cohen, has published
recent studies which conclude that the only way to effectively protect
homes is to reduce the flammability of the home itself and its immediate
surroundings within at most 40 meters. The commercial thinning operations
on Sierra Nevada national forests, including the Tahoe, are typically
miles from the nearest home.
The Forest Service's credibility would be greatly enhanced if the
agency would simply admit that it continues to cut down mature trees
for their timber commodity value, and nothing more. If the commercial
logging program on national forests were ended, the agency would
be able to focus on real fire risk reduction efforts, rather than
continue to waste taxpayer money on timber sales that destroy habitat
and cause severe fires.
Chad Hanson is the executive director of the John Muir Project and
a national director of the Sierra Club.