California: Too often thinning treatments tend to increase fire hazards

A recent report by the Forest Service in California is worth reading
because it describes the abject failure of fuel treatments conducted
on the Tahoe National Forest when the American River Canyon Complex
Fires burned through the treatments earlier this year. Only one of
the many thinning treatments mitigated fire mortality of the stands
where the agency required whole-tree yarding and didn’t leave slash
piles or other fine fuels from the thinning. Both mastication and
slash piles after thinning actually helped carry the fire through
thinned stands and increased mortality (and severity).

Also
interesting is that green shrubs in the understory helped reduce fire
severity in this early season burn because of their moisture content.
The following description of the report comes from Sierra Forest
Legacy’s web site: A study of fire severity effects in the region of
the American River Complex Fire on the Tahoe National Forest has just
been released by Forest Service Regional Ecologist Hugh Safford. The
lightning ignited fire burned approximately 20,000 acres from June 21
through August 1, 2008. The study was undertaken to evaluate the
effectiveness of previous stand treatments designed to reduce fire
severity. The report confirmed the great importance of treating
surface fuels with prescribed fire in order to reduce future fire
severity and spread. Thinning alone was not sufficient to prevent high
levels of mortality and fire spread. Stands which had been
mechanically thinned, and then treated with prescribed fire to reduce
the surface fuels, were significantly more resistant to severe fire
effects. The report confirms earlier research conducted by Scott
Stephens and Jason Moghaddas (2005) at Blodgett State Forest which
predicted these precise outcomes. Grapple piles, or piles of logging
slash that are supposed to be burned after logging but which
frequently are left unburned, also contributed to high stand
mortality. The report provides additional confirmation that fuels
treatments must be considered a part of every timber harvest removal,
regardless of the scale or objective. These treatments must be
conducted before any forest project is considered complete. In some
instances, the use of mechanical thinning alone increased fire
mortality. In addition, plantations which contained live, dense green
shrubs resisted fire significantly better than plantations that had
been mechanically masticated. Safford notes, “In a number of cases,
the persistence of dry surface fuels in the masticated units appears
to have abetted rather than resisted fire.” Such surface fuels can
persist in the Sierra Nevada’s dry forests for decades.
http://www.sierraforestlegacy.org/index.php

Posted via email from Deane’s posterous