PORTLAND, OR. April 9, 2007. A new study
on the effects of timber harvest following wildfire shows that
the potential for a recently burned forest to reburn can be high
with or without logging. Recently published in the journal, Forest
Ecology and Management, the study demonstrates that the likelihood
of a severe reburn is affected by the timing – not just the
amount – of fuel accumulation after fire.
The study examines
fuel accumulation with and without logging after a large wildfire
in the Blue Mountains of northeast Oregon.
Three treatments were examined: commercial logging that removed
only dead trees with value for wood products, commercial logging
plus thinning that removed all dead trees larger than 4 inches
in diameter, and unlogged sites.
The year after logging (3 years
after the fire), sites that were logged and thinned had four times
more fine fuels on the ground,
as a result of logging residue, compared to unlogged sites. Those
same sites also had fewer snags– which provide habitat for
woodpeckers, owls, and other animals that nest in tree cavities – and
contribute to large woody debris on the ground. However, logging
activity caused no change in the litter or duff, the upper soil
organic layers that also affect how a fire burns. The study was
led by James McIver of Oregon State University and Roger Ottmar
of the Pacific Northwest Research Station, U.S. Forest Service.
investigators used a computer model to project how fuels and fire
hazard would change over time. “Long-term research and
monitoring are not always possible,” says McIver. “Although
we would rather have the long-term data, using a model allows us
to estimate some of the future ecological effects.”
The computer simulation showed that the difference in surface
fuels between logged and unlogged units would persist for about
15 years. The simulation also showed that if a fire did start during
this time, it would likely kill most young trees as the fire carried
through either logged or unlogged stands, even though the logged
stands had higher slash fuels. This is because other components
of the fuel bed (grasses and shrubs) would contribute significantly
to fire conditions, whether sites were initially logged or not.
“The exact nature of fuel accumulation over time is the
key to understanding fire hazard,” explains Ottmar. “Each
forest, each fire, and each logging operation affects fuels differently,
and variation exists within any forest stand. It is also important
to consider the whole fuel bed when thinking about fire hazard
in the future.”
Model projections indicated that large fuels will increase over
time in the unlogged forests as dead trees fall over, with up to
three times greater fuel accumulation as compared to a wildfire
area that has been logged. Although it would seem that any extra
fuel would be a cause for concern, these large fuels do not carry
fire well on the surface, and so do not tend to create conditions
for crown fires. Rather, they will tend to cause long periods of
heating on the ground.
“Wood can be fuel in the short term or the long term,” says
McIver, “but that’s only part of the story. Wood is
also wildlife habitat, and wood provides nutrients to the soil.
Fire, ecological factors, and management objectives are all important.
Our data show that there are no simple answers.”
To read the study, “Fuel mass and stand structure after
post-fire logging of a
severely burned ponderosa pine forest in northeastern Oregon,” visit
click on postfire logging paper published.