Environmental Assessment

AFFECTED ENVIRONMENT & ENVIRONMENTAL CONSEQUENCES CHAPTER 3
Silvicultural/Vegetation Effects (thinning) related to Fire/Fuels
These proposed treatment (thinning) will reduce the risk and potential of a crown fire by increasing the
distance between residual trees. Stands under both action alternatives would be thinned from below. The
distance from the ground to the base of the live crown would increase and average from 20 to 30 feet,
depending on residual tree size (Silviculture Report, page 20). By increasing the height to the live crown,
the thinning also breaks up vertical fuel continuity (ladder fuels) and reduces the risk of a surface fire
climbing into the canopy. Thinning from below would also increase the distance between tree crowns
thereby reducing the risk of a crown fire by requiring higher wind speeds to allow the fire to climb into
the canopy and to spread the fire between trees. Mortality rates would be expected to decline and the
number of mature and old growth aged trees lost to fire would decline.
Thinning through the application of prescribed fire and mowing also serves to reduce the quantity and
distribution of understory shrub vegetation. It also serves to reduce the quantity and distribution of needle
cast captured by understory vegetation. This also helps to reduce ladder fuels and the risk and potential
for a crown fire developing from a ground fire.
Thinning in the overstory tree component would also increase light levels and nutrient availability to
understory vegetation. When combined with thinning in understory vegetation, which also reduces
understory densities, thinning also increases the amount of space available for the initiation of new
vegetation. This increase in understory vegetation would begin the process to restore understory ladder
fuel levels and distribution to pretreatment levels in the five (5) to 15 years following treatment.
In the short-term, 3 to 5 years or so, thinning also reduces competition and increases the availability of
nutrients, space, and light for residual vegetation. That vegetation responds with increased growth. In the
long-term, this increase in resources also provides opportunities for new vegetation to become
established. Both result in new increases in the amount and distribution of both horizontal and vertical
(ladder) fuels. Such ingrowth, plus the expansion of residual tree crowns into the newly opened space,
would be expected to require retreatment within one to two decades depending upon post-harvest spacing
and growth to return these stands to a low fire behavior potential level.
The primary differences between the two alternatives are: 1) there would be fewer entries to accomplish
the objectives under Alternative 3; and 2) pretreatment activities prescribed under Alternative 2 would
eliminate all trees four (4) inches dbh and smaller whereas Alternative 3 would pretreat fewer acres
through all diameter classes and retain individuals trees four inches dbh and smaller.
All Alternatives:
The risk and threat of a wildfire threatening improvements would remain high across the planning area
under Alternative 1. No fuel reduction or vegetation treatments would be initiated that would reduce fuel
loading or increase the probability of suppressing a fire before reaching major improvements or facilities
such as the observatory, electronic sites, or the BPA substation and transmission lines. Flame lengths and
rates of spread would remain high, increasing the difficulty in controlling the fire. Improvements
associated with other resource uses including OHV facilities, other recreation sites, and grazing
improvements such as fences, water troughs, and analysis plots would also remain at risk.
Both action alternatives would reduce the risk of a wildfire threatening improvements at Pine Mountain
(specifically the observatory and electronic sites). This would be accomplished by breaking up fuel
continuities, reducing fuel loadings, and reducing the risk of spot fires. Control using hand crews would
be easier due to decreased flame lengths and rates of spread. Under Alternative 2, units F03, F08, F19,
and F25-27 would reduce the risk of a wildfire spreading from the Pothole flats area on the southwest side
of Pine Mountain up the slopes towards the observatory and the electronic site just west of the
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