PLANTATIONS: FIRE BOMBS IN THE FOREST

by Timothy Ingalsbee, Ph.D.

On the 1991 Warner Creek Fire, 28 existing plantations burned intensely causing complete mortality of the young reprod, and high-to-complete mortality of adjacent old-growth stands. In several of these units, the trees literally vaporized and barely any evidence of stems remains. The term catastrophic fire is appropriate for plantations because the effects of wildfire following timber extraction resulted in near total elimination of biomass, with no biological legacy or internal seed source left to reforest these stands. What is significant about the fire behavior and fire effects of these plantations is that these were the places where the ultimate in fuels reduction (clearcutting and slash-burning) has already occurred. Instead of reducing the intensity of the fire, the clearcut-plantations whipped up extreme fire behavior that resulted in catastrophic fire effects.

The removal of large (commercial lumber grade ) fuels and their replacement with fine and small fuels causes hot, fast-moving fires that defy the ability of firefighters to contain and control them. Indeed, on the Warner Creek Fire the Forest Service had to evacuate an entire division of firefighters when the fire encroached upon a zone of several plantations located on steep, south-facing slopes. When the wildfire entered these plantations, the blaze blew-up into a firestorm that hurled a tsunami of flame over the north side of Bunchgrass Ridge. Over 3,000 acres burned intensely on the day! This fire-killed old-growth bordering these plantations are now the prime salvage units desired by the Forest Service and timber industry.

Plantations burn with high intensity and rapid rate of spread because of their chemical and structural characteristics. Although old-growth Douglas-firs have evolved adaptations such as thick bark and high branches that enable them to survive most fires, young Douglas-firs do not have these advantages. The chemistry of Douglas-fir needles make them highly combustible; thus, plantations composed of densely stocked even-aged trees with their canopies intermixed and branches close to the ground are prone to extreme fire behavior. Additionally, old-growth stands have sufficient structural diversity (canopy closure and downed logs) to create microclimatic effects that tend to inhibit hot burns. The shade from the overstory reduces temperature and increases relative humidity and moisture of ground fuels. Likewise, large downed logs provide windbreaks from surface winds and often store huge amounts of water that takes heat energy out of fire. In plantations, however, the lack of structural diversity results in more exposure to sun and wind, resulting in more heat and oxygen to whip up intense fire behavior.

Firefighters almost never enter plantations to dig firelines (bulldozers are the exception to this rule). The high heat intensity and flame lengths, the rapid rate of spread, and the lack of mobility for ground crews to move through dense young stands make plantations extremely unsafe for fireline construction. In my years of firefighting, I have witnessed the most extreme fire behavior, including fire whirls and exploding gas balls, inside plantations.

Additionally, Forest Service policies mandate that suppression forces save the investments first (i.e. the plantations which cost the agency money to plant). Hence, on the Warner Creek Fire as on most wildfire suppression incidents in the Managed Forest, the agency used bulldozers and driptorches to cut and burnout fireline in 200 year old stands of native forest in order to save their 10 and 20 year old plantations. If they had simply plowed under these plantations they could have replanted and had the same thing in 20 years; however, the public will now have to wait 200 years or more to see old-growth in this area.

Plantations are not the place to fight fires, nor are they the place to salvage log (duh!). However, due to the extreme fire behavior of plantations, they can cause increased mortality of adjacent old growth. Ladder fuels need not be present for the intense heat in the convection column of burning plantations to kill and sometimes torch the canopies of adjacent old-growth Douglas-firs (mortality results from 90 seconds or more of 140 degrees Fahrenheit). This was how the big blow-up unfolded on the Warner Creek Fire: the intense heat of the convection columns from the burning plantations, compounded by the unobstructed surface winds blowing upslope across these clearcut areas, set ablaze the canopies of adjacent 250 foot tall old-growth trees, creating a canopy fire where in normally and naturally should not happened. Thus, by no mere coincidence, nearly all salvage logging units on the (now defunct) Warner South salvage sale bordered plantations because this is where the high mortality of native old-growth stands occurred.

The agency is perpetuating a lie when it claims that fuel reduction for fire protection constitutes fire recovery of a burned landscape. The relationship between forest fuels and fire behavior is a qualitative, not quantitative one. Thus, although the agency may be reducing the gross amount of fuel for potential future fires when it salvage logs, the net effect of eliminating structural diversity and extracting large fuels is that it creates the kind of fuel profile that is most susceptible to intense, severe, catastrophic fire. Like a jigsaw puzzle in reverse, the agency continues to pluck adjacent pieces of the forest out when it salvage logs old-growth adjacent to burned plantations. And with each new wildfire, this process of salvage clearcutting and monocrop replanting functions to prime the pump for future catastrophic wildfires.