ARCHIE CREEK REVISITED: Lessons From Pacific Northwest Megafires?

Published December 8th, 2022 in Restoration

Ken Carloni, Ph.D.

Two years ago, I wrote an article in the 100 Valleys on the Archie Creek Fire and its implications for future forest management¹. Recently, I was alerted to a video² produced by The Nature Conservancy (TNC) on the effects of the 2021 Bootleg Fire on forest land that they manage east of Chiloquin, OR in the Sycan Marsh area. The video highlights the behavior of that fire in areas that TNC had thinned and burned compared to untreated areas. I had known that the Bootleg burned through areas that had been treated for fire resiliency by both the TNC and the US Forest Service in a number of ways, and have anxiously awaited the results ever since. The video prompted me to look more closely at these outcomes, and to revisit the Archie Creek Fire to see if they might be applicable on this side of the Cascades. Although the TNC video indicates that their thinning and burning efforts were highly effective at least in some areas, the story is much more complicated.

Data analyzed in a ground-breaking study³ of the 2013 Douglas Complex Fire in southern Douglas County showed that the most important factors influencing fire severity are extreme weather followed by forest management practices and to a lesser extent topography. Subsequent studies of the 2020 Cascade fires⁴ (including Archie Creek) and the 2021 Bootleg Fire⁵ reinforced these findings, and all concluded that weather is the strongest driver of fire severity.

But when wind speed, temperature, and humidity were closer to average, all of these studies found that, forest ownership patterns had the strongest impact on fire severity. Private industrial forest lands are dominated by even-aged plantations with a densely packed, uniform fuel structure that has little resistance to high-mortality crown fires. Older primary forests hold more moisture, have trees with uneven heights and branching patterns that discourage crown fires, and have large trees with thick bark that protect them from ground fires. These older forests exist almost entirely on public lands.

The effects of management regimes on fire severity can also be seen at larger scales on lands with differing levels of forest protection. A recent study⁶ that analyzed data from 23.5 million acres of western pine and mixed-conifer forest found that burn severity tended to be lower in areas with more ecological protections (less intensive management), after accounting for topographic and climatic conditions.

Data from the Archie Creek Fire also indicate that after weather, forest management is the primary driver of fire severity. Under extreme wind conditions in the first 24 hours of the fire, ~95,000 ac. of the 131,000 total acres burned, and severity on public land was only slightly lower than on private land (75.3% and 80.7% respectively). However, on subsequent days when windspeeds decreased to more typical conditions, fire severity on less intensively managed public land dropped significantly compared to private industrial lands (35.3% vs 47.0%). This effect was even more dramatic on the Holiday Farm Fire just to the north, with public lands experiencing only half of the mortality of private lands (23.9% vs 46.3%) under more average wind speeds.

While there is photographic evidence that thinning and under-burning on TNC land in the Bootleg Fire decreased mortality in at least some cases, another analysis by Forest Watch⁷ suggests that thinning and other vegetation treatments did little to slow the spread of the Bootleg Fire during extreme weather. Given the steadfast inability (or flat-out refusal) of a large portion of the planet’s population to come to grips with the climate crisis, we can expect more extremely hot, dry and windy conditions to coincide with fire ignitions well into the future. Many analysts believe that we are just wasting our money on thinning projects that can fail spectacularly⁸ as they did during the Camp Fire that destroyed the town of Paradise, CA. Rather than spending public funds in the backcountry, they instead argue that those funds are better spent on more fire-resistant building design and more intensive fuels management in the Wildland-Urban Interface.

But extreme fire weather is still the exception rather than the rule, and TNC’s thinning work in the Sycan Marsh and other studies⁹ suggest that under mild to moderate weather conditions, thinning can be an effective tool to reduce fire severity risk, particularly when followed by prescribed fire.

Restoration ecologists (including me) are taking a more holistic approach to “active” forest management, thinning our forests in ways that mimic historic conditions while promoting biodiversity AND fire resilience. Although I strongly agree that concentrating our work around homes and infrastructure is the best way to spend fire resilience dollars, I am still an advocate for thinning in remote plantations (but not in primary forests) for two reasons.

First, proximity to highly flammable plantations puts our dwindling acres of precious old growth in greater jeopardy of being lost for centuries in high severity burns. Protecting these important reserves of carbon and genetic diversity is a challenge to which we must rise to give ancient forests a fighting chance to survive for the benefit of future generations.

Second, the pattern of forest thinning can serve other ecological goals in between fires. Typically, forests are “grid-thinned” creating a uniform structure that is less resistant to wildfires than stands thinned with “clumps and skips”. This patchy structural configuration more closely emulates the chaotic patterns of historic wildfires, adding structural diversity to the landscape that promotes biotic diversity in return. “Thinning from below” (taking the smallest trees and leaving the largest), removes the “ladder fuels” that can carry a fire from the forest floor to the canopy, and leaves the largest, most fire-resistant trees on site. And creating small, scattered openings creates more habitats to support a wider variety of understory plants and wildlife.

The takeaway here is that wildfire is complicated — weather, management, and topography all have significant impacts on fire severity, and they all interact with each other in often highly unpredictable ways. It is clear that under extreme fire conditions, thinning treatments do little to decrease fire severity. However, thinning plantations in ecologically appropriate patterns to minimize the loss of adjacent old growth resources under most conditions is an effort worth making to protect our descendants’ natural heritage.

References:

Share on Facebook

Restoration

ARCHIE CREEK REVISITED: Lessons From Pacific Northwest Megafires?

Enjoy this blog? Please spread the word :)