The Missing (PNW) Fires

Abstract from a new paper in Ecosphere, “The missing fire: quantifying human exclusion of wildfire in Pacific Northwest forests, USA.” Full text is online, free:

Western U.S. wildfire area burned has increased dramatically over the last half‐century. How contemporary extent and severity of wildfires compare to the pre‐settlement patterns to which ecosystems are adapted is debated. We compared large wildfires in Pacific Northwest forests from 1984 to 2015 to modeled historic fire regimes. Despite late twentieth‐century increases in area burned, we show that Pacific Northwest forests have experienced an order of magnitude less fire over 32 yr than expected under historic fire regimes. Within fires that have burned, severity distributions are disconnected from historical references. From 1984 to 2015, 1.6 M ha burned; this is 13.3–18.9 M ha less than expected. Deficits were greatest in dry forest ecosystems adapted to frequent, low‐severity fire, where 7.2–10.3 M ha of low‐severity fire was missing, compared to a 0.2–1.1 M ha deficit of high‐severity fire. When these dry forests do burn, we observed that 36% burned with high‐severity compared to 6–9% historically. We found smaller fire deficits, 0.3–0.6 M ha, within forest ecosystems adapted to infrequent, high‐severity fire. However, we also acknowledge inherent limitations in evaluating contemporary fire regimes in ecosystems which historically burned infrequently and for which fires were highly episodic. The magnitude of contemporary fire deficits and disconnect in burn severity compared to historic fire regimes have important implications for climate change adaptation. Within forests characterized by low‐ and mixed‐severity historic fire regimes, simply increasing wildfire extent while maintaining current trends in burn severity threatens ecosystem resilience and will potentially drive undesirable ecosystem transformations. Restoring natural fire regimes requires management that facilitates much more low‐ and moderate‐severity fire.

IMHO, Restoring the historic role of fire will require prior mechanical fuels reduction in many areas where fuel loads are higher than historically. That means commercial and non-commercial harvesting, and paying for it, and that spells controversy.

6 thoughts on “The Missing (PNW) Fires”

  1. I have to question some of the assumptions of this paper. I don’t know if it’s certain scientific disciplines who think this way but..

    (1) The idea that there is one past “historic fire regime” for millennia conceivably there were glaciers and warm periods, cool periods, and so on. Then there were humans* actively engaged, strangely absent from this narrative. Unless we know for sure that they were not burning forests.

    (2) Then there is an idea that “ecosystems are adapted” . Adaptation is something that we usually consider to be a property of species. Exactly what is an “ecosystem” in this context, and how does it “adapt” since ” an ecosystem” is an idea about real physical things, and not a thing in itself?

    (3) That you need to reenact the past for things to be OK “describe baseline reference conditions for sustaining species diversity, resiliency, and ecosystem processes and functions (Keane et al. 2009).” If we need to replicate some (randomly?) chosen past state for “ecosystems” to “function” regardless of current and future conditions, seems like we might as well give up now. Note: this idea is clearly not a scientific idea (testable) although it is an idea held by (some) scientists.
    From the paper:

    “Patterns of fire activity occurring over centuries to millennia characterize the fire regime for an ecosystem (Sugihara et al. 2006; Table 1). Pre‐European settlement historical fire regimes describe baseline reference conditions for sustaining species diversity, resiliency, and ecosystem processes and functions (Keane et al. 2009). The discrepancy between historic wildfire extent and recent trends has led to concern over whether the extent and severity of modern fires are outside of the range of historic conditions to which forest ecosystems are adapted (Mallek et al. 2013). Particularly in dry forests with historical high‐frequency, low‐severity fire regimes, there is concern that wildfires are now burning more severely, which could increase the rate at which forests permanently transition to non‐forest ecosystems (Savage and Mast 2005, Collins and Roller 2013, Tepley et al. 2017, Serra‐Diaz et al. 2018). Ecosystem and species reorganization may be more likely in periods of rapid climatic change (Crausbay et al. 2017) and can induce a climate system feedback when conversion from a high‐biomass forest to a low‐biomass non‐forest occurs (Bowman et al. 2013, Hurteau et al. 2016). Uncharacteristic wildfire can also have profound impacts on carbon cycling, species habitat, water quality, and other key ecosystem services (Smith et al. 2011, Adams 2013, Hurteau et al. 2016).”

    * people. From an earlier discussion on this blog by Bob Zybach and others .. referring to Leiburg’s observations in lodgepole country somewhere.

    The largest burns directly chargeable to the Indian occupancy are in Ts. 30 and 31 S., Rs. 8 and 9 E.  In addition to being the largest, they are likewise the most ancient.  The burns cover upward of 60,000 acres, all but 1,000 or 1,100 acres being in a solid block.  This tract appears to have been systematically burned by the Indians during the past three centuries [ca. 1600 to 1855].  Remains of three forests are distinctly traceable in the charred fragments of timber which here and there litter the ground.”

    Curious people might wonder “what evidence did Leiburg have to suggest to him that Native Americans were “systematically burning this area”? Here’s a link to the Zybach post (

    Finally, if we look at t= time from glaciation to now, we have changes due to climate changes, plant and animal movement, evolution, diseases and predators, volcanoes, earthquakes, random other factors, Native Americans and European Americans. In dealing with the vegetation, creatures, and watersheds of today, why wouldn’t we just figure out what we want (including species diversity) and go for it?

    The whole idea of picking some “baseline reference conditions” based on some point in the past seems a bit Garden of Eden- esque to me.

    • Well thought out observations, Sharon. I reckon one way to look at it is: Where are we now, and what changes are warranted? Regardless of past conditions and how present conditions came to be, many areas have much more biomass, live and dead, than is optimal for present times. Looking at the past, however clouded the lens, offers at least some guidance for managing forests — managing for desired future conditions.

  2. If we look more broadly, though, we can think of it as history. History is useful to know and can explain how things got to be the way they are. That is useful information.
    But the idea that the past is generally “guidance” I am not so sure. E.g., the Dust Bowl.. clearly said “don’t do that on the plains” so that’s an example of history being informative. Or the fact that bison used to graze, so perhaps to keep the same kind of plants, we need to continue to have grazing animals. Of course, that would be a social desire to “keep the same kinds of plants” and we’d maybe ask “why?”. As a society, are those conditions more desirable than milo or wheat plants?

    My point is that history and what lessons might be learned from it are both open to discussion by anyone. Even if large amounts of biomass had existed before, that doesn’t mean that we have to emulate it today. We can use our collective minds to say “that doesn’t work for us as a society right now.”

    But my point is that some folks (not necessarily these authors) go directly from “was” to “should be” without a place to have that discussion.. as we used to say about HRV, it’s information not a target. I’d be happy with:

    High-severity fires cause problems in forests, from problems with soil, water quality, to species including trees growing back, regardless of how many acres of high severity there used to be (not convincing to tell Denver Water they should be happy with sediment because it’s within HRV). While fire on the landscape has benefits, it would be better to have less land exposed to high severity fires for those reasons.

  3. “‘We can use our collective minds to say “that doesn’t work for us as a society right now.’”

    We have done that through the public legislative and regulatory processes for federal lands and this is what we decided (as you know):
    “Ecological integrity. The quality or condition of an ecosystem when its dominant ecological
    characteristics (for example, composition, structure, function, connectivity, and species
    composition and diversity) occur within the natural range of variation and can withstand and recover from most perturbations imposed by natural environmental dynamics or human influence.” (36 CFR §219.19)

    I think the last part is probably more illuminating than NRV (which makes it not necessarily the same as “historic”) and is consistent with Steve’s point. Forest plan revisions should be looking at more and less active management as alternative approaches to achieve this and the costs and consequences of each.

    • We need to manage forests for an Un-natural Range of Variation — call it URV — or “perturbations imposed by natural environmental dynamics or human influence.” But it all comes down to managing for resilience, and via multiple-use management, as required by law.


Leave a Comment