Are Wildland Fires Increasing Large Patches of Complex Early Seral Forest Habitat?

Figure 1. Ecoregions with pine and mixed conifer forests analyzed for large high-severity fire patches in our study modified from [40]. Two-letter acronyms shown on the map represent different U.S. states.

A new paper, just published by Dominick DellaSala and Chad Hanson, may be of interest to some on this blog. Check it out here. Pasted below are the abstract and the conclusions. -mk

ABSTRACT: High-severity fire creates patches of complex early seral forest (CESF) in mixed-severity fire complexes of the western USA. Some managers and researchers have expressed concerns that large high-severity patches are increasing and could adversely impact old forest extent or lead to type conversions. We used GIS databases for vegetation and fire severity to investigate trends in large (>400 ha) CESF patches in frequent-fire forests of the western USA, analyzing four equal time periods from 1984 to 2015. We detected a significant increase in the total area of large patches relative to the first time period only (1984–1991), but no significant upward trend since the early 1990s. There was no significant trend in the size of large CESF patches between 1984 and 2015. Fire rotation intervals for large CESF patches ranged from ~12 centuries to over 4000 years, depending on the region. Large CESF patches were highly heterogeneous, internally creating ample opportunities for fire-mediated biodiversity. Interior patch areas far removed from the nearest low/moderate-severity edges comprised a minor portion of high-severity patches but may be ecologically important in creating pockets of open forest. There was ample historical evidence of large CESF patches but no evidence of increases that might indicate a current risk of ecosystem-type shifts.

CONSLUSIONS: Our findings have specific management and policy relevance. In particular, we counter claims made by some researchers, and often used by decision-makers, to justify large-scale forest “thinning” and post-fire logging projects—specifically, the assumption that such logging projects are needed to prevent type conversion in response to a perceived increase in CESF patch sizes and conifer regeneration failures in “megafires” (see [6,18,20,22]). Lack of a biodiversity perspective has created underlying tensions among researchers over the role of high-severity fires in maintaining CESF, and we hope that our findings will now inform this ongoing discussion. Additionally, contrary to assumptions made by land managers in the course of proposing extensive post-fire logging and creation of artificial tree plantations following large fires, we found ample evidence of patch heterogeneity–and presumably natural conifer establishment–in large severely burned patches, in addition to the occurrence of large high-severity patches in the historical record. This finding has key relevance to current forest management policy, since the assertion that current large CESF patches are unprecedented is not substantiated by our data but is being used to justify legislative and regulatory proposals to severely weaken environmental laws on U.S. federal lands.

Notably, numerous studies have found high levels of native plant and animal richness and abundance in large fires of mixed severity that produce CESF patches in severely burned areas, see [3,24,25,26,27,28,29,30,31,70,74,75]. Such fires facilitate high levels of beta diversity at landscape scales, providing a broad suite of habitat for both fire-seeking and fire-avoiding species [25], including many early seral birds that have been declining due to a lack of “diverse early seral habitat” [76]. Thus, far from being indicative of “catastrophic” (or “megafire”) ecosystem shifts, large CESF patches have consistently been found to support a unique ecological community that is otherwise most often post-fire logged because of perceptions that this forest type has limited wildlife value, see [25,75]. Instead, we found that large CESF patches are extremely infrequent at landscape scales in ponderosa/Jeffrey-pine and mixed-conifer forests of the western U.S., and whether high-severity fire that produces this important seral stage is increasing in western USA forests remains debatable, e.g., [4,9,10,11,13,14,15,16,19,21,23].

Regarding the human implications of our findings, we recommend that land managers focus limited resources on community fire safety and defensible space of homes as a means of getting to coexistence with wildfire [77,78,79] and for managing wildfire under safe conditions for a myriad of ecosystem benefits.

7 thoughts on “Are Wildland Fires Increasing Large Patches of Complex Early Seral Forest Habitat?”

  1. Trading old growth for brushfields doesn’t bode will for old growth dependent rare species. There is no lack of snags, historically-speaking. We’ve already seen what happens after the fires burn, and re-burn, here in California. The proof is out there and all Hanson can say is that our forests “need larger and more intense wildfires”. Hanson’s ‘cash cow’ seems quite dead, at this point.

    The southern Sierra Nevada has no other options left, on its way to an uncertain future destruction with re-burns and losses of seed sources. The Groveland Ranger District of the Stanislaus NF is the perfect poster child for the loss of old growth through firestorms.

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  2. Matthew, I can’t exactly follow this argument.

    (1) My claim: Some wildfires, particularly large wildfires, burn up trees and have negative impacts on soils and watersheds. They can also have negative impacts on wildlife and fish species. Not to speak of the fact that people like to keep them away from buildings and communities, so feel the need to control where they go.

    (2) Nevertheless, D and H argue that “we counter claims made by some researchers, and often used by decision-makers, to justify large-scale forest “thinning” and post-fire logging projects—specifically, the assumption that such logging projects are needed to prevent type conversion in response to a perceived increase in CESF patch sizes and conifer regeneration failures in “megafires” (see [6,18,20,22]). Lack of a biodiversity perspective has created underlying tensions among researchers over the role of high-severity fires in maintaining CESF, and we hope that our findings will now inform this ongoing discussion.”

    Of course, since we can easily observe conifer regeneration failures IRL or BDA (by driving around), the fact that D and H have not found them in their satellites (or not enough) does not seem compelling.

    (3) This is a straw person argument. Reasons for salvage or planting are usually not generalized. (note they use the term decisions for “large scale” salvage and planting but did not specify what decision maker uses that argument.

    Those are usually much more site- specific and anyone could find the reasons by looking in the NEPA docs under purpose and need. For example, I remember one salvage project in SW Oregon in which the purpose and need was economic recovery of value. A silviculturist and fuels specialist look at the specific situation and make a call based on the specifics of the unit. Montana is not Arizona. The Angeles is not the Mount Baker-Snoqualmie.

    (3) Some of us can look out our windows and see fire areas where trees have not grown back after 15 years. Should we plant? The fact that where we live is “rare” or “precedented or not” based on satellite data across the west isn’t particularly helpful in making that decision.

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    • Wow, that’s really sad and Google maps have even updated (I believe this past May 2019) the on ground view from the highway which provides a wide peripheral view of the destruction.

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  3. I thought it might be worth a quick look at what the Sequoia and Sierra national forests have to say about this in the DEIS for their revised plans (comments due tomorrow). https://www.fs.usda.gov/nfs/11558/www/nepa/3403_FSPLT3_4658769.pdf.
    Some excerpts from the section beginning on p. 244. It looks like some disagreement among scientists. I also want to point out how the natural range of variation (NRV) is referenced here for patch size. It indicates that they have determined what it is and used it in determining desired conditions in the forest plan. Correctly or not I don’t know, but Sharon was looking for examples of whether/how NRV has been applied in practice (and “ecological integrity”).

    “While there is some uncertainty as to exactly how much high-severity fire occurred historically in montane forests, most evidence indicates this to be a smaller proportion of the burned area in these forest types (Safford and Stevens 2017). Moreover, it is also likely that high-severity fire patch sizes have increased considerably in these forests over the past few decades (Miller and Safford 2012, Westerling and Keyser 2016). Historically, these high-severity patches were
    smaller, generally less than 1 to 10 acres and rarely exceeding 200 to 250 acres. Moreover, they
    were not interconnected, resulting from mortality of individual, clumped, or small groups of trees (Safford and Stevens 2017). However, in recent years, mixed conifer and yellow pine forest types have burned severely and extensively, resulting in substantially larger and more interconnected patches of complex early seral forest (Safford and Stevens 2017). This is increasing the total stand-replacing area at high risk of tree regeneration failure in California’s coniferous forests. It has important implications for the long-term resilience and sustainability of forest ecosystems in the region (Stevens et al. 2017).

    “Consequently, many complex early seral forests that were derived from overly dense forest stands with high fuel loads are considered to be outside the natural range of variation and in conflict with other vegetation desired conditions, such as snag densities and surface fuel loads in forest ecosystems. This is especially the case in larger, more interconnected patches of complex early seral forest. Such forests were derived from high-severity patches exceeding the natural range of variation and desired conditions for high-severity patch size. These large patches frequently contain high densities of snags, logs, and shrubs, and lack sufficient tree regeneration to facilitate forest succession and recovery. This would result in low ecological integrity and resilience …”

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    • Thanks, Jon — interesting! Of course, some folks will say that these expanding areas of “complex early seral forests” are desirable.

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  4. I meant to add that the competing science will be a good opportunity for the Forest Service to show off its mastery of the best science requirement of the 2012 Planning Rule §219.3: “The responsible official shall document … what information was determined to be the best available scientific information, explain the basis for that determination, and explain how the information was applied to the issues considered.”

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