Prescribed fire shrub consumption in a Sierra Nevada mixed-conifer forest

Jaffe, Melissa R.; Collins, Brandon M.; Levine, Jacob; Northrop, Hudson; Malandra, Francesco; Krofcheck, D. J.; Hurteau, Matthew D.; Stephens, Scott L.; North, Malcolm P.

doi:10.1139/cjfr-2020-0454

Cited by 3 publications

(2 citation statements)

References 33 publications

(38 reference statements)

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“…The ameliorative impact of shrub cover on fire severity in this study may be due to higher live fuel moisture levels and generally low rates of litter fall under shrubs, which might have impeded fire's spread. Prostrate ceanothus, in particular, typically does not burn (Ryan et al 2013), and other common species such as snowbrush and greenleaf manzanita often have a dampening effect on fire behavior under milder fire weather conditions (Jaffe et al 2021;North et al 2019), mainly contributing to higher fire intensity and severity when live fuel moistures are low (Agee et al 2002) and/or winds are strong. Alternatively, it may be that plots with higher shrub cover were more likely to be in the Thin-P-fire treatment, which also had the lowest overall pre-fire surface and canopy fuels.…”

Section: Discussionmentioning

confidence: 99%

“…The same attributes of shrubs that possibly contributed to reduced fire severity under wildfire conditions in this study may make prescribed burning more challenging in the future. Live shrubs and surface fuels associated with shrubs do not burn readily in the higher moisture conditions typical of prescribed burns conducted before and after the main wildfire season (Baeza et al 2002;Jaffe et al 2021;Kupfer et al 2020). Thus, increasing shrub cover with treatment represents a paradox for managers.…”

Section: Discussionmentioning

confidence: 99%

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Forest thinning and prescribed burning treatments reduce wildfire severity and buffer the impacts of severe fire weather

Brodie,

Knapp,

Brooks

et al. 2024

fire ecol

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Background The capacity of forest fuel treatments to moderate the behavior and severity of subsequent wildfires depends on weather and fuel conditions at the time of burning. However, in-depth evaluations of how treatments perform are limited because encounters between wildfires and areas with extensive pre-fire data are rare. Here, we took advantage of a 1200-ha randomized and replicated experiment that burned almost entirely in a subsequent wildfire under a wide range of weather conditions. We compared the impacts of four fuel treatments on fire severity, including two thin-only, a thin-burn, a burn-only, and an untreated control. We evaluated four fire severity metrics—tree mortality, average bole char height, percent crown volume consumed (PCVC), and percent crown volume affected (PCVA)—and leveraged data from pre-fire surface and canopy fuels to better understand the mechanisms driving differences in wildfire severity among treatments and how they changed with fire weather. Results We found strong mitigating effects of treatments on fire behavior and tree mortality, despite 20 years having elapsed since mechanical thinning and 10 years since the second entry of prescribed fire. The thin-burn treatment resulted in the lowest fire severity across all four metrics and the untreated control the highest. All four fire severity metrics were positively associated with pre-fire canopy and surface fuel loads, with the exception that PCVC (a fire severity metric related to crown fire behavior) was not associated with surface fuel load. The fire weather conditions under which fuel treatment was most effective varied among fire severity metrics. Fuel treatment benefit was maximized at intermediate burning index values for tree mortality, intermediate to high burning index values for PCVA, and high burning index for bole char height and PCVC. Conclusions We conclude that reducing canopy bulk density via mechanical thinning treatments can help to limit crown fire behavior for 20 years or more. However, reducing surface fuels is necessary to limit scorching and the total crown impacts associated with tree mortality. Further, while fuel treatment effectiveness may decline under the most severe fire weather conditions for fire severity metrics associated with tree mortality, it is maximized under severe fire weather conditions for fire severity metrics associated with crown fire behavior (bole charring and torching). Our results provide strong evidence for the use of fuel treatments to mitigate fire behavior and resulting fire severity even under extreme fire weather conditions.

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