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1. Prefire Drought Intensity Drives Postfire Recovery and Mortality in Pinus monticola and Pseudotsuga menziesii Saplings

   https://doi.org/10.1093/forsci/fxae013  

   Sparks, Aaron M; Blanco, Alexander S; Lad, Lauren E; Smith, Alistair M; Adams, Henry D; Tinkham, Wade T (March 2024, Forest Science)

   Abstract Increasing frequency of droughts and wildfire are sparking concerns that these compounded disturbance events are pushing forested ecosystems beyond recovery. An improved understanding of how compounded events affect tree physiology and mortality is needed given the reliance of fire management planning on accurate estimates of postfire tree mortality. In this study, we use a toxicological dose-response approach to quantify the impact of variable-intensity drought and fire on the physiology and mortality of Pinus monticola and Pseudotsuga menziesii saplings. We show that the dose-response relationship between fire intensity and mortality shifts toward increased vulnerability under drought, indicating higher mortality with increasing drought at any fire intensity. The trajectory we observed in postfire chlorophyll fluorescence, an indicator of photosynthetic efficiency and stress, was an effective early warning sign of impending tree death. Postfire mortality modeling shows that accurate mortality classification can be achieved using prefire physiology and morphology metrics combined with fire intensity. Variable importance measures indicate that physiological condition and fire intensity have greater influence on the classification accuracy than morphological metrics. The wide range in drought and fire responses observed between this study and others highlights the need for more research on compound disturbance effects. Study Implications: An improved understanding of how drought and fire affect tree physiology and mortality is needed by natural resource managers looking to predict postfire tree mortality. This study advances our compound disturbance understanding by subjecting conifer saplings to variable drought and fire intensities and quantifying and modeling moderate-term recovery and mortality. The results show reduced physiological recovery and amplified mortality in saplings exposed to greater drought and fire intensity. Overall, this study highlights the importance of physiological condition when modeling tree mortality and could potentially be used to inform current postfire tree mortality models. 

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2. Mortality and Resprouting in California Oak Woodlands Following Mixed-Severity Wildfire

   https://doi.org/10.6084/m9.figshare.13554701  

   Ackerly, David D.; Kozanitas, Melina; Oldfather, Meagan; Papper, Prahlad; Clark, Matthew (January 2019, International oaks)

   null (Ed.)

   We quantified fire severity in the Tubbs Fire (Sonoma Co., CA, October 2017) across different vegetation types, and post-fire mortality and regeneration of tree species in permanent plots at the Pepperwood Preserve. The fire burned 14,895 ha, with > 25% in both medium and high severity. Chaparral and Pinus attenuata stands mostly burned at high severity, while other vegetation types experienced a fairly even distribution of fire severity. The fire killed 50% of saplings (dbh < 1 cm) and 27% of trees (dbh ≥ 1 cm), with higher mortality in high severity patches. Quercus agrifolia, Q. kelloggii, Arbutus menziesii and Umbellularia californica exhibited very high levels of topkill combined with basal resprouting. Pseudotsuga menziesii, which lacks resprouting ability, exhibited high mortality, especially in saplings at high severity. The results provide a baseline to examine potential vegetation change due to high-severity fire, especially in high-severity stands of P. menziesii. 

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3. Assessing the potential fire tolerance of conifer saplings in cold and wet environments using a pyro-ecophysiology approach

   https://doi.org/10.1186/s42408-025-00443-7  

   Blanco, Alexander S; Wilson, David R; Rainsford, Scott W; Harley, Grant L; Bhatta, Roshan P; Halsey, Corbin W; Eldridge, Gabriella M; Garza, Daisy_P Estrada; Brown, L May; Stanley, Madeleine F; et al (December 2026, Fire Ecology)

   Abstract BackgroundClimate change is expected to alter fire return intervals in cold and wet forests in the northwestern United States. This coupled with an expected rise in prescribed fires to restore healthy forests, disproportionately increases risk to saplings of tree species adapted to colder and wetter environments that have low fire resistance. To assess this potential impact, we evaluated the impacts of increasing fire intensity onPicea engelmanniiandThuja plicatasapling physiology, morphology, and mortality. This was achieved using established pyro-ecophysiology experiments where saplings were subjected to controlled surface fires across a range of fire intensities and post-fire growth, physiology and mortality were assessed up to 7 months post-fire. ResultsIn this study we demonstrate that the probability of mortality in the saplings of these two conifer species displays a sigmoidal increase with increasing fire intensity. At fire radiative energy dosage levels < 0.6 MJ m⁻², the observed mortality in both species was lower than predicted by existing crown scorch-based models due to their limited sensitivity at small diameters. Prior to sapling death, chlorophyll fluorescence transiently recovers before a rapid decline, though the timing varies by species and fire intensity dosage. A new general sapling mortality model derived from 7 conifer species is presented. ConclusionsOur results provide predictive tools that managers could use to make informed decisions on the potential impacts of fires on conifer saplings growing in cold and wet environments. Results from both species suggest that chlorophyll fluorescence temporal trends could serve as a potential early warning indicator of fire-induced tree mortality, however, future work should explore whether similar responses are observable using remote sensing data from solar-induced chlorophyll fluorescence and assess potential mechanisms underlying this signal. The general sapling mortality model presented in this paper appears to provide an improved method of predicting conifer sapling mortality over existing approaches, however, research is needed to develop coefficients to adjust the model with tree age and environmental factors. Further studies could also explore whether phenotypic plasticity is driving observed tree responses to fire from plants grown from similar environments. 

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4. Methods to assess fire-induced tree mortality: comparing heated water baths to experimental laboratory fires

   https://doi.org/10.1071/WF24144  

   Partelli-Feltrin, Raquel; Smith, Alistair_M S; Sparks, Aaron M; Foley, Zachary W; Rainsford, Scott W; Harley, Grant L; Moberly, James G; Adams, Henry D; Schwilk, Dylan W; Tinkham, Wade T; et al (December 2025, International Journal of Wildland Fire)

   BackgroundRecent studies looking to advance knowledge of fire-effects on trees have used both heated water baths and experimental laboratory fires to apply heat to plant tissues. AimsWe assessed whether heated water baths and experimental laboratory fires caused xylem cell wall deformation and increased vulnerability to embolism. MethodsUsing Pinus ponderosa and Pinus monticola saplings, we measured impacts using both heated water bath treatments and experimental laboratory fires, with parameters elucidated by prior studies that observed effects associated with lethal outcomes. Key resultsWe show that increased vulnerability to embolism only occurred in one of the species tested when using the heated water baths and did not occur in either species when using the laboratory fire treatments. Neither treatment caused xylem cell deformations. ConclusionsHeated water baths may generate misleading results in some species and therefore should be used with caution when researching effects due to wildland fires. ImplicationsFuture studies should assess the potential of other common fire dynamics proxy methods. 

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5. Low-intensity wildfire in old-growth Douglas-fir and western hemlock forest consumed deep duff, thinned from below, and challenged fire management

   https://doi.org/10.1186/s42408-026-00570-9  

   Dickinson, Matthew B; Birch, Joseph D; Bukoski, Jacob J; Butz, Ramona J; Cox, Elena; Flaherty, Lanny; Hanan, Erin; Miesel, Jessica; Nash, Benjamin E; Seyfried, Georgia S; et al (August 2026, Fire Ecology)

   Abstract BackgroundWhile wind-driven wildfires on the west slopes of the Cascades create extensive areas of stand-replacing (SR) effects, providing opportunities for Douglas-fir regeneration over multi-century time scales, recent studies have shown that forest development is strongly shaped by more frequent fires that cause predominantly non-stand replacing (NSR) effects. These NSR fires generate a complex array of stand structures and forest development pathways both within and outside of SR fire footprints. We build on these studies by describing mechanisms of tree mortality in old-growth Douglas-fir and western hemlock forest burned at low intensity on the 2023 Lookout Fire. Our data were collected in coordination with incident management staff and include pre-fire fuels and vegetation, fire behavior, and immediate post-fire and over-winter effects. We also consider implications for remote sensing and fire management. ResultsAverage rate of spread (< 2 m h⁻¹) and fireline intensity (22 kW m⁻¹) were exceedingly low. High duff loadings (271 Mg ha⁻¹), often derived from downed logs, were 92% consumed while high loadings of coarse-woody debris (131 Mg ha⁻¹) were 36% consumed. Of trees alive before the fire, 20%, including 16% of poles (< 15.2 cm diameter at breast height, DBH), 3% of midstory trees (> 15.2 cm and < 60 cm DBH), and 0.7% of overstory trees (≥ 60 cm DBH), fell during or immediately after the fire, mostly due to combustion impacts on primary roots. Thirty-two percent of snags also fell during this period. Western hemlocks, the most common tree, were more vulnerable to root impacts than other species. Among trees of all species alive before the fire, 40%, mostly pole-sized individuals, either fell or died standing during the first post-fire winter. Trees that died standing had experienced the most crown injury. Of trees that were alive before the fire, 27% were standing alive after winter but about half of those (14% of all pre-fire live trees) experienced significant heating and structural impacts (particularly to roots) that we expect will cause delayed mortality. All told, 74% of trees alive before the fire had fallen or died standing over the winter or are expected to die in the coming years. ConclusionsLow-intensity, NSR fire in old growth consumed deep duff and, between trees that have already died or are expected to die, will cause high mortality (> 70%) below the Douglas-fir dominated overstory. Western hemlocks across the size range were particularly vulnerable to root heating and, we expect, delayed mortality. Treefall during and immediately after fire along with high loadings of duff and downed logs challenged fire suppression operations on the 2023 Lookout Fire but an understanding of why trees fall could help mitigate future treefall hazards for firefighters along planned control lines. 

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