Tree crown injury from wildland fires: causes, measurement and ecological and physiological consequences

Varner, J. Morgan; Hood, Sharon M.; Aubrey, Doug P.; Yedinak, Kara M.; Hiers, J. Kevin; Jolly, W. Matt; Shearman, Timothy M.; McDaniel, Jennifer K.; O’Brien, Joseph J.; Rowell, Eric

doi:10.1111/nph.17539

Cited by 51 publications

(60 citation statements)

References 71 publications

(132 reference statements)

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“…Crown scorch was assessed on each sample tree larger than 2.54 cm dbh as a percent of pre-fire compacted crown length for each of three classes: unburned, scorched and consumed. In this study, we defined crown scorch as the sum of the estimated percent assessed for scorched and consumed crown [10]. For stem char, field crews assessed the percentage of the stem base circumference exhibiting char on the bole at the point where the bole intersects the ground.…”

Section: Methodsmentioning

confidence: 99%

“…We represented drought exposure via the Palmer Drought Severity Index (PDSI), a widely used index that relies on temperature and precipitation data to estimate relative dryness on a standardized scale ranging from very dry (−10) to very wet (10) [25]. We downloaded monthly PDSI data from NOAA's ClimDiv website (doi:10.7289/V5M32STR).…”

Section: Methodsmentioning

confidence: 99%

“…Research has suggested that trees with over 70% crown scorch are at the highest risk of dying within three to five years after a wildfire [8]. High levels of crown scorch diminish survival by reducing photosynthetic capacity, depleting stored, nonstructural carbohydrates needed to regenerate foliage, and are indicative of damage to critical plant tissues other than foliage [10,35]. We expected that drought exposure combined with crown scorch would lead to increasing mortality risk.…”

Section: Logistic Model Performancementioning

confidence: 99%

“…For example, a predictive term was added for bark beetle attacks to increase prediction accuracy in areas of active attacks [8]. Some see a need to augment crown scorch with additional first-order factors, such as indicators of root damage, to account for mortality in trees with little to no crown injury [5,9,10].…”

Section: Introductionmentioning

confidence: 99%

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The Effects of Crown Scorch on Post-fire Delayed Mortality Are Modified by Drought Exposure in California (USA)

Barker

Gray

Fried

2022

Fire

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Accurately predicting the mortality of trees that initially survive a fire event is important for management, such as planning post-fire salvage, planting, and prescribed fires. Although crown scorch has been successfully used to predict post-fire mortality (greater than one-year post-fire), it remains unclear whether other first-order fire effect metrics (e.g., stem char) and information on growing conditions can improve such predictions. Droughts can also elevate mortality and may interact, synergistically, with fire effects to influence post-fire tree survival. We used logistic regression to test whether drought exposure, as indicated by summarized monthly Palmer Drought Severity Index (PDSI) over ten-years could improve predictions of delayed mortality (4–9 years post-fire) at the individual tree level in fire-affected forest inventory and analysis (FIA) plots in California (USA). We included crown scorch, bark thickness, stem char, soil char, slope, and aspect in the model as predictors. We selected the six most prevalent species to include in the model: canyon live oak, Douglas-fir, Jeffrey pine, incense-cedar, ponderosa pine, and white fir. Mean delayed mortality, based on tree count, across all FIA plots across all tree species and plots was 17%, and overall accuracy was good (AUC = 79%). Our model performed well, correctly predicting survivor trees (sensitivity of 0.98) but had difficulty correctly predicting the smaller number of mortality trees (specificity of 0.27) at the standard probability=0.5 mortality threshold. Crown scorch was the most influential predictor of tree mortality. Increasing crown scorch was associated with greater risk of delayed mortality for all six species, with trees exhibiting over 75% crown scorch having a probability of dying that exceeded 0.5. Increasing levels of stem char and soil char (first order indicators) were associated with increasing mortality risk but to less effect than crown scorch. We expected that greater drought exposure would increase delayed post-fire mortality, but we found that increasing drought exposure (median and minimum PDSI) was associated with a modest decrease in post-fire mortality. However, we did find that trees with high levels of crown scorch were less likely to survive with increasing drought exposure (median PDSI). Delayed mortality risk decreased as terrain slope increased. Taken together, our results suggest that trees with substantial crown damage may be more vulnerable to delayed mortality if exposed to drought and that crown scorch is an effective post-fire mortality predictor up to 10 years post-fire.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Logistic Model Performancementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The Effects of Crown Scorch on Post-fire Delayed Mortality Are Modified by Drought Exposure in California (USA)

Barker

Gray

Fried

2022

Fire

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“…Quantitative estimates of fire behavior are best, given that there can be low confidence associated with qualitative estimates. Fire effects, particularly those related to plant physiology (e.g., mortality, embolism, and scorching), directly link to fire intensity (O'Brien et al, 2018;Varner et al, 2021), so fire behavior metrics should ideally focus on heat release, either measured directly or inferred post hoc from biomass consumption. Although authors often report fire temperatures, as estimated by widely used measurement techniques such as thermocouples and temperature-sensitive paints, such approaches are not particularly valuable as temperatures are not mechanistically related to fire behavior or fire effects (Bova and Dickinson, 2008).…”

Section: Ignition Characteristics and Burning Conditionsmentioning

confidence: 99%

Invigorating Prescribed Fire Science Through Improved Reporting Practices

Bonner¹,

Hoffman²,

Kane³

et al. 2021

Front. For. Glob. Change

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Interest in prescribed fire science has grown over the past few decades due to the increasing application of prescribed fire by managers to mitigate wildfire hazards, restore biodiversity, and improve ecosystem resilience. Numerous ecological disciplines use prescribed fire experiments to provide land managers with evidence-based information to support prescribed fire management. Documenting variation in the context and conditions during prescribed fire experimental treatments is critical for management inference, but inconsistencies in reporting critical experimental details can complicate interpretation. Such details are needed to provide ecological and empirical context for data, facilitate experimental replication, enable meta-analyses, and maximize utility for other scientists and practitioners. To evaluate reporting quality in the recent literature, we reviewed 219 prescribed fire experiments from 16 countries published in 11 refereed journals over the last 5 years. Our results suggest substantial shortcomings in the reporting of critical data that compromise the utility of this research. Few studies had specific information on burning conditions such as fuel moisture (22%), quantitative fuel loads (36%), fire weather (53%), and fire behavior (30%). Further, our analysis revealed that 63% of the studies provided precise coordinates for their study area, while 30% of studies indicated the prescribed fire date. Only 54% of the studies provided descriptions of the ignition characteristics. Given these common deficiencies, we suggest minimum reporting standards for future prescribed fire experiments. These standards could be applied to journal author guidelines, directed to researchers and reviewers by the editor, and promoted in the education of fire ecologists. Establishing reporting standards will increase the quality, applicability, and reproducibility of prescribed fire science, facilitate future research syntheses, and foster actionable science.

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Predictive accuracy of post‐fire conifer death declines over time in models based on crown and bole injury

Shearman

Varner

Hood

et al. 2022

Ecological Applications

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A key uncertainty of empirical models of post‐fire tree mortality is understanding the drivers of elevated post‐fire mortality several years following fire, known as delayed mortality. Delayed mortality can represent a substantial fraction of mortality, particularly for large trees that are a conservation focus in western US coniferous forests. Current post‐fire tree mortality models have undergone limited evaluation of how injury level and time since fire interact to influence model accuracy and predictor variable importance. Less severe injuries potentially serve as an indicator for vulnerability to additional stressors such as bark beetle attack or moisture stress. We used a collection of 164,293 individual tree records to examine post‐fire tree mortality in eight western USA conifers: Abies concolor, Abies grandis, Calocedrus decurrens, Larix occidentalis, Pinus contorta, Pinus lambertiana, Pinus ponderosa, and Pseudotsuga menziesii. We evaluated the importance of fire injury predictors on discriminating between surviving trees versus immediate and delayed post‐fire mortality. We fit balanced random forest models for each species using cumulative tree mortality from 1 to 5‐years post‐fire. We compared these results to multi‐class random forest models using first‐year mortality, 2–5‐year mortality, and survival 5‐years post‐fire as a response variable. Crown volume scorched, diameter at breast height, and relative bark char height, were used as predictor variables. The cumulative mortality models all predicted trees that died within 1‐year of fire with high accuracy but failed to predict 2–5‐year mortality. The multi‐class models were an improvement but had lower accuracy for predicting 2–5‐year mortality. Multi‐class model accuracies ranged from 85% to 95% across all species for predicting 1‐year post‐fire mortality, 42%–71% for predicting 2–5‐year mortality, and 64%–85% for predicting trees that lived past 5‐years. Our study highlights the differences in tree species tolerance to fire injury and suggests that including second‐order predictors such as beetle attack or climatic water stress before and after fire will be critical to improve accuracy and better understand the mechanisms and patterns of fire‐caused tree death. Random forest models have potential for management applications such as post‐fire harvesting and simulating future stand dynamics.

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Tree crown injury from wildland fires: causes, measurement and ecological and physiological consequences

Cited by 51 publications

References 71 publications

The Effects of Crown Scorch on Post-fire Delayed Mortality Are Modified by Drought Exposure in California (USA)

The Effects of Crown Scorch on Post-fire Delayed Mortality Are Modified by Drought Exposure in California (USA)

Invigorating Prescribed Fire Science Through Improved Reporting Practices

Predictive accuracy of post‐fire conifer death declines over time in models based on crown and bole injury

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