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Background <p>Forest composition and fuel loadings govern wildfire behavior and effects, influencing the vulnerability of forest carbon (C) to emission; however, key uncertainties remain regarding post-fire forest and fuel dynamics and their consequences for C vulnerability to subsequent burns. The objectives of this study were to investigate (1) how forest structure before and after fire compares to the historic natural range of variability; (2) how immediate fire effects and environmental characteristics influence patterns of change in forest structure and biomass over time after fire; and (3) how fire changes forest C vulnerability to emission in future wildfires. We leveraged a unique dataset comprised of nearly immediate (within days) pre- and post-fire forest and fuels measurements in combination with remeasurements spanning a chronosequence of 1–20&#xa0;years after wildfire in mixed-conifer forests in California, USA.</p> Results <p>Fire caused enduring reductions in overstory tree densities (50 ± 14%) and increased height to live crown (+ 2.5 ± 0.7&#xa0;m) thereby shifting forest structure towards the natural range of variability. However, surface fuels rapidly accumulated in the decade after wildfire and standing dead tree biomass increased 249 ± 24% relative to the pre-fire condition and represented 27 ± 3% of all potential fuels. Coarse woody fuels accumulated to pre-fire loadings within 5–7&#xa0;years after wildfire and accumulation was greatest in forests that burned at high severity. The proportion of aboveground ecosystem C contained within all potential fuels increased from 38 ± 2 to 52 ± 3% over time, indicating an increased vulnerability of forest C to emission with future fire.</p> Conclusions <p>Fire-mediated increases in height to live crown and decreases in tree density should improve forest resilience to future fires; however, the structural changes were concomitant with increases in standing dead trees and other fuels that are vulnerable to future emission in future fires. After an initial wildfire in long-unburned forests, as was typical in our study sites, repeated low-intensity fires may help to protect large live trees by consuming remaining and re-accumulated fuels, thereby maintaining forest C sink potential and minimizing C pulses from future fires.</p>

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Post-wildfire effects, fuel dynamics, and overstory structural changes create risks to forest carbon in future fires

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年6月1日

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  • Joseph D. Birch,
  • Matthew B. Dickinson,
  • Eric E. Knapp,
  • Carol Ewell,
  • Jessica R. Miesel

摘要

Background

Forest composition and fuel loadings govern wildfire behavior and effects, influencing the vulnerability of forest carbon (C) to emission; however, key uncertainties remain regarding post-fire forest and fuel dynamics and their consequences for C vulnerability to subsequent burns. The objectives of this study were to investigate (1) how forest structure before and after fire compares to the historic natural range of variability; (2) how immediate fire effects and environmental characteristics influence patterns of change in forest structure and biomass over time after fire; and (3) how fire changes forest C vulnerability to emission in future wildfires. We leveraged a unique dataset comprised of nearly immediate (within days) pre- and post-fire forest and fuels measurements in combination with remeasurements spanning a chronosequence of 1–20 years after wildfire in mixed-conifer forests in California, USA.

Results

Fire caused enduring reductions in overstory tree densities (50 ± 14%) and increased height to live crown (+ 2.5 ± 0.7 m) thereby shifting forest structure towards the natural range of variability. However, surface fuels rapidly accumulated in the decade after wildfire and standing dead tree biomass increased 249 ± 24% relative to the pre-fire condition and represented 27 ± 3% of all potential fuels. Coarse woody fuels accumulated to pre-fire loadings within 5–7 years after wildfire and accumulation was greatest in forests that burned at high severity. The proportion of aboveground ecosystem C contained within all potential fuels increased from 38 ± 2 to 52 ± 3% over time, indicating an increased vulnerability of forest C to emission with future fire.

Conclusions

Fire-mediated increases in height to live crown and decreases in tree density should improve forest resilience to future fires; however, the structural changes were concomitant with increases in standing dead trees and other fuels that are vulnerable to future emission in future fires. After an initial wildfire in long-unburned forests, as was typical in our study sites, repeated low-intensity fires may help to protect large live trees by consuming remaining and re-accumulated fuels, thereby maintaining forest C sink potential and minimizing C pulses from future fires.