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Background <p>Bark serves an important function in protecting trees from heat damage in fire-prone ecosystems. As fire increases in Mediterranean-climate systems, so does the need to understand fire adaptations of associated tree species, especially in important but understudied groups such as oaks (<i>Quercus</i> spp.). To determine what bark traits contribute to fire resistance in two widespread California white oak species (<i>Q. douglasii</i> and <i>Q. lobata</i>) and one red oak species (<i>Q. agrifolia</i>), we measured bark thickness, moisture content, and density, and related these variables to Time to Cambium Kill (τ), a metric that quantifies vulnerability to fire-induced trunk tissue death. We conducted heating experiments on the bark of live trees to record τ. We assessed τ as a function of tree trunk diameter and bark thickness, determining “safe” size thresholds for each species. We also compared our field measurements to predictions from two frequently applied τ models. We searched for evidence of species’ fire-adaptedness by comparing bark thickness:size allometry patterns at 50&#xa0;cm and 137&#xa0;cm heights.</p> Results <p>Bark thickness was a much stronger predictor of τ than moisture content or density. <i>Q. agrifolia</i> had a higher bark thickness:stem diameter ratio, lower safe diameter threshold (17.2&#xa0;cm), and higher safe bark thickness threshold (2&#xa0;cm) than <i>Q. douglasii</i> and <i>Q. lobata</i>. Existing models that predict τ as a function of bark properties had modest skill, and our fitted models that accounted for species differences performed better. <i>Q. agrifolia</i> most strongly manifested bark allometry indicative of fire-adaptedness. None of the species showed a fire-adapted pattern of bark tapering with height.</p> Conclusion <p>Bark traits and growth patterns can confer fire adaptation in tree species. <i>Q. agrifolia</i> showed stronger evidence of fire-adapted bark traits than <i>Q. douglasii</i> or <i>Q. lobata</i>. More work is needed to develop reliable general models relating time to trunk tissue kill to bark traits for oaks in fire-prone ecosystems.</p>

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Bark traits and fire vulnerability in three California foothill oak species

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年4月28日

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  • Kaili Brande,
  • Frank W. Davis,
  • Bruce E. Kendall

摘要

Background

Bark serves an important function in protecting trees from heat damage in fire-prone ecosystems. As fire increases in Mediterranean-climate systems, so does the need to understand fire adaptations of associated tree species, especially in important but understudied groups such as oaks (Quercus spp.). To determine what bark traits contribute to fire resistance in two widespread California white oak species (Q. douglasii and Q. lobata) and one red oak species (Q. agrifolia), we measured bark thickness, moisture content, and density, and related these variables to Time to Cambium Kill (τ), a metric that quantifies vulnerability to fire-induced trunk tissue death. We conducted heating experiments on the bark of live trees to record τ. We assessed τ as a function of tree trunk diameter and bark thickness, determining “safe” size thresholds for each species. We also compared our field measurements to predictions from two frequently applied τ models. We searched for evidence of species’ fire-adaptedness by comparing bark thickness:size allometry patterns at 50 cm and 137 cm heights.

Results

Bark thickness was a much stronger predictor of τ than moisture content or density. Q. agrifolia had a higher bark thickness:stem diameter ratio, lower safe diameter threshold (17.2 cm), and higher safe bark thickness threshold (2 cm) than Q. douglasii and Q. lobata. Existing models that predict τ as a function of bark properties had modest skill, and our fitted models that accounted for species differences performed better. Q. agrifolia most strongly manifested bark allometry indicative of fire-adaptedness. None of the species showed a fire-adapted pattern of bark tapering with height.

Conclusion

Bark traits and growth patterns can confer fire adaptation in tree species. Q. agrifolia showed stronger evidence of fire-adapted bark traits than Q. douglasii or Q. lobata. More work is needed to develop reliable general models relating time to trunk tissue kill to bark traits for oaks in fire-prone ecosystems.