Specific leaf area and vapour pressure deficit control live fuel moisture content

Griebel, Anne; Boer, Matthias M.; Blackman, Chris J.; Choat, Brendan; Ellsworth, David S.; Madden, Paul A.; Medlyn, Belinda E.; Dios, Víctor Resco de; Wujeska‐Klause, Agnieszka; Yebra, Marta; Cardenas, Nicolas Younes; Nolan, Rachael H.

doi:10.1111/1365-2435.14271

Cited by 15 publications

(10 citation statements)

References 102 publications

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“…Second, high VPD could also drive the decline of the moisture content of live fuels and plant mortality, both factors also known to increase wildfire danger (Nolan et al 2016;Pimont et al 2019). Contrasting with the conclusions by (Griebel et al 2023), our results suggest that the decrease in dead fuel moisture content but not in live plant moisture content of living leaves and vegetation mortality is likely to mediate this relationship (Figure 3). The emergence of plant hydraulic approaches to fuel moisture prediction (Balaguer-Romano et al 2022;Ruffault et al 2022a), which can better represent the mechanisms driving both live and dead fuel variations, will help in interpreting and predicting climate change effects on wildfire danger.…”

Section: -Mechanisms Possibly Explaining Why Wildfire Activity Is Exa...contrasting

confidence: 90%

How much does VPD drive tree water stress and forest disturbances?

Martin‐StPaul

Ruffault

Guillemot

et al. 2023

Preprint

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Vapor Pressure Deficit (VPD, atmospheric drought) and soil water potential (Ψsoil, soil drought) have both been reported to affect terrestrial plant water stress, plant functions (growth, stomatal conductance, transpiration) and vulnerability to ecosystem disturbances (mortality or vulnerability to wildfires). Which of atmospheric drought or soil drought has the greatest influence on these responses is yet an unresolved question. Using a state-of-the-art soil-plant-atmosphere hydraulic model, we conducted an in-silico experiment where VPD and Ψsoil were manipulated one at a time to quantify the relative importance of atmospheric vs soil drought on most critical plant functions. The model simulates the combined effects of soil drought and atmospheric drought on plant water potential (ΨPlant), a physiologically meaningful metric of plant water status driving plant turgor, stomatal conductance, hydraulic conductance or water content, and thus mortality and fire risks. Contrary to expectations, we showed that VPD had a weaker effect than Ψsoil on tree water stress and forest disturbances risk (i.e leaf moisture content). While physiological responses associated with low water stress such as stomatal closure or turgor loss could be driven by both VPD or soil drought, consequences of extreme water stress such as hydraulic failure, leaf desiccation and vulnerability to wildfires were almost exclusively driven by low Ψsoil. Our results therefore suggest that most plant functions are affected by VPD through its cumulative effect on Ψsoil via increased plant transpiration, rather than through a direct instantaneous effect on plant water potential. We argue that plant hydraulics provide a strong foundation for predicting tree and terrestrial ecosystem responses to climate changes and propose a list of explanations and testable hypotheses to reconcile plant hydraulic theory and observations of soil and atmospheric drought effects on plant functions.

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Section: -Mechanisms Possibly Explaining Why Wildfire Activity Is Exa...contrasting

confidence: 90%

How much does VPD drive tree water stress and forest disturbances?

Martin‐StPaul

Ruffault

Guillemot

et al. 2023

Preprint

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show abstract

“…This allows fires to occur, but they burn with low severity because of a lack of vegetation (Cawson et al., 2018). Higher‐severity fire can still occur, but this requires additional conditions such as strong winds, a low vapour pressure deficit, or other factors that dry vegetation (Griebel et al., 2023), thereby permitting the upward spread of flames (Zylstra et al., 2016).…”

Section: Ecological Evidence Of Historical Fire Effects On Forest Str...mentioning

confidence: 99%

What did it used to look like? A case study from tall, wet mainland Mountain Ash forests prior to British invasion

Lindenmayer,

Taylor,

Bowd

et al. 2024

Austral Ecology

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There has been extensive commentary about historical First Nations' land management in Australia, including in tall, wet forests, and therefore their condition at the time of the British invasion in 1788. Popular texts have interpreted records kept by early British invaders to argue that extensive areas of tall, wet forest were kept open through frequent burning by the First Peoples. However, these interpretations conflict with historical and ecological evidence, which is rarely acknowledged in public discourse. Here, we present evidence about what Victorian Mountain Ash (Eucalyptus regnans) forests were like at the time of the British invasion. We show that at the time of the British invasion, most areas of mainland Mountain Ash forests were likely to have been naturally dense and wet, with: (1) overstorey trees spaced relatively widely; and (2) an understorey consisting of a cool temperate rainforest mesic layer. Ecological and physiological evidence suggests that Mountain Ash forests evolved under conditions where high‐severity wildfire was comparatively rare, leading to patterns of landscape‐level cover dominated by relatively mature forests. This is broadly consistent with reports from the First Peoples, early historical accounts, paintings, and photographs. These forests were not open or park‐like, as may have been the case in some other Australian vegetation types. However, these forests were not wilderness, but places of significance to the First Peoples. Understanding forest structure at the time of the British invasion is critically important in establishing historical reference conditions for guiding appropriate restoration programmes, especially the reinstatement of traditional ecological knowledge, after long periods of post‐British invasion disturbance and degradation. Notably, the dense, wet understorey that characterizes Mountain Ash forests should be recognized as an inherent and entirely natural part of the ecological dynamics of this ecosystem, with approaches to thin, burn, or remove it highly likely to be counterproductive and have a range of detrimental environmental effects.

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“…To our knowledge, there have been neither studies examining temporal changes in VOCs, structural carbohydrates, or physical traits in eucalypt forests, nor studies on how leaf biochemistry and thus, flammability, are driven by phenology [81]. Recently, researchers [19] demonstrated that there is a strong relationship between SLA and water content in eucalypt trees, and that this relationship is driven, in part, by tree phenology and environmental conditions. Similarly, but in a different environment, it was argued [82] that seasonal changes in leaf-level flammability traits may have a significant effect in landscapescale fires.…”

Section: Short-term Vs Long Term Data Collectionmentioning

confidence: 99%

“…However, a formal quantification of the relative importance of each trait is still lacking. Researchers [81] have demonstrated that water content and physical traits are directly related to one another, while others [19] found that SLA could be used to predict leaf water content in eucalypt forests. These studies highlight the need for more research into the interaction of individual vegetation traits on the flammability components of vegetation to predict fire behaviour at different spatial and temporal scales.…”

Section: Linking Species and Leaf-level Flammability To Fire Behaviourmentioning

confidence: 99%

“…Leaf water content, or the amount of water stored in the leaves, is often measured separately from other traits and, thus, is considered as a separate characteristic of leaves. These leaf-level flammability traits are expected to vary between species, between geographical locations, as well as over time in response to different global change drivers [18,19]. Gaining insights into the dynamics of the primary flammability characteristics in vegetation communities is an important step in understanding which eucalypt species are more likely to burn.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

A Review of Leaf-Level Flammability Traits in Eucalypt Trees

Younes,

Yebra,

Boer

et al. 2024

Fire

Self Cite

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With more frequent and intense fires expected under future climate conditions, it is important to understand the mechanisms that control flammability in Australian forests. We followed a systematic review approach to determine which physical traits make eucalypts leaves more or less flammable. Specifically, we reviewed 20 studies that covered 35 eucalypt species across five countries and found that leaf water content, leaf area (LA), and specific leaf area (SLA) are the main drivers of leaf flammability. These traits are easy and straightforward to measure, while more laborious traits (e.g., volatile organic compounds and structural carbohydrates) are seldom measured and reported. Leaf flammability also varies with species, and, while the biochemistry plays a role in how leaves burn, it plays a minor role in fire behaviour at landscape scales. This review highlights the range of different protocols used to measure flammability and leaf water content, warranting caution when comparing traits and results between studies. As a result, we propose a standardised protocol to measure leaf water content and advocate for long-term measurements of leaf traits and flammability. This study not only contributes to the understanding of how and why eucalypt leaves burn but also encourages research into the relative importance of traits in influencing flammability and provides a guide for selecting traits that can be monitored using satellite images to inform fire management policies and strategies.

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Specific leaf area and vapour pressure deficit control live fuel moisture content

Cited by 15 publications

References 102 publications

How much does VPD drive tree water stress and forest disturbances?

How much does VPD drive tree water stress and forest disturbances?

What did it used to look like? A case study from tall, wet mainland Mountain Ash forests prior to British invasion

A Review of Leaf-Level Flammability Traits in Eucalypt Trees

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