Linking Forest Flammability and Plant Vulnerability to Drought

Nolan, Rachael H.; Blackman, Chris J.; Dios, Víctor Resco de; Choat, Brendan; Medlyn, Belinda E.; Li, Ximeng; Bradstock, Ross A.; Boer, Matthias M.

doi:10.3390/f11070779

Cited by 78 publications

(77 citation statements)

References 69 publications

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“…Climatic factors bearing upon the hydraulic regulation of plants, such as the incidence or severity of drought and fire weather, are also expected to shift (Cary et al., 2012; Flannigan et al., 2009; Trenberth et al., 2014). These changing circumstances call for mechanistic rather than empirical models, and have driven a recent effort to bring about a marriage of plant ecophysiology with fire and live fuel modelling (Jolly & Johnson, 2018; Martin‐StPaul, Ruffault, et al., 2018; Nolan et al., 2020). Our data go to the question of how best to develop the representation in fuel models of species differences in live fuel moisture content.…”

Section: Discussionmentioning

confidence: 99%

“…Fuel moisture then reflects a spectrum of plant strategies for managing water balance in the face of shifting soil and atmospheric conditions (Ackerley, 2004; Skelton et al., 2015). Understanding these dynamics requires a link to be drawn between fire science and plant hydraulic ecophysiology (Jolly & Johnson, 2018; Nolan et al., 2020). Developing this link offers the opportunity to predict fuel moisture, and its relationship with wildfire, across species, at large scales and in respect of novel climatic circumstances (Nolan et al., 2020).…”

Section: Introductionmentioning

confidence: 99%

“…Understanding these dynamics requires a link to be drawn between fire science and plant hydraulic ecophysiology (Jolly & Johnson, 2018; Nolan et al., 2020). Developing this link offers the opportunity to predict fuel moisture, and its relationship with wildfire, across species, at large scales and in respect of novel climatic circumstances (Nolan et al., 2020).…”

Section: Introductionmentioning

confidence: 99%

“…This dearth has led to discussion about whether live fuel moisture is simply not an important predictor (of spread rate) in fires at that scale, or whether the power to detect these effects in costly field experiments is constrained by sample size, the range of moisture contents investigated and temporal correlation of live and dead fuel moistures (Alexander & Cruz, 2013; Pimont et al., 2019). Another perspective is that low fuel moisture is a necessary but not sufficient condition for rapid fire spread (Nolan et al., 2020). Meanwhile, recent progress in remote sensing of vegetation moisture has furnished mounting evidence of the importance of live fuel moisture in determining burned area at a landscape or regional scale (Pimont et al., 2019; Yebra et al., 2013).…”

Section: Introductionmentioning

confidence: 99%

“…The degree to which plants dry out under fire weather conditions varies among species (Etlinger & Beall, 2004; Saura‐Mas & Lloret, 2007). Their moisture status depends on a suite of functional traits, ranging from characteristics of leaf cells through stem tissues to whole plant architecture (Nolan et al., 2020). To predict the moisture content of live fuels, it will be necessary to understand how widely these different traits vary, and which exert the strongest influence over plant water status.…”

Section: Introductionmentioning

confidence: 99%

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Effects of plant hydraulic traits on the flammability of live fine canopy fuels

et al. 2021

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Plant species vary in how they regulate moisture and this has implications for their flammability during wildfires. We explored how fuel moisture is shaped by variation within five hydraulic traits: saturated moisture content, cell wall rigidity, cell solute potential, symplastic water fraction and tissue capacitance. Using pressure–volume curves, we measured these hydraulic traits in twigs and distal shoots (i.e. twigs + leaves) in 62 plant species across four wooded communities in south‐eastern Australia. Moisture content of fine fuels was then estimated for circumstances typical of fire weather. These projections were made assuming that under the hot, dry, windy conditions typical of large wildfires, leaves and fine twigs would function at internal water pressures close to wilting point (i.e. turgor loss point, TLP). The effect of different moisture contents at TLP on ignition time was then modelled using a fully mechanistic, finite element model of biomass ignition based on standard principles of physical chemistry. We also measured predawn water potential, an indication of plant access to soil water that is influenced by root architecture. These data were used to model how root traits influence fuel moisture and ignition time. Most variation among species in fuel moisture under fire weather conditions arose from differences in saturated moisture content (3.4‐ to 3.6‐fold variation). Twig capacitance was also an important driver of fuel moisture under these weather conditions (1.9‐ to 2.2‐fold variation in moisture content). A suite of other leaf and root traits influencing how much shoots dry out as they approach wilting point each contributed 1.0‐ to 1.6‐fold variation in projected fuel moisture during fire weather. Fuel moisture variation in turn drove variation in flammability by modifying predicted ignition time. Two main life‐history types in fire‐prone habitats are obligate seeders and resprouters. There were no significant differences between these species groups in estimated fuel moisture during fire weather, nor in any measured hydraulic traits. Live fuel moisture is an important determinant of wildfire activity. Our data show that variation in tissue saturated moisture content among co‐occurring species represents an important ecological store of variation in flammability in the study communities. A free Plain Language Summary can be found within the Supporting Information of this article.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Effects of plant hydraulic traits on the flammability of live fine canopy fuels

et al. 2021

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Ungulates mitigate the effects of drought and shrub encroachment on the fire hazard of Mediterranean oak woodlands

Lecomte,

Bugalho,

Catry

et al. 2024

Ecological Applications

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Climate change is increasing the frequency of droughts and the risk of severe wildfires, which can interact with shrub encroachment and browsing by wild ungulates. Wild ungulate populations are expanding due, among other factors, to favorable habitat changes resulting from land abandonment or land‐use changes. Understanding how ungulate browsing interacts with drought to affect woody plant mortality, plant flammability, and fire hazard is especially relevant in the context of climate change and increasing frequency of wildfires. The aim of this study is to explore the combined effects of cumulative drought, shrub encroachment, and ungulate browsing on the fire hazard of Mediterranean oak woodlands in Portugal. In a long‐term (18 years) ungulate fencing exclusion experiment that simulated land abandonment and management neglect, we investigated the population dynamics of the native shrub Cistus ladanifer, which naturally dominates the understory of woodlands and is browsed by ungulates, comparing areas with (no fencing) and without (fencing) wild ungulate browsing. We also modeled fire behavior in browsed and unbrowsed plots considering drought and nondrought scenarios. Specifically, we estimated C. ladanifer population density, biomass, and fuel load characteristics, which were used to model fire behavior in drought and nondrought scenarios. Overall, drought increased the proportion of dead C. ladanifer shrub individuals, which was higher in the browsed plots. Drought decreased the ratio of live to dead shrub plant material, increased total fuel loading, shrub stand flammability, and the modeled fire parameters, that is, rate of surface fire spread, fireline intensity, and flame length. However, total fuel load and fire hazard were lower in browsed than unbrowsed plots, both in drought and nondrought scenarios. Browsing also decreased the population density of living shrubs, halting shrub encroachment. Our study provides long‐term experimental evidence showing the role of wild ungulates in mitigating drought effects on fire hazard in shrub‐encroached Mediterranean oak woodlands. Our results also emphasize that the long‐term effects of land abandonment can interact with climate change drivers, affecting wildfire hazard. This is particularly relevant given the increasing incidence of land abandonment.

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Patterns of flammability after a sequence of mixed‐severity wildfire in dry eucalypt forests of southern Australia

Barker

Price

Jenkins³

2021

Ecosphere

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Fire severity is the impact of a fire on the landscape, particularly the physical impact on vegetation. Previous studies have established that the severity of a fire can be influenced by the severity of previous fires. Many of these studies were conducted in mixed‐conifer forests, while little is known of this process in temperate eucalypt forests. Barker and Price in their 2018 publication (“Positive severity feedback between consecutive fires in dry eucalypt forests of southern Australia,” Ecosphere 9:e02110) found that high severity fire promotes high severity fire in eucalypt forests, but how is the severity of a fire in these systems affected by the severity of two sequential previous fires? This was investigated using remotely sensed and mapped fire severity data. We found that high severity fire is more likely after at least one previous high severity fire, regardless of its position in the sequence. A sequence of low or moderate severity fire followed by low severity fire resulted in the lowest proportion of high severity in the response fire. Our results suggest that low severity fire maintains the structure of forest fuels, so flammability remains relatively constant. A single high severity fire drives change, altering the structure and flammability of the vegetation and promoting more severe fire. However, the effects were small, so a cycle of high severity fire may be easily broken due to the influence of other variables, such as weather. Repeated high severity fire may also result in a decline in the ability of plants to recover from fire, leading to a compositional and structural change and potentially reducing the flammability of a forest.

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Linking Forest Flammability and Plant Vulnerability to Drought

Cited by 78 publications

References 69 publications

Effects of plant hydraulic traits on the flammability of live fine canopy fuels

Effects of plant hydraulic traits on the flammability of live fine canopy fuels

Ungulates mitigate the effects of drought and shrub encroachment on the fire hazard of Mediterranean oak woodlands

Patterns of flammability after a sequence of mixed‐severity wildfire in dry eucalypt forests of southern Australia

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