Forest fire threatens global carbon sinks and population centres under rising atmospheric water demand

Clarke, Hamish; Nolan, Rachael H.; Dios, Víctor Resco de; Bradstock, Ross A.; Griebel, Anne; Khanal, S.; Boer, Matthias M.

doi:10.1038/s41467-022-34966-3

Cited by 56 publications

(39 citation statements)

References 71 publications

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“…Moreover, Balch et al (2022) highlighted the importance of night‐time VPD for sustaining active fire when flammability fails to cease at night. In our model, the scaled variable importance of VPD increased by 50% when predicting predawn LFMC compared with the full model (Figure S.9), aligning with a number of recent studies that highlight the commonly underestimated importance of VPD for global wildfire risk (Balch et al, 2022; Chiodi et al, 2021; Clarke et al, 2022; Rao et al, 2022). Since VPD is an important predictor of the moisture content of both dead fuels (Ray et al, 2010; Resco de Dios et al, 2015; Resco de Dios et al, 2021) and live fuels (this study), our finding of the combined importance of VPD and SLA provides a physiological basis for the relationship between burn area and VPD that is increasingly observed globally.…”

Section: Discussionsupporting

confidence: 87%

Section: Introductionmentioning

confidence: 99%

“…A number of recent studies focused on disentangling the importance of VPD for global wildfire risk, e.g. by influencing burn area (Rao et al, 2022), sustaining active fire when flammable conditions are sustained through the night (Balch et al, 2022; Chiodi et al, 2021) or by increasing the frequency of days above critical forest flammability thresholds due to rising temperatures with a changing climate (Clarke et al, 2022). Models that predict instantaneous variation in LFMC based on hydrological variables (such as soil moisture; Vinodkumar et al, 2021) or meteorological drought indices (Pellizzaro et al, 2007; Ruffault et al, 2018; Viegas et al, 2001) fail to account for dynamic plant physiological adjustments and species‐specific plant water‐use strategies or leaf traits, and to our knowledge the combined influence of plant traits, atmospheric and hydrological variables on the instantaneous variability in LFMC have not been assessed anywhere in forest ecosystems in Australia, or elsewhere.…”

Section: Introductionmentioning

confidence: 99%

“…In Australian forests and woodlands, LFMC has been linked to variation in leaf flammability by modifying ignition times (Scarff et al, 2021) and cumulative area burnt by wildfire (Dennison & Moritz, 2009; Nolan et al, 2016; Yebra et al, 2013). Rises in vapour pressure deficit (VPD) cause declines in the moisture content of live fuels and increases in the flammability of dead fuels, both of which have been positively correlated with increases in burn area in forested ecosystems in Australia, North America and Europe (Boer et al, 2017; Clarke et al, 2022; Nolan et al, 2016; Rao et al, 2022; Resco de Dios et al, 2022; Williams et al, 2019). A number of recent studies focused on disentangling the importance of VPD for global wildfire risk, e.g.…”

Section: Introductionmentioning

confidence: 99%

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

et al. 2023

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The live fuel moisture content (LFMC) is an important precondition for wildfire activity, yet it remains challenging to predict LFMC due to the dynamic interplay between atmospheric and hydrological conditions that determine the plant's access to, and loss of water. We monitored LFMC and a range of plant water‐use traits (predawn and midday leaf water potentials [Ψleaf]), leaf traits (specific leaf area [SLA]), hydrological status (soil water content [SWC] in the shallow layer and full profile) and atmospheric variables (air temperature, vapour pressure deficit [VPD], CO2 concentrations) in a mature eucalypt woodland at the Eucalyptus Free‐Air CO2 Enrichment (EucFACE) facility during a drought. We combined plant traits, hydrological status and atmospheric variables into a biophysical model to predict LFMC dynamics, and compared these with predictions of LFMC based on a satellite model and established relationships between Ψleaf and LFMC from pressure–volume curves. Predawn Ψleaf could be well predicted from changes in SWC, but variation in midday Ψleaf and LFMC were more responsive to atmospheric than hydrological variables. The biophysical model explained up to 89% of variability in LFMC and outperformed established approaches to predict LFMC. SLA was the single most important variable to predict LFMC, followed by VPD, which explained 33% of the remaining variability in LFMC. Our study demonstrates that the co‐variation of plant traits and atmospheric and hydrological conditions affect LFMC during drought, suggesting a new way forward for predicting LFMC by combining biophysical and satellite‐based models of LFMC with seasonal forecasts of meteorological and hydrological variables. Read the free Plain Language Summary for this article on the Journal blog.

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Section: Discussionsupporting

confidence: 87%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

et al. 2023

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“…Song et al, 2022). Increased woody thickening, for example in tropical South Asia (Kumar et al, 2021;Scheiter et al, 2020), may also alter fuel loads in regions that are likely to be vulnerable to ignition under a drier and warmer atmosphere (Clarke et al, 2022). This work also highlights the role of VPD in promoting fuel loads and limiting fire ignition and fire spread, a climatic variable that has been linked wildfire occurrence (Diffenbaugh et al, 2021).…”

Section: Discussionmentioning

confidence: 91%

The response of wildfire regimes to Last Glacial Maximum carbon dioxide and climate

Haas

Prentice

Harrison

2023

Preprint

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Abstract. Climate and fuel availability jointly control the incidence of wildfires. The effects of atmospheric CO2 on plant growth influence fuel availability independently of climate; but the relative importance of each in driving large-scale changes in wildfire regimes cannot easily be quantified from observations alone. Here, we use previously developed empirical models to simulate the global spatial pattern of burnt area, fire size and fire intensity for modern and Last Glacial Maximum (LGM; ~ 21,000 ka) conditions using both realistic changes in climate and CO2 and sensitivity experiments to separate their effects. Three different LGM scenarios are used to represent the range of modelled LGM climates. We show large, modelled reductions in burnt area at the LGM compared to the recent period, consistent with the sedimentary charcoal record. This reduction was predominantly driven by the effect of low CO2 on vegetation productivity. The amplitude of the reduction under low CO2 conditions was similar regardless of the LGM climate scenario and was not observed in any LGM scenario when only climate effects were considered, with one LGM climate scenario showing increased burning under these conditions. Fire intensity showed a similar sensitivity to CO2 across different climates but was also sensitive to changes in vapour pressure deficit (VPD). Modelled fire size was reduced under LGM CO2 in many regions but increased under LGM climates because of changes in wind strength, dryness (DD) and diurnal temperature range (DTR). This increase was offset under the coldest LGM climate in the northern latitudes because of a large reduction in VPD. These results emphasis the fact that the relative magnitudes of changes in different climate variables influence the wildfire regime and that different aspects of climate change can have opposing effects. The importance of CO2 effects imply that future projections of wildfire must take rising CO2 into account.

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Climate change may shift metapopulations towards unstable source‐sink dynamics in a fire‐killed, serotinous shrub

Souto‐Veiga,

Groeneveld,

Enright

et al. 2024

Ecology and Evolution

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Climate change, with warming and drying weather conditions, is reducing the growth, seed production, and survival of fire‐adapted plants in fire‐prone regions such as Mediterranean‐type ecosystems. These effects of climate change on local plant demographics have recently been shown to reduce the persistence time of local populations of the fire‐killed shrub Banksia hookeriana dramatically. In principle, extinctions of local populations may be partly compensated by recolonization events through long‐distance dispersal mechanisms of seeds, such as post‐fire wind and bird‐mediated dispersal, facilitating persistence in spatially structured metapopulations. However, to what degree and under which assumptions metapopulation dynamics might compensate for the drastically increased local extinction risk remains to be explored. Given the long timespans involved and the complexity of interwoven local and regional processes, mechanistic, process‐based models are one of the most suitable approaches to systematically explore the potential role of metapopulation dynamics and its underlying ecological assumptions for fire‐prone ecosystems. Here we extend a recent mechanistic, process‐based, spatially implicit population model for the well‐studied fire‐killed and serotinous shrub species B. hookeriana to a spatially explicit metapopulation model. We systematically tested the effects of different ecological processes and assumptions on metapopulation dynamics under past (1988–2002) and current (2003–2017) climatic conditions, including (i) effects of different spatio‐temporal fires, (ii) effects of (likely) reduced intraspecific plant competition under current conditions and (iii) effects of variation in plant performance among and within patches. In general, metapopulation dynamics had the potential to increase the overall regional persistence of B. hookeriana. However, increased population persistence only occurred under specific optimistic assumptions. In both climate scenarios, the highest persistence occurred with larger fires and intermediate to long inter‐fire intervals. The assumption of lower intraspecific plant competition caused by lower densities under current conditions alone was not sufficient to increase persistence significantly. To achieve long‐term persistence (defined as >400 years) it was necessary to additionally consider empirically observed variation in plant performance among and within patches, that is, improved habitat quality in some large habitat patches (≥7) that could function as source patches and a higher survival rate and seed production for a subset of plants, specifically the top 25% of flower producers based on current climate conditions monitoring data. Our model results demonstrate that the impacts of ongoing climate change on plant demographics are so severe that even under optimistic assumptions, the existing metapopulation dynamics shift to an unstable source‐sink dynamic state. Based on our findings, we recommend increased research efforts to understand the consequences of intraspecific trait variation on plant demographics, emphasizing the variation of individual traits both among and within populations. From a conservation perspective, we encourage fire and land managers to revise their prescribed fire plans, which are typically short interval, small fires, as they conflict with the ecologically appropriate spatio‐temporal fire regime for B. hookeriana, and likely as well for many other fire‐killed species.

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Forest fire threatens global carbon sinks and population centres under rising atmospheric water demand

Cited by 56 publications

References 71 publications

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

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

The response of wildfire regimes to Last Glacial Maximum carbon dioxide and climate

Climate change may shift metapopulations towards unstable source‐sink dynamics in a fire‐killed, serotinous shrub

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