Ross Bradstock

Changes in the resilience of resprouting juvenile tree populations in temperate forests due to coupled severe drought and fire

Publisher: Springer Science and Business Media LLC

Date: 25-06-2022

DOI: 10.1007/S11258-022-01249-2

Abstract: Elevated tree mortality and reduced recruitment of new trees linked to drought and fires has been reported across a range of forests over the last few decades. Forests that resprout new foliage epicormically from buds beneath the bark are considered highly resilient to disturbance, but are potentially at risk of elevated mortality, demographic shifts and changes to species composition due to synergistic effects of drought and fire. Despite this, the effects of drought-fire interactions on such forests remain largely unknown. We assessed the effects of drought severity and fire frequency on juvenile mortality, post-fire seedling recruitment and replacement of juvenile trees (balance of recruitment minus mortality) following fire. We compared dry ridgetops and wet gullies (i.e. two forest types that inhabit different topographic positions in the landscape) across a temperate forest in southern Australia. Both forest types experienced higher rates of fire-induced juvenile mortality in areas that had experienced severe drought compared to moderate drought, though mortality rates were generally low across all drought and fire combinations (e.g. 15%). This result indicated that topographic position did little to reduce juvenile mortality when exposed to severe drought plus fire. In wet forest, severe drought also reduced recruitment and replacement of dead juveniles by post-fire seedlings compared to moderate drought. In dry forest net-negative replacement increased with the severity of drought. Across both forest types, the total pool of juveniles was reduced under severe drought (by 16–79 in DSF 5–11 in WSF). Future increases in the frequency of coupled severe drought and fire could potentially increase the susceptibility of resilient temperate forests to major changes in structure and function.

The 2019/2020 mega-fires exposed Australian ecosystems to an unprecedented extent of high-severity fire

Publisher: IOP Publishing

Date: 24-03-2021

DOI: 10.1088/1748-9326/ABEB9E

Abstract: Extreme fire seasons characterised by very large ‘mega-fires’ have demonstrably increased area burnt across forested regions globally. However, the effect of extreme fire seasons on fire severity, a measure of fire impacts on ecosystems, remains unclear. Very large wildfires burnt an unprecedented area of temperate forest, woodland and shrubland across south-eastern Australia in 2019/2020, providing an opportunity to examine the impact of extreme fires on fire severity patterns. We developed an atlas of wildfire severity across south-eastern Australia between 1988 and 2020 to test (a) whether the 2019/2020 fire season was more severe than previous fire seasons, and (b) if the proportion of high-severity fire within the burn extent (HSp) increases with wildfire size and annual area burnt. We demonstrate that the 2019/2020 wildfires in south-eastern Australia were generally greater in extent but not proportionally more severe than previous fires, owing to constant scaling between HSp and annual fire extent across the dominant dry-forest communities. However, HSp did increase with increasing annual fire extent across wet-forests and the less-common rainforest and woodland communities. The absolute area of high-severity fire in 2019/2020 (∼1.8 M ha) was larger than previously seen, accounting for ∼44% of the area burnt by high-severity fire over the past 33 years. Our results demonstrate that extreme fire seasons are a rare but defining feature of fire regimes across forested regions, owing to the disproportionate influence of mega-fires on area burnt.

A broader perspective on the causes and consequences of eastern Australia's 2019–20 season of mega-fires: A response to Adams et al

Publisher: Wiley

Date: 28-05-2020

DOI: 10.1111/GCB.15111

Growth enhancements of elevated atmospheric [CO2] are reduced under drought‐like conditions in temperate eucalypts

Publisher: Wiley

Date: 21-04-2022

DOI: 10.1111/1365-2435.14046

Abstract: Elevated atmospheric [CO 2 ] (‘eCO 2 ’) may alter species composition within vegetation types by favouring the growth of some species over others. However, other related changes in climate conditions, such as increased frequency and severity of drought, may reduce eCO 2 fertilisation effects on plant growth. For many species, it is not known if responses will reflect variability in trait adaptations due to environment. We grew seedlings of nine species of eucalypts indicative of three regional vegetation types (representing a mesic–xeric ecosystem gradient) under two CO 2 concentrations (400 parts per million 640 ppm, i.e. eCO 2 ) and two watering regimes (well‐watered drought‐like conditions). Elevated CO 2 increased biomass accumulation but drought reduced this effect, with mesic species experiencing larger relative reductions. Elevated CO 2 increased the size of storage organs used during resprouting, in the absence of drought. Typical drought responses, such as increased leaf mass per unit area and root mass ratio, were more pronounced in xeric species and were reduced under eCO 2 . Seedling growth and resprouting may be enhanced by eCO 2 , suggesting continued dominance of resprouting species in disturbance‐prone ecosystems, although severe drought is likely to offset eCO 2 fertilisation. Xeric species may cope with drought more effectively under eCO 2 than mesic species due to resource acquisition and storage traits that are more responsive. Read the free Plain Language Summary for this article on the Journal blog.

Warmer and drier conditions have increased the potential for large and severe fire seasons across south‐eastern Australia

Publisher: Wiley

Date: 26-04-2022

DOI: 10.1111/GEB.13514

Abstract: The aims were: (1) to identify the environmental drivers of interannual variation in wildfire extent and severity (2) to examine temporal trends in climatic potential for large and severe wildfires and (3) to assess whether environmental conditions experienced during the 2019–2020 mega‐fire season were anomalous. South‐eastern Australia. 1953–2020. Temperate forests. We used satellite‐derived fire severity mapping from 1988 to 2020 to model the effects of drought, weather and fuels on the annual area burned and the proportion of the area burned that was impacted by high‐severity fire across four bioregions. Trends in wildfire extent and severity were then estimated from 1953 to 2020 using these derived models and gridded climate data to assess changes in climatic potential for large and severe wildfires. Estimates of wildfire extent and severity for the 2019–2020 fire season were then assessed against prior seasons (1953–2019). Annual area burned was positively related to the severity of seasonal drought and frequency of fire weather conditions that promote substantial daily fire growth. Wildfire severity was elevated in years with severe fire weather and increased with increasing antecedent drought in years without severe fire weather. Fuels had a lesser effect on wildfire extent and severity than climate. Potential fire extent and severity have increased over time in response to an increased severity of drought and worsening fire weather conditions. Estimates of wildfire extent and severity during the 2019–2020 fire season approached the upper extreme within each bioregion, owing to widespread extreme climatic conditions. The climatic potential for large and severe forest fires has increased across south‐eastern Australia since the 1950s, probably because of anthropogenic climate change. The magnitude and severity of the 2019–2020 fires reflected climatic conditions that are driving an increase in the size and severity of wildfires.

Cover Image

Publisher: Wiley

Date: 22-10-2021

DOI: 10.1111/PCE.14201

Abstract: The cover image is based on the Invited Review Limits to post‐fire vegetation recovery under climate change by Rachael H. Nolan et al., 0.1111 ce.14176 . image

Limits to post‐fire vegetation recovery under climate change

Publisher: Wiley

Date: 16-09-2021

DOI: 10.1111/PCE.14176

Abstract: Record‐breaking fire seasons in many regions across the globe raise important questions about plant community responses to shifting fire regimes (i.e., changing fire frequency, severity and seasonality). Here, we examine the impacts of climate‐driven shifts in fire regimes on vegetation communities, and likely responses to fire coinciding with severe drought, heatwaves and/or insect outbreaks. We present scenario‐based conceptual models on how overlapping disturbance events and shifting fire regimes interact differently to limit post‐fire resprouting and recruitment capacity. We demonstrate that, although many communities will remain resilient to changing fire regimes in the short‐term, longer‐term changes to vegetation structure, demography and species composition are likely, with a range of subsequent effects on ecosystem function. Resprouting species are likely to be most resilient to changing fire regimes. However, even these species are susceptible if exposed to repeated short‐interval fire in combination with other stressors. Post‐fire recruitment is highly vulnerable to increased fire frequency, particularly as climatic limitations on propagule availability intensify. Prediction of community responses to fire under climate change will be greatly improved by addressing knowledge gaps on how overlapping disturbances and climate change‐induced shifts in fire regime affect post‐fire resprouting, recruitment, growth rates, and species‐level adaptation capacity.

Causes and consequences of eastern Australia's 2019–20 season of mega‐fires

Publisher: Wiley

Date: 22-01-2020

DOI: 10.1111/GCB.14987

Abstract: See Letter to the Editor on this article by Adam et al ., 26, 3756–3758 . See also Response to the Letter by Bradstock et al ., 26, e8–e9 .

Changing Weather Extremes Call for Early Warning of Potential for Catastrophic Fire

Publisher: American Geophysical Union (AGU)

Date: 12-2017

DOI: 10.1002/2017EF000657

Reply to: Logging elevated the probability of high-severity fire in the 2019–20 Australian forest fires

Publisher: Springer Science and Business Media LLC

Date: 14-04-2013

DOI: 10.1038/S41559-022-01716-Z

The severity and extent of the Australia 2019–20 Eucalyptus forest fires are not the legacy of forest management

Publisher: Springer Science and Business Media LLC

Date: 10-05-2021

DOI: 10.1038/S41559-021-01464-6

Abstract: The 2019-20 wildfires in eastern Australia presented a globally important opportunity to evaluate the respective roles of climatic drivers and natural and anthropogenic disturbances in causing high-severity fires. Here, we show the overwhelming dominance of fire weather in causing complete scorch or consumption of forest canopies in natural and plantation forests in three regions across the geographic range of these fires. S ling 32% (2.35 Mha) of the area burnt we found that >44% of the native forests suffered severe canopy damage. Past logging and wildfire disturbance in natural forests had a very low effect on severe canopy damage, reflecting the limited extent logged in the last 25 years (4.5% in eastern Victoria, 5.3% in southern New South Wales (NSW) and 7.8% in northern NSW). The most important variables determining severe canopy damage were broad spatial factors (mostly topographic) followed by fire weather. Timber plantations affected by fire were concentrated in NSW and 26% were burnt by the fires and >70% of the NSW plantations suffered severe canopy damage showing that this intensive means of wood production is extremely vulnerable to wildfire. The massive geographic scale and severity of these Australian fires is best explained by extrinsic factors: an historically anomalous drought coupled with strong, hot dry westerly winds that caused uninterrupted, and often dangerous, fire weather over the entire fire season.

What Do the Australian Black Summer Fires Signify for the Global Fire Crisis?

Publisher: MDPI AG

Date: 17-12-2021

DOI: 10.3390/FIRE4040097

Abstract: The 2019–20 Australian fire season was heralded as emblematic of the catastrophic harm wrought by climate change. Similarly extreme wildfire seasons have occurred across the globe in recent years. Here, we apply a pyrogeographic lens to the recent Australian fires to examine the range of causes, impacts and responses. We find that the extensive area burnt was due to extreme climatic circumstances. However, antecedent hazard reduction burns (prescribed burns with the aim of reducing fuel loads) were effective in reducing fire severity and house loss, but their effectiveness declined under extreme weather conditions. Impacts were disproportionately borne by socially disadvantaged regional communities. Urban populations were also impacted through prolonged smoke exposure. The fires produced large carbon emissions, burnt fire-sensitive ecosystems and exposed large areas to the risk of bio ersity decline by being too frequently burnt in the future. We argue that the rate of change in fire risk delivered by climate change is outstripping the capacity of our ecological and social systems to adapt. A multi-lateral approach is required to mitigate future fire risk, with an emphasis on reducing the vulnerability of people through a reinvigoration of community-level capacity for targeted actions to complement mainstream fire management capacity.

A hydroclimatic model for the distribution of fire on Earth

Publisher: IOP Publishing

Date: 03-2021

DOI: 10.1088/2515-7620/ABEC1F

Abstract: The distribution of fire on Earth has been monitored from space for several decades, yet the geography of global fire regimes has proven difficult to reproduce from interactions of climate, vegetation, terrain, land use and other human activities by empirical and process-based fire models. Here, we propose a simple, yet robust, model for the global distribution of fire potential based on fundamental biophysical constraints controlling fire activity in all biomes. In our ‘top-down’ approach we ignored the dynamics of in idual fires and focus on capturing hydroclimatic constraints on the production and (seasonal) desiccation of fuels to predict the potential mean annual fractional burned area at 0.25° spatial resolution, here estimated by the 0.99 quantile of the observed mean annual fractional burned area ( F 0.99 ) over the 1995-2016 period of the Global Fire Emissions Database (GFED4). We show that 80% of the global variation in F 0.99 can be explained from a combination of mean annual precipitation and potential evapotranspiration. The proposed hydroclimatic model reproduced observed 0.99 quantile fire activity levels equally well across all biomes and provided the first objective underpinning for the dichotomy of global fire regimes in two domains characterised by either fuel production limitations on fire or fuel dryness limitations on fire. A sharp transition between the two climate-fire domains was found to occur at a mean annual aridity index of 1.9 (1.94 ± 0.02). Our model provides a simple but comprehensive basis for predicting fire potential under current and future climates, as well as an overarching framework for estimating effects of human activity via ignition regimes and manipulation of vegetation.

University Of Wollongong

Location: Australia

View Organisation

University Of Sydney

Location: Australia

View Organisation

Linkage Infrastructure, Equipment And Facilities - Grant ID: LE0346454

Start Date: 2002

End Date: 12-2003

Amount: $100,000.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP200101123

Start Date: 06-2020

End Date: 05-2024

Amount: $379,000.00

Funder: Australian Research Council

Linkage Projects - Grant ID: LP0774833

Start Date: 03-2007

End Date: 12-2010

Amount: $450,000.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP220100795

Start Date: 2022

End Date: 10-2025

Amount: $485,000.00

Funder: Australian Research Council

Linkage Projects - Grant ID: LP0776604

Start Date: 07-2007

End Date: 12-2012

Amount: $431,052.00

Funder: Australian Research Council

Linkage Projects - Grant ID: LP0775145

Start Date: 02-2007

End Date: 07-2010

Amount: $306,444.00

Funder: Australian Research Council

Discovery Projects - Grant ID: DP130102576

Start Date: 04-2013

End Date: 03-2017

Amount: $405,000.00

Funder: Australian Research Council

Linkage Projects - Grant ID: LP0668029

Start Date: 06-2006

End Date: 12-2009

Amount: $221,000.00

Funder: Australian Research Council

Linkage Infrastructure, Equipment And Facilities - Grant ID: LE0775666

Start Date: 2007

End Date: 12-2008

Amount: $200,000.00

Funder: Australian Research Council