Population decline in a Pleistocene refugium: Stepwise, drought-related dieback of a South Australian eucalypt

Keppel, Gunnar; Sarnow, Udo; Biffin, Ed; Peters, Stefan; Fitzgerald, Donna L.; Boutsalis, Evan; Waycott, Michelle; Guerin, Greg R.

doi:10.1016/j.scitotenv.2023.162697

Cited by 4 publications

(14 citation statements)

References 90 publications

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“…Many ecosystems are experiencing warmer climates with more extreme events worldwide with more prolonged and hotter droughts (IPCC, 2021). These climate change type droughts are causing the dieback of canopy and understorey species (Breshears et al., 2005; Carnicer et al., 2011; Keppel et al., 2023), which could severely reduce the capacity of grass trees to moderate ambient conditions. In this regard, increasing dieback of the dominant tree species in our study area, E. baxteri and E. obliqua , is of particular concern (Guerin et al., 2023).…”

Section: Discussionmentioning

confidence: 99%

“…For example, in South Australia, where mean surface temperatures have risen by 0.5–1.5°C since 1950 (Guerin et al., 2018), extreme heat events are forecast to increase in intensity, duration, and frequency (Braganza et al., 2013). Extreme heat events can result in a considerable loss of wildlife and plants, as thermal tolerance limits are being exceeded (Allen et al., 2021; Keppel et al., 2023; McKechnie et al., 2021).…”

Section: Introductionmentioning

confidence: 99%

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Understorey vegetation moderates climate in open forests: The role of the skirt‐forming grass tree Xanthorrhoea semiplana F.Muell

Kok,

Bruns,

Guerin

et al. 2023

Austral Ecology

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Microsites are created by abiotic and biotic features of the landscape and may provide essential habitats for the persistence of biota. Forest canopies and understorey plants may moderate wind and solar radiation to create microclimatic conditions that differ considerably from regional climates. Skirt‐forming plants, where senescent leaves create hut‐like cavities around the stem, create microsites that are sheltered from ambient conditions and extreme weather events, constituting potential refuges for wildlife. We investigate day and night temperatures and humidity for four locations (grass tree cavities, soil, 20 cm above‐ground, 1 m above‐ground) in a South Australian forest with relatively open canopy of stringybark eucalypts (Eucalyptus baxteri, E. obliqua) and an understorey of skirt‐forming grass trees (Xanthorrhoea semiplana) at 5, 10, 20, and 40 m from the forest edge. We also measured the percentage of canopy and understorey covers. Generally, temperature and humidity differed significantly between more sheltered (grass tree cavities, soil) and open‐air microsites, with the former being cooler during the day and warmer and more humid during the night. Furthermore, our results suggest that canopy cover tends to decrease, and understorey cover tends to increase, the temperature of microsites. Distance to the edge was not significantly related to temperature for any microsite, suggesting that the edge effect did not extend beyond 10 m from the edge. Overall, grass trees influenced microclimatic conditions by forming a dense understorey and providing cavities that are relatively insulated. The capacity of grass tree cavities to buffer external conditions increased linearly with ambient temperatures, by 0.46°C per degree increase in maximum and 0.25°C per degree decrease in minimum temperatures, potentially offsetting climate warming and enabling persistence of fauna within their thermal limits. These climate moderation properties will make grass trees increasingly important refuges as extreme weather events become more common under anthropogenic climate change.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Understorey vegetation moderates climate in open forests: The role of the skirt‐forming grass tree Xanthorrhoea semiplana F.Muell

Kok,

Bruns,

Guerin

et al. 2023

Austral Ecology

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“…population in the Spring Gully Conservation Park (SGCP) north of Adelaide, South Australia, is at the most western extent of the species natural range. It has likely been disjunct and isolated from populations further eastward for tens of thousands of years [34]. It is considered a relic of a broader species distribution when the climate was more favourable [17].…”

Section: Introductionmentioning

confidence: 99%

“…It is considered a relic of a broader species distribution when the climate was more favourable [17]. After the Millennium Drought between 2001-2009 [28], an increased amount of dieback was observed within SGCP [31,35], and a successive drought, the Big Dry 2017-2019, resulted in further dieback [24,35], especially within the western area of SGCP [34]. Ground investigations of the red stringybark have indicated that monitored trees had a > 40% mortality rate from the beginning of monitoring in 2007 to the last year of monitoring, 2021 [34], with 20 % mortality after the Millennium Drought and 25% mortality after the Big Dry.…”

Section: Introductionmentioning

confidence: 99%

“…After the Millennium Drought between 2001-2009 [28], an increased amount of dieback was observed within SGCP [31,35], and a successive drought, the Big Dry 2017-2019, resulted in further dieback [24,35], especially within the western area of SGCP [34]. Ground investigations of the red stringybark have indicated that monitored trees had a > 40% mortality rate from the beginning of monitoring in 2007 to the last year of monitoring, 2021 [34], with 20 % mortality after the Millennium Drought and 25% mortality after the Big Dry. With an increase in extreme weather events resulting from climate change [34,36,37], droughts are becoming hotter and more prolonged and have been termed climate change-type droughts [15,16].…”

Section: Introductionmentioning

confidence: 99%

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Quantifying Dieback in a Vulnerable Population of Eucalyptus macrorhyncha Using Remote Sensing

Fitzgerald

Peters

Guerin

et al. 2023

Land

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A disjunct population of red stringybark (Eucalyptus macrorhyncha) trees in South Australia is experiencing increasing amounts of dieback. Because the population is considered vulnerable to extinction, we investigated spatiotemporal vegetation changes, quantified the extent of dieback, and determined how topography influences dieback using aerial and satellite imagery. Classification of vegetation health status using hyperspectral aerial imagery indicated that 37% (accuracy = 0.87 Kappa) of the population was unhealthy and potentially experiencing dieback. When correlating this classification with a digital terrain model (DTM), the aspect and amount of solar radiation had the strongest relationship with the presence of unhealthy vegetation. PlanetScope satellite-derived, and spectral index-based analysis indicated that 7% of the red stringybark population experienced negative vegetation health changes during a five-year period (2017–2022), with positive vegetation health changes (9.5%) noted on pole-facing slopes. Therefore, our integrated remote sensing approach documented the extent and spatiotemporal dynamics of dieback, suggesting it could be applied in other studies. Topographical aspects exposed to high-solar radiation were particularly vulnerable to dieback, and pole-facing aspects demonstrated some recovery between droughts. The influence of topography and maps of vegetation health can be used to guide future management and restoration of the population.

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Microrefugia and microclimate: Unraveling decoupling potential and resistance to heatwaves

Finocchiaro,

Médail,

Saatkamp

et al. 2024

Science of The Total Environment

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Population decline in a Pleistocene refugium: Stepwise, drought-related dieback of a South Australian eucalypt

Cited by 4 publications

References 90 publications

Understorey vegetation moderates climate in open forests: The role of the skirt‐forming grass tree Xanthorrhoea semiplana F.Muell

Understorey vegetation moderates climate in open forests: The role of the skirt‐forming grass tree Xanthorrhoea semiplana F.Muell

Quantifying Dieback in a Vulnerable Population of Eucalyptus macrorhyncha Using Remote Sensing

Microrefugia and microclimate: Unraveling decoupling potential and resistance to heatwaves

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