Scientists from South Australia have documented the catastrophic decline in a stand of red bark in the Clare Valley, a tree species that survived in the area 40,000 years ago but is now endangered by climate change.
Two extreme droughts caused by climate change since 2000 have been blamed for the “staggering losses” of an isolated population of the South Australian Eucalyptus macrorhyncha species in Spring Gully Conservation Park.
Multiple surveys led by University of South Australian environmental biologists Associate Professor Gunnar Keppel and Udo Sarno recorded tree and biomass losses of more than 40% during the Millennium Drought of 2000-2009 and the Great Drought of 2017-2019.
More than 400 trees were monitored over the course of 15 years, within two years of their death being first reported in 2007.
Scientists say that nearly 250 metric tons of biomass per hectare has disappeared.
“In areas that have experienced complete dieback, overhanging oaks remain the only trees, suggesting that the red garden ecosystem could be replaced by more open trees,” says Professor Keeble.
The research team, which included scientists from the State Herbarium in South Australia and the University of Adelaide, published their findings in the journal. macroenvironmental science.
Genetic data shows that the red bark trees of the Clare Valley were isolated from their closest relatives in Victoria’s Grampians National Park about 40,000 years ago. This predates the Ice Age when Australia was drier and cooler.
“The Clare Valley provided a safe haven that facilitated the survival of the red bark during this arid period. However, current climate change is different from the last ice age. It is associated with much higher temperatures compared to previous time periods, which were cooler but drier.”
The team used trees identified by the Ministry of Environment and Water to document the progress of eucalyptus death in Clare Valley.
During the Millennium Drought, sites with less water and on flat land were most affected, while sites with the greatest heat stress were the most vulnerable during the Great Drought.
Deepak disease is exacerbated by intensive farming and viticulture in the Clare Valley, which may add further stress and prevent migration to sites that may facilitate species survival.
But researchers say there is hope.
“The mortality rate was much lower on south- and east-facing slopes, which are locations that had less sun exposure, and therefore less heat and stress,” says Sarno. “At these sites, some regeneration has also been evident. We hope that the population will continue in pockets that provide a more temperate microclimate.
“If we can manage the populations in Spring Gully Conservation Park, and protect these microclimates, we may be able to save this unique element of Australian biodiversity.”
Gunnar Keppel et al, Population decline in a Pleistocene refuge: gradual desiccation-related death of the southern Australian eucalyptus, macroenvironmental science (2023). DOI: 10.1016/j.scitotenv.2023.162697
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