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Australian Megafires Could Have Lasting Consequences on Outback Vegetation

Australia’s desperate summer of ferocious bushfires in 2019-2020 burned more than 19 million hectares, devastating plant ecosystems and razing more than 90% of the range of 289 species across the continent. Such comprehensive destruction, coupled with the fact that many species were already weakened by drought, has left experts fearing “regeneration failure and landscape-scale decline” in the country. 

They’re concerned even though many of the species of concern have evolved to be resilient to fire, writes Wildfire Today, citing a study just published in the journal Nature Communications. The research has thrown new light on just how inadequate such natural resilience may be in the face of the intense wildfires spawned by the climate crisis.

“More than eight million hectares of vegetation” burned in the southeast region of Australia alone during the 2019-2020 fire season, the researchers say in the abstract to their study. The disaster was “an event unprecedented in the last 200 years.”

Generating a map of the destruction using “remotely-sensed hotspot data,” the scientists determined that, “across 11 Australian bioregions, 17 major native vegetation groups were severely burnt, and up to 67 to 83% of globally significant rainforests and eucalypt forests and woodlands.”

While most of the affected plant species in those ecosystems possessed protective features like heat-induced seed germination and extra-thick basal bark, fears are that “the massive biogeographic, demographic, and taxonomic breadth of impacts” of the bushfires were too much for these adaptations, leaving the affected ecosystems at risk of large-scale decline.

The species’ vulnerability was already heightened after the years of prolonged drought and extremely high temperatures that occurred prior to the fires. “Impairment of post-fire regeneration has been specifically linked to thresholds in vapour pressure deficit, soil moisture, and maximum surface temperature, as well as fire intensity and seed availability,” explains Wildfire Today.

The study authors note further obstacles to regeneration in the wake of the megafires. “For widespread endemic species with ranges of 500 kilometres or more, the demographic consequences of the 2019-2020 fires are likely unprecedented over at least the past two centuries,” they write. The species are now more susceptible to pests (ranging from attack by myrtle rust fungus to being nibbled by hungry herbivores), as well as to drought.

And still others will be even more susceptible to the next round of fire—especially if the fire season arrives too soon. “Obligate seeding woody species such as the ash eucalypts (eg. Eucalyptus fraxinoides) are likely to be under threat if fires return prior to completion of their typically long sexual maturation periods,” the study notes.

The upshot? There is a clear risk that a catastrophic fire year like 2019-2020 could change the nature of the Australian landscape. “In the most extreme cases tipping points are being reached, resulting in transitions from forest to non-forested vegetation,” writes Wildfire Today.