Bushfire lessons: 60 billion rainforest invertebrates lost during Black Summer

An estimated 60 billion invertebrates were lost from southern rainforests during the 2019-2020 Black Summer bushfires, according to new research in Austral Ecology.

“It’s kind of horrifying to think of the of the impact,” says lead researcher Professor Heloise Gibb, an ecologist at La Trobe University.

“It makes us concerned about how long these forests will take to recover, and also whether amongst those 60 billion lost individuals, we may have also lost some species that we might not even know exist yet.”

The researchers looked only at rainforests, which make up a small proportion of the 24 million hectares razed in Australia during what are now known as the Black Summer bushfires.

They also focused on macroinvertebrates (invertebrates that can be seen with the naked eye), meaning the real invertebrate loss from the fires is likely far higher.

“We knew it needed to be done, because invertebrates are often ignored when looking at what happens after fire,” says Gibb.

“There’s a lot of emphasis on the larger animals, and on the plants, and invertebrates get put by the wayside.”

Gibb and colleagues examined 52 temperate rainforest sites across east Gippsland and southern New South Wales, a year after the fires raged through.

Satellite map of southeastern australia with gippsland and southern new south wales highlighted
The study area the researchers scoured. Credit: Professor Heloise Gibb, La Trobe University

“We looked at sites that were unburnt; sites which had a medium burn, which means that the canopy was between 20-80%, burnt; and then severely burnt sites, which had about 80% canopy burn or more,” she says.

The researchers collected leaf litter from set areas on each site, took it back to the lab, and counted all of the insects, arachnids, snails and other invertebrates they found.

“Because we had done a set area, we could calculate up to the landscape level what that would mean for the number of invertebrates left,” says Gibb.

“We calculated the difference between a burnt and unburnt site, in how many invertebrates they’d have, and then we scaled that up to the landscape based on mapping of areas that were at high severity or medium severity burn.”

Two people crouching under log in rainforest looking for invertebrates
An invertebrate survey in the sub-tropical rainforest after the bushfires. Credit: Professor Heloise Gibb

Rainforests generally burn less frequently than drier forests, making them more vulnerable to fire when it comes through.

This means that the current fires raging in Canada, extremely early in the season in a year predicted to be very severe, are likely to suffer a similar proportion of invertebrate loss.

“If those fires in Canada are affecting some of the wetter forests, it’s going to have quite big effects on those species as well,” says Gibb.

Two cockroaches, smaller one crawling over bigger
Trilobite cockroaches in South East Australia. Credit: Professor Heloise Gibb

Efforts to restore these invertebrates, according to Gibb, can include whole-ecosystem restoration to make sure they have leaf litter to live in, moving leaf litter from unburnt areas to burnt areas, and making sure that habitats are connected up so that the invertebrates are able to move between places.

But very little is known about these invertebrates: around 70% remain undescribed.

“That means they don’t have a species name, and we don’t know anything about their ecology,” explains Gibb.

“Once you lose a species, it’s gone. And if it performs a particular function in an ecosystem, then you’re not going to get that back.

“We really need to be spending more time trying to find out more about these invertebrates and their roles in the ecosystem.”

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