Last summer, many Australians were surprised to see wildfires devastating Queensland’s humid rainforests, where large and severe fires are nearly unheard of. This is just one example of how human activities are changing fire patterns around the world, with huge consequences for wildlife.
In a major new article published in Science, we reveal how changes in fire activity threaten more than 4,400 species worldwide with extinction. This includes 19% of birds, 16% of mammals, 17% of dragonflies and 19% of legumes classified as endangered, endangered or vulnerable.
How is the fire fighting activity changing?
Recent wildfires have burned ecosystems where wildfires have historically been rare or absent, from tropical forests in Queensland, Southeast Asia and South America to the tundra of the Arctic Circle.
Exceptionally large and severe fires have been observed even in areas with a long history of fires. For example, the 12.6 million hectares that were burned in eastern Australia during last summer’s devastating fires were of unprecedented size.
This extreme event occurred at a time when fire seasons are lengthening and more extreme forest and bush fires are expected in Australia, Southern Europe and the western United States.
But fire activity isn’t increasing everywhere. Grasslands in countries like Brazil, Tanzania, and the United States have seen fire activity decline.
Risk of extinction in a world on fire
Fire allows many plants to complete their life cycles, creates habitats for a wide range of animals, and maintains a diversity of ecosystems. Many species are adapted to particular fire patterns, such as banksias, plants that release seeds into the resource-rich ash that covers the ground after the fire.
But changing the frequency of fires and in which seasons can damage populations of species like these and transform the ecosystems they depend on.
We reviewed data from the International Union for Conservation of Nature (IUCN) and found that of the 29,304 freshwater and terrestrial species listed as threatened, modified fire regimes pose a threat to more than 4,403.
Most are classified as threatened by an increase in the frequency or intensity of fires.
For example, the endangered wren in semi-arid Australia is confined to isolated areas of habitat, making it vulnerable to large forest fires that can destroy entire local populations.
Similarly, the Kangaroo Island dunnart was classified as critically endangered before losing 95% of its habitat in the devastating fires of 2019-2020.
However, some species and ecosystems are threatened when there is no fire. Frequent fires are an important part of African savannah ecosystems, and less fire activity can lead to shrub invasion. This can displace wild herbivores such as wildebeest who prefer open areas.
How humans change fire regimes
There are three main ways humans are transforming fire activity: global climate change, land use, and the introduction of pest species.
Global climate change changes firefighting regimes by changing fuels such as dry vegetation, which is inflamed like lightning and creating a more extreme fire climate.
Additionally, climate-induced fires can occur before dominant tree species are old enough to produce seeds, and this is reshaping forests in Australia, Canada and the United States.
Humans also alter fire regimes through agriculture, forestry, urbanization and by intentionally lighting or suppressing fires.
Introduced species can also modify fire activity and ecosystems. For example, in the savannah landscapes of northern Australia, invasive shrimp grass increases flammability and the frequency of fire. And invasive animals, such as red foxes and feral cats, prey on native animals exposed in recently burned areas.
It is important to emphasize that cultural, social and economic changes underpin these factors. In Australia, the displacement of indigenous peoples and their nuanced and deliberate use of fire has been linked to the extinction of mammals and is transforming vegetation.