10 June 2024

The impact of wildfires on understorey and biodiversity rises in Australia

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Gli incendi forestali in Australia impattano anche sul sottobosco nascosto e la biodiversità. Foto: New Matilda from Brisbane Australia, Australia ATTRIBUTION 2.0 GENERIC CC BY 2.0 Deed

In areas affected by wildfires, which are increasingly severe and frequent in Australia as in the rest of the planet, there is a decrease in plant diversity

by Matteo Cavallito

 

The increasing frequency and intensity of fires is having an growing impact on Australia‘s forests by consuming and burning tree crowns. This phenomenon constitutes “a major concern to our country’s ecosystem health, carbon storage and biodiversity.” This is the alarm raised by researchers at the University of Melbourne.

The images of burning trees, they explain, affect our consciousness in a special way. But many problems, at the same time, also occur far from our eyes in those ‘hidden’ forest spaces that have always played a fundamental role for the ecosystem.

The importance of the understorey

Tree crowns, as we know, are attracting particular attention from scientists. The layer of vegetation formed by the tallest plants receives most of the light and stores most of the carbon. But in forests, scientists say, there is actually much more, starting with the understorey – made up of all the trees, shrubs and lower plants growing under the canopy – where the majority of plant diversity is found.

‘The soil beneath that is where the “hidden” understorey resides,’ the researchers write in an article released by the University of Melbourne. Here, they add, “the understorey species’ seeds lie dormant in the soil seedbank, sometimes for decades – waiting for their opportunity to germinate.”

The seed bank in the soil represents the heritage of the plants of the undergrowth as well as a new source of plant growth. “Think of the soil seedbank as an insurance reserve of plant diversity in the event of something calamitous happening to the living understorey plants,” the authors write. “In a world of frequent severe fires, that calamity is becoming a reality”.

Wildfires’ impact

In two separate studies published in February and April this year, Australian researchers analysed the response of understorey forests to fire. Looking at different types of forests – from low-lying shrublands to mountain forests – the scientists found a change in the composition of plant communities. In general, the increased frequency of severe fires has led to a decrease in biodiversity at both lower and higher altitudes.

Morevoer, : “With more fire, there’s a shift towards grassy and herb-dominated understories, particularly at higher elevations – as many shrub species fail to cope with frequent fire.”

With regard to the strategies developed by the plants, it is then noted that some shrubs that survived the fire reached reproductive maturity faster, producing seeds that remained in the soil for a long time and others that germinated in response to the fire. Finally, in different forests, scientists have observed a decrease in the diversity of seeds in the soil.

More frequent fires not only in Australia

The increasing frequency and severity of fires is a widespread phenomenon, not only in Australia. In the USA, according to estimates, the area affected by fires each year has more than tripled in the last four decades. Europe is no exception. According to EU Commission calculations, the fire season in 2019 and 2020 was longer than in the past, while the number of fires and the area burned have exceeded the average of the last twelve years. In this context, changes in plant biodiversity are a problem for the entire ecosystem.

“When ecosystems become dominated by new or different kinds of vegetation, there are consequences for the animals that rely on that habitat, and more broadly, consequences for the flammability of these systems,” the authors continue.

The scientists therefore suggest that affected areas should be restored not only by including tree species that are already present but also important understorey species that are in danger of disappearing.