In 1967, catastrophic bushfires in Tasmania killed dozens of people – and very nearly destroyed Hobart.

A year later, W.D. Jackson, Professor of Botany at the University of Tasmania, published a short but very influential article on why the fires were so bad. He suggested that after Tasmania’s wet eucalypt forests were burned by severe bushfires, there would be a high-risk period during their regrowth when they are at risk of severely burning again.

This, Jackson theorised, was because regrowing saplings form a very dense canopy, with little distance between living leaves and the leaf litter and understorey plants able to ignite canopy fires. If a second fire sweeps through, he predicted the forests could be replaced with more fire-tolerant scrub.

Was Jackson correct? Is regrowth truly more flammable? It’s very difficult to prove regrowth burns more intensely and accelerates bushfire spread, as it’s not practical to undertake neat, perfectly controlled experiments involving severe bushfires.

But sometimes, scientists get lucky. We took advantage of a natural experiment in 2019, when a severe bushfire burned through a research site spanning old growth wet Tasmanian forests and logged areas of regrowth, giving us access to data before and after the fires.

In our new research, we show Jackson was right. Regrowth does indeed burn more intensely than mature forests.

Why does this matter?

Jackson’s theory has resonated with generations of fire ecologists and fire managers in Australia and internationally, due to how it focuses on the........

© The Conversation