Statum Quentis

Fire, oil-rich leaves and a longer burning season

Last updated 2 February 2026

Eucalypts and fire are so closely linked that it is tempting to think of the trees as fireproof. They are not. They are fire-adapted, which is a different thing: many species survive fire and some depend on it, but the adaptation was tuned to a particular rhythm of burning, and that rhythm is changing.

Built to burn and to come back

The leaves of most species are rich in volatile oils. On a hot day a eucalypt forest gives off a faint blue haze, which is the oil evaporating. The same oils make the leaf litter and the canopy unusually flammable, and the loose, stringy bark of several species carries fire up the trunk and throws burning fragments ahead of the front. From the point of view of the tree, this is not a flaw. Fire clears competing vegetation and opens the canopy, and the eucalypt is ready for it. Buds hidden under the bark sprout within weeks of a burn. Lignotubers at the base store energy for regrowth. Woody seed capsules open in the heat and drop seed onto freshly cleared ground.

A patchy fire every couple of decades, mostly at moderate intensity, is what these mechanisms were selected for. A forest can be blackened in spring and green again by the following summer.

What has changed

Three things. First, the fire season in south-eastern Australia has grown longer, with dangerous conditions arriving earlier in spring and persisting later into autumn. Second, the proportion of fires that burn at very high intensity has increased, driven by drier fuels and hotter, windier days. Third, the interval between fires in some regions has shortened to the point where trees are burned again before they have recovered from the last fire or set seed.

Each of these changes undermines a specific adaptation. Epicormic resprouting fails if the fire is hot enough to kill the cambium under the bark. Seed banks are exhausted if a second fire arrives before the young trees have matured, and obligate seeders such as mountain ash can be lost from an area entirely. The 2019–2020 fires burned an area of forest that had no precedent in the modern record and included stands that had already burned in 2009.

Outside Australia

The same traits travel with the tree. Eucalypt plantations in Portugal, Spain, Chile and California have been implicated in severe fires, and the debate about whether they make landscapes more dangerous is heated in its own right. The honest answer is that a dense, unmanaged stand of oil-rich trees in a Mediterranean summer is a fuel load like any other, and probably a worse one than the vegetation it replaced. Whether that risk is acceptable depends on management that is frequently not done.

Further reading