Built to burn

Walk into a Mount Lofty forest three weeks after a fire has come through and you would be forgiven for thinking you were looking at the memory of a forest rather than a living one: every leaf gone, trunks scorched black, the ground a grey felt of ash. Then the bark breaks out in a green fuzz, all the way up the trunk and along the limbs, in a pattern too even to be an accident. It isn’t one. Eucalypts carry a deep strand of dormant buds tucked beneath the insulating thickness of their bark, shielded from heat that would kill an ordinary tree outright, and once the canopy is gone they wake almost in unison (Burrows 2013). This is epicormic resprouting, and it is a different trick from the one going on underground at the same time, where many of the same trees — and a great many shrubs besides — keep a second account: a lignotuber, a woody, bud-and-starch-packed swelling buried in the soil at the base of the trunk, ready to throw up an entirely new stem if everything above ground is lost. Confuse the two and you miss the point: one rescues the tree from within its own bark, the other rebuilds it from the ground up. The mallee eucalypts of the drier country behind the ranges live by the second trick almost exclusively — their multi-stemmed, shrubby habit is nothing but the visible record of having burned and resprouted from the lignotuber, over and over, for as long as anyone has been counting.

Other plants have made a career of waiting for the flames. Banksias and hakeas seal their seed inside a woody cone that only fire’s heat will crack open — serotiny — dropping it onto a bed of bare, ash-fertilised ground at the one moment it is likeliest to take. A wider guild again keeps its seed banked in the soil, inert for years, until it tastes the particular chemistry of smoke, then germinates in a rush across the blackened paddock (Auld 2020). Grasstrees do something subtler still: fire does not force them to flower, but it synchronises them, so a burnt hillside throws up its spikes together the following spring (Lamont & Downes 2011). None of this is fire being kind. It is the Mediterranean bargain — wet winters, killing-dry summers, and fire as the regular closing act — written into the architecture of the plants themselves. Most of this bush is not killed by fire. It is pruned by it, and it has spent its whole evolutionary history getting ready for the next haircut.