I don't know about Australia, but here in Northern California, that's not how it works. 500 years ago, forest fires were common, cool burning, and did more good than harm. Today, it's been so long since the previous fire that there's a huge amount of underbrush and dead material. When a fire comes through, it's so hot that it kills everything, including huge, old growth doug fir trees. However, it's not hot enough to actually incinerate the old growth trees, so you get left with a bunch of standing deads, and plenty of dead wood for another fire.