majored in botany and geology at Melbourne University. When I finished my degree, I wanted to do a postgraduate. They said, "There is a magnificent forest at Wallaby Creek, north of here in the Dubai. It's nearly 300 years old, and it's not regenerating. You can go and find out why." That was where I started in 1949, mapping the forest and finding out why it wasn't regenerating.

In 1982, the fires burned through Wallaby Creek, and I was able to do some research immediately on what the fires did. Before '82, the Wallaby Creek area had been burned many, many times and the miracle was that this patch of forest had never been burned since 1700. That made it quite unique.

The fire in '82 burned in very fast from the usual place, in the Kilmore Gap area. It got to Mount Disappointment, and a cool change took it almost at right angles northeast. Had that cool change been half an hour later, it would have gone far enough in to burn the forest. Eventually it will burn, and that's the story of the whole of the wet eucalypt forests of Australia. Fire is an intrinsic part of the whole environment and the eucalypts have adapted to it in one way or another.

The dry eucalypts have developed all these resistant buds and bark and underground parts. They can be burned and come back within weeks. Mountain ash forests get burned at very, very long intervals of 100 or 200 years. They regenerate because everything else is cleaned off and plenty of nutrients - water, light and seed - come down from the canopy. It is a clean sweep. Every few hundred years you get a new forest.

And it is continually changing. If you don't burn it for 400, 500 or 600 years, it will turn into rainforest. That is the story right up the coast from Cape York to Tasmania - if you don't burn the wet eucalypt forests, they will seed to rainforest. This is because they can't regenerate until they have a massive disturbance of one kind or another, and fire is the main disturbing factor. That suits eucalypts - they are opportunists. They love it and they grow like mad.

They had mills in the bush, and these little tram lines going all over the place. There was no thought to it, but there should have been, because they'd had 1851 and 1886 and 1898 and 1905. They'd had a whole series of fires, but people never learn from history, they just have to repeat it. We have had a catastrophic sequence of fires since white men have been here. The fires have been in the aboriginal time too, but I think in many cases they were smaller and perhaps more frequent in the drier country, and only rarely got away into the wet stuff.

The aboriginal people weren't silly; they knew what they were doing. Making access for hunting animals and all sorts of things. Where we have gone wrong is that in 1851, what we were mad about was gold. The way to find the gold was to burn the country and see the quartz and see where the gold was. This scenario developed along with the whole climatic set up in 1851, and the fire just took off, and there was nothing to stop it.

Often in those days, you had forest leases for cattle, and so the cattlemen were quite happy to burn the bush so they would get good grazing land. But wet forests only need to be burned every 100 to 200 years. They don't want to be burned every 10 or 20 years, which is what we did in the 1800s. This ran counter to the ecology of the whole system.

You see, the trees in these big forests are growing. They're busy putting everything into gaining height, because that is their great asset in dominance over any other plant. Nothing can beat them, and they put on two metres a year.

Now, they don't slow down enough to flower and fruit until they are about 20 years old. Then their height growth is tapering off, and then they start to produce fruits. So this means that if you burn it within this period, you've cooked it, you've done it, because the forest can't regenerate. And that's what happened.

If you go to the mountains of Melbourne you used to see vast areas of bracken fern and scrub. That's because we have done that - we've burned it twice or three times too many and just wiped those intervals of regeneration out.

Where you have the really bad fires like '39 and '83 and this last in 2003, you get huge areas burned and mass regeneration over many, many square kilometers. It's really an extension of the idea of a mosaic.

The Europeans and the Northern Americans developed the idea of a forest regenerating itself, turning itself over by producing a gap and having young plants grow into it. Then they die, and you have this continuous turnover, like a kind of mosaic. That is marvellous.

This mosaic can happen on different scales. You have species which are very light-demanding. They need a big space to grow, and so the mosaic has to be bigger. If you have a shade-bearing species, you can have quite a small gap to regenerate in.

Here you have this pattern of regeneration, which is important. Now fire is an important part of this pattern, and that is what we need people to address, I think.

When I started to do my work in the Wallaby Creek, it was only 10 years after the 1939 fires. This meant I was dealing with forests which were only 10 years old. After the '39 fires, you see, so much of the black forest was just young forest.

There are several stages of development in a mountain ash forest. You start off with seedlings from the eucalypts, which fall when the crowns have been burned. Eucalypts store their seed in capsules, and those capsules in crowns. What normally happens in an unburned forest is that the seed falls like rain throughout summer, and there is a big population of seed harvesting by the ants in the soil. They come out and eat the seed, and they do away with a great percentage of the seed fall.

But when the fire goes through, the capsules dry out and when the fire has moved on, all the seed comes down in one hit. That will saturate any feeding animal, and so there will be excess. Not only that, but then the seed buries itself in the ash and gets hidden.

Germination of the seed in the soil is stimulated because of the heat of the fire. Even the smoke can stimulate a lot of regeneration, but the eucalypts don't need that, they germinate anyway.

Mountain ash is the standard term here, but it's called Eucalyptus Regnans, because it's royal, regal. It's sometimes called swamp gum in Tasmania for some silly reason.

Mountain ash doesn't last much longer than 500 years. You get the occasional one that may factor near the 1000-year mark, but it's a rarity.

Here you have a forest with quite a substantial percentage of volatile oils in the leaves. In a fire those oils evaporate, and you can get the crowns more or less exploding, going 'woof' when the heat gets on to them.

When the crowns get alight, they burn on their own, but they've got to have the support from below. You need a surface fire burning the undergrowth to produce the fuel that is going to get up into the top crowns.

The wind has to whip the fire up off the ground and into the crowns. The higher the forest, the more severe that can be when the fire gets into the crown.

Sometimes you'll get big, gusting winds which sweep the fire swept up into the crowns. Then the surface fires are quite a distance behind, providing the heat to sustain the crown fire.

Once you get a fire going, with the heat rising you get a convection wind as well as the regular wind. And when it's going up slopes, the radiant heat will dry up the stuff ahead. So here you've got the two devils: convection and radiant heat.

In a big forest you can get the flames almost as high as the forest again, 30 metres above the forest.

You've seen the photographs of the flames shooting 30 metres right up in the air above the forests. I went down to Anglesea in '83 because it had been absolutely burned, right out of the bare ground, it was. You looked and you thought, well that was the end of that, but you know that it wouldn't be, it would come back.

And it did. I was standing by a little messmate which was only about four metres high in the heat, and I looked up and I could hear it rustling and I looked down and the seed was falling out of the capsules in this little tree. And I thought, oh, good heavens. So I rushed over and found some capsules which hadn't opened, and collected them, and I took them back.

Now, there was nothing on this ground except for twigs and the fruits attached to it. And I thought to myself, how on earth did the seeds survive? You burned the whole of the crown and most of the leaves and twigs.

I realised that all the heat from a burning tree crown is going up in the air. Where the seeds are is a little bit cooler than further up. It's like a gas burner, you know, the greatest heat is above the fire.

I've heard of this gas build-up and explosion of fire balls. They talked about that in Canberra with the last fire. The witnesses there said volatile gas coming out of the forest just blew up. You can get tornados happening, all sorts of things. At some of the places I saw at Wallaby Creek, you'd come out of mature forest into a young forest, but the ground was strewn with big logs that were criss-crossed in all directions, as though they'd been thrown down by a fire tornado. Things were pretty grim, pretty tremendous. I mean, you don't realise just how catastrophic they can be.

In a great fire, things can be much more devastating than you could even imagine. We don't realise just what can go on. You can get rocks exploding. Surfaces of rocks can explode, and all sorts of things. But I think the thing that staggers me is how resilient the vegetation is. That's what always surprises me.

Plants are smart. If you have a fire which is burning slowly, it will just cook absolutely everything. And that is why so many of these thick-bark eucalypts survive. The fire burns up to them, but it takes quite some time before the heat burns through to the sensitive cambium, and by that time the fire is gone and so they're protected. So the thinness of the bark is crucial - how thick and how thin it is. On the mountain ash, the bark is fairly thin.