A Measure of Fuel
A Measure of Fuel
Video by Malcolm McKinnon
Contact Malcolm McKinnonCopyright
Dianne Simmons has made a long-term study of fuel dynamics in forested areas in fire-prone country on the outskirts of Melbourne.
In the wake of the 2009 Victorian bushfires there are calls for a large increase in controlled burning for fuel reduction. Here, Dianne explains how fuel accumulates and argues that controlled burning offers no simple solution.
-Walking in the bush, if it crackles underfoot it's probably going to burn. That's the crackle test. The basic idea is that fires are dependent on fuel and that it's quite clear that if you reduce the amount of fuel, you reduce the intensity of fire.
After 1983, after the big fires, at the time I was actually teaching in a secondary school and I got a bit of an interest in, for a student project, measuring fuel. So we came out to some of these areas-- this is one of them, back in 1984-- and marked out one meter squares and multiple examples of that, scraped up all the leaves. So what you need to do is sort of go down to basically soil level and collect that up, dry it and weigh it.
So I first did that in 1984. And for areas like this, the fuel loads are around about 15 or 17 tons per hectare. So that's about one and a half or so kilograms per meter squared, which is a big garbage bag.
I guess one of the things that we often hear in the media is that one of the problems we have with fire is it's been so long since it was burnt that fuel's been accumulating all that time, over 20 years. In fact, what usually happens in these areas is that as fast as these leaves drop into the system and to pile up on the ground, through winter what we get is wetter soil, and we get a lot of fungi, and we get those little soil fauna, little gooby things. And basically, when it hits the ground, this sort of leaf and twigs and whatever starts to decompose.
So in fact, after a fire, or after the fuel's been removed, fuel accumulates very rapidly because leaves drop, twigs drop, and so on. Very soon though, after a year or so, as soon as these leaves start to rot down, the rate of the leaves dropping in equals the rate of decomposition. So it's only about, say, five years after you've burned that the fuel load stays just about constant.
And I've come back here to this site in 2007 and remeasured the fuel using the same methodology we used in 1984. So what's that, 20-odd years, 23 years later? And effectively, the fuel loads haven't changed over that time.
I think it is a bit of a cultural thing as much as it is a scientific thing or a fire management thing. Part of that story of whether we should be burning it perhaps translates into we should be actively managing everything. And maybe there are some people who think we don't need to actively manage everything in the same obvious, hands-on sort of way .