The Metropolitan Fire District in the Port Phillip region has many areas with houses at risk from bushfire because they are adjacent or close to public land, such as the Heathy Woodland reserve. To manage the bushfire risk to nearby houses, in the 1990s and 2000s we did regular fuel reduction burns in the reserve. However, after these burns, some shrub species rapidly grew back, creating a thick mid-storey across the burnt sites.

Staff in the Port Phillip region decided to try another approach to reducing bushfire risk in the Heathy Woodland reserve. In November 2015, we mulched about 11.6 ha of the reserve, leaving some areas unmulched. Two years on, the mulched sites have retained their overstory and there’s been no significant regrowth of the mid-story shrubs, effectively reducing the risk on the site. Since 2015, we have trialled mulching in several other sites in the Metropolitan Fire District.

In early January 2018, a fire in the Heathy Woodland reserve travelled through both mulched and unmulched areas. Afterward, we examined the areas impacted by the fire to see the post-fire differences between the mulched and unmulched areas. We also interviewed the fire crews about the fire behaviour, and how they were able to suppress the fire and bring it under control.

From the examination of the burnt areas, it appears the fire in the mulched areas was less intense and severe than in the unmulched areas. The percentage of canopy burnt was three times less in the mulched areas of the reserve, suggesting that removing mid-storey vegetation in the mulched areas reduced the likelihood of the fire reaching and burning the canopy. This is likely to mean more of the canopy species will survive in coming years.

The interviews with fire crews determined that wind was a key factor in how the fire behaved. We use the Forest Fire Danger Index (FFDI) to measure the degree of danger of the fire, and on the day of the fire in Heathy Woodland reserve, the index suggested severe danger as a result of strong winds. It is difficult to reduce the severity of fires through suppression activities when the FFDI is in the severe range, so the evidence of reduced severity of the fire in the mulched areas was a positive outcome.

So, it is likely the mulching — specifically, removing the mid-storey shrubs — helped reduce the risk of bushfires, as well as the severity and intensity of fires if they occur. Had the wind not influenced the severe FFDI the mulching might have been even more effective at reducing the intensity and severity of the fire.

Page last updated: 15/10/18