Australasian Science Magazine

Tree ferns were producing new fronds within months of the fire. Credit: Forest Phoenix (CSIRO Publishing)

By David Lindenmayer, David Blair, Lachlan McBurney and Sam Banks

How well have animals and plants recovered after Victoria’s Black Saturday bushfires 2 years ago?

The February 2009 wildfires were devastating for Victoria and its people – the worst in the nation’s history in terms of lost life and damage to property. The environmental impacts were also profound, and many spectacular stands of forest were burnt, including ones like the giant mountain ash forests where we have worked for more than 27 years. These forests were portrayed in the media as “destroyed”, but they weren’t. They have begun to recover, often in quite spectacular and unexpected ways.

How the Plants Recover
Mountain ash forests are home to hundreds of species of plants, from giant mountain ash trees – the world’s tallest flowering plant – to liverworts and mosses on logs on the forest floor. These different species are characterised by markedly different recovery strategies:

1. Epicormic resprouting. A large proportion of eucalypt species have the ability to resprout even when most of the outer layers of bark are destroyed by fire. Some species are particularly potent resprouters, like shining gum and red stringybark. However, mountain ash has only very limited capacity for epicormic resprouting and is quite sensitive to wildfire.

2. General resprouting. Tree ferns, some of the most charismatic plants in mountain ash forests, resprout from fronds around the crown, creating verdant new green foliage.

3. Rhizomal resprouting. Rhizomes are interconnected underground root systems that enable rapid resprouting after the above-ground part of a plant is removed by a disturbance, such as fire or mechanical slashing. Common bracken fern is a classic example of a plant species that resprouts from a rhizome.

4. Lignotuberous growth. A lignotuber is a woody swelling at the base of some species of plants that occurs either underground or partly underground. Lignotubers contain reserves that assist a plant to recover if its aerial parts are destroyed. A good example of this strategy is the understorey shrub musk daisy bush, which can resprout after fire, with old-growth plants known to be more than 350 years old.

5. Germination from seed. Many species of plants are killed by disturbances like wildfire, particularly when such disturbances are severe. They recover by germinating from seeds.

How the Animals Recover
Just like plants, there are a range of different mechanisms of animal population recovery. Four are prominent:

1. Survival or persistence. Animals persist in burned areas, and these surviving individuals promote population recovery. Persistence or survival was clearly an important strategy in the case of the mountain brushtail possum. In one of our studies, a population of 19 mountain brushtail possums had, by chance, been fitted with radio-collars for several months prior to the February 2009 fires. In an extraordinary finding, all 19 animals survived the 2009 fire.

2. Rapid new colonisation. Newly burnt forest creates conditions that are highly suitable for some species that previously did not occur in an area. Our surveys of birds in the past 18 months have indicated that one species in particular – the flame robin - has exhibited this kind of response.

3. Disappearance and then rapid colonisation. Some species disappear from a burned stand of forest but then quickly recolonise, sometimes within weeks, months or a handful of years.

4. Disappearance and then slow colonisation. Some attributes of an animal’s habitat can take a long time to develop. Large cavities or hollows in trees are good example. Animals like the greater glider are dependent on large trees with hollows for shelter and nesting. It may take more than 150 years for the kinds of trees with hollows to develop that this species requires. Therefore, if a young stand of forest is burned, it may be 1–2 centuries before the greater glider can return to that stand.

In the 2 years since the 2009 wildfires many people have asked us: will the forest ever recover? Will the animals come back? We have found through our research in Victoria’s mountain ash forests that the answer to both questions is an unequivocal yes. Through an array of different strategies the recovery process has already commenced for both plants and animals.

We plan to track this ongoing recovery process over the coming years and decades in a truly fascinating learning journey of ecological discovery. This new knowledge will significantly improve the understanding of relationships between natural disturbance and forest dynamics, as well as between natural disturbance and biodiversity.