PARK WATCH March 2019 |
Sera Blair looks at the impacts on and recovery of Victoria’s mountain ash forests.
On 7 February 2009, fire spread rapidly through 78,200 hectares of mountain ash forest in the Central Highlands of Victoria. The history of large fires in these forests (including major fires in 1851, 1926, 1939, 1983 and 2009), coupled with extensive industrial clearfell logging over many decades, has resulted in a dramatic decrease in old growth mountain ash forest in Victoria.
Historically, its estimated that old growth comprised 30-60 per cent of the ecosystem, but now there is only 1.16 per cent left. This history of disturbance has been recognized by the IUCN Red List with their listing of the mountain ash ecosystem as critically endangered.
Old growth areas of mountain ash forests have the greatest abundance of hollow-bearing trees which are a critical habitat resource for many species of possums, gliders and forest birds. They also provide critical areas of refuge during bushfires as they burn at a lower severity than younger forests, or even remain unburnt.
Victoria’s mountain ash forests are one of the most carbon-dense forests in the world. Even after a high severity fire, 86-94 per cent of the carbon remains in their massive trunks and the root systems.
Mountain ash forests are particularly adapted to recover after fire. But in the post-fire condition, the new regeneration is highly vulnerable.
The extensive salvage logging operations that took place in the burnt forests for the three years after Black Saturday did widespread damage to the regenerating forests, with the localized losses of many species. Salvage logging operations move in quickly after fires to recover timber resources before they decay. They clear large areas of forest and destroy natural seedling regeneration with a second fire event post-logging. The loss of hollow-bearing trees was also very significant, with many areas now having no remaining hollow trees. For these areas, and assuming no future fire or logging, it will be well over a century before they once again have trees with hollows present.
Long-term ecological research in the mountain ash forests, led by Professor David Lindenmayer and his team at the Australian National University (ANU), monitored these forests for 25 years before Black Saturday, and has continued in the ten years since.
Since the fires, they have found a strong decline in the populations of Leadbeater’s possum and greater gliders, which they believe is directly linked with the rapid decline in the number of large old hollow-bearing trees. Interestingly, the two most common species of small mammals, agile antechinus and bush rats, recovered after the fire within two generations. Monitoring and genetic research revealed the burnt areas were recolonised by individuals that survived the fires and not through immigration of individuals from unburnt areas.
After the fires, most bird species declined significantly. Only flame robins were found to have a positive response immediately after the fires as they are able to take advantage of the influx of insects into fire effected areas. Ten years on, about half of the bird species in the mountain ash forests are now showing signs of recovery, although birds dependent
on hollows are declining.
The ANU research also found that burnt old forests recover more quickly than young burnt forests. They have more eucalypt seedlings come up after fire, and the ferns and tree ferns recover quickly, benefitting from the increase light due to the loss of tree canopy. Unsurprisingly, areas that were salvage logged after the fires had the lowest plant species diversity.
Victoria’s critically endangered state faunal emblem, Leadbeater’s possum, was severely impacted in the Black Saturday bushfires. They lost 45 per cent of their forest habitat in this single fire event. As a ‘hollow-dependent’ species, that relies on the presence of large old trees with hollows for nesting and protection from predators (owls), they have a complex relationship with fire in their habitat. Mountain ash trees typically take 150 years for tree hollows to begin forming, so Leadbeater’s possum are generally found in forests with old trees. That is not to say it must be old growth; they are actually most commonly found in younger regrowth forest. However, unless the old hollow-bearing trees are present in those younger forests, Leadbeater’s possum will not be present. Typically, it is large old live trees that die in a high severity fire that subsequently stand as a dead hollow bearing trees that are most commonly used by Leadbeater’s possum. The larger the diameter of the tree, the longer it will stand.
Where the Black Saturday bushfires burnt and killed stands of old growth mountain ash forests, like the east side of the protected O’Shannassay water catchment, Leadbeater’s possum habitat will be recovering. While the majority of old growth trees in these areas are now dead, they are starting to crack and decay, creating new opportunities for hollows to form. Stimulated by the fire and the opening up of the forest to light, a new generation of eucalypt and wattle trees have sprung up and are already nearly 20 metres tall. Because this area was not salvage logged, it will be excellent Leadbeater’s possums in the near future.
Now and into the future
The mountain ash forests of the Central Highlands have evolved to cope with periodic fire over many thousands of years. However, due to climate change, the interval between fires is decreasing, and with the added impact of over a century of logging, the forests are now younger and more vulnerable than they have ever been. We need to give them the opportunity to get old again. Their generations are much longer than ours, so we need to be committed to saving these forests for future generations of Victorians, not just future logging rotations.
To have a chance of preserving Victoria’s mountain ash forests, and the myriad of plants and animals that rely on them, we must protect all large old trees from avoidable impacts. We also need to look at protecting the next oldest cohort of the forests, the regrowth trees from the 1939 fires. This cohort is now 80 years old, and rather than viewing it as the ‘best supply of wood products’, we need to start looking at it as the ‘next old growth forest’. At a minimum, all remaining hollow-bearing trees must be fully protected from logging, and ultimately this means a full and just transition for the timber industry from native forest logging into plantations.
Future fires in Victoria’s mountain ash forests are inevitable, and likely to be more frequent and higher intensity due to climate change. While increased control of ignition points can help reduce fire frequency, the impacts of logging and salvage logging are completely avoidable. It is time the Victorian Government values the social, economic and environmental values of our amazing mountain ash forests as water catchments, carbon storage, ecosystems, cultural heritage, tourism opportunities and recreation potential. Creating the Great Forest National Park would support the protection of all of these values to the benefit of all Victorians.
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