Ten years on – a decade of intensive biodiversity research after the 2009 Black Saturday wildfires in Victoria’s Mountain Ash forest

Abstract

ABSTRACT The catastrophic 2009 wildfires in the Mountain Ash (Eucalyptus regnans) forests of the Central Highlands of Victoria provided an opportunity to gain new insights into the responses to fire by various elements of the biota. Ongoing long-term monitoring at a large number of permanent field sites for up to 25 years prior to the fire, together with 10 years of post-fire monitoring, has provided an unparalleled series of datasets on mammal, bird, and plant responses on burned and unburned sites. The empirical studies briefly summarized in this paper show patterns of steep declines in large old trees and declines in site occupancy by arboreal marsupials and birds. These changes contrast markedly with the responses of the two most common species of small mammals (the Agile Antechinus [Antechinus agilis] and Bush Rat [Rattus fuscipes]), which recovered within two generations after the fire. Declines in arboreal marsupials, birds and large old trees have also occurred on unburned sites, indicating an ecosystem-wide trend. In general, logging had a greater impact than fire on the majority of groups of birds and plants, particularly post-fire salvage logging that occurred in some areas following the 2009 wildfires. Beyond interactions between fire and post-fire (salvage) logging and their effects on forest biota, we have uncovered evidence of other kinds of interactions in Mountain Ash forests. These include interactions between: (1) the severity of fires and logging history, (2) post-fire bird population recovery and long-term climate and short-term weather conditions, and (3) impacts on forest soils. The structure and landscape composition of the Mountain Ash ecosystem has been radically altered over the last century. This has resulted from the combined impact of several large fires, including the 2009 fires as well as widespread clearfell logging that has been conducted within state forests over the last 50 years. The ecosystem now supports old growth cover that is 1/30th to 1/60th of what it was estimated to have been prior to European settlement. The ongoing decline of key components of the Mountain Ash ecosystem has led to it being classified as Critically Endangered and at high risk of ecosystem collapse. We argue that current forest policy and practices need to better mitigate the effects of fire on this already highly disturbed forest and enhance the possible persistence of species in this ecosystem. Several key strategies are required to do this. First, there is a need to significantly expand the extent of old growth within the Mountain Ash forest estate. This is because fire severity is diminished in such areas. Spatial contagion across old-growth dominated landscapes also may be suppressed relative to landscapes composed primarily of young forest. Allied management strategies include the protection of more mesic parts of Mountain Ash landscapes as these are less likely to burn or at least burn at high severity. Such enhanced protection should include an expanded network of buffers around drainage lines and waterways as these are where fire severity is likely to be lowest and also where old growth elements like large old hollow-bearing trees are more abundant. In addition, all existing living and dead hollow-bearing trees need to be protected by buffers of unlogged forest within wood production forests to promote their standing life and better conserve cavity-dependent fauna such as the Critically Endangered Leadbeater’s Possum (Gymnobelideus leadbeateri) and other declining taxa like the Greater Glider (Petauroides volans).